@subheading gnutls_alert_get
@anchor{gnutls_alert_get}
@deftypefun {gnutls_alert_description_t} {gnutls_alert_get} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function will return the last alert number received.  This
function should be called when @code{GNUTLS_E_WARNING_ALERT_RECEIVED}  or
@code{GNUTLS_E_FATAL_ALERT_RECEIVED}  errors are returned by a gnutls
function.  The peer may send alerts if he encounters an error.
If no alert has been received the returned value is undefined.

@strong{Returns:} the last alert received, a
@code{gnutls_alert_description_t}  value.
@end deftypefun

@subheading gnutls_alert_get_name
@anchor{gnutls_alert_get_name}
@deftypefun {const char *} {gnutls_alert_get_name} (gnutls_alert_description_t @var{alert})
@var{alert}: is an alert number.

This function will return a string that describes the given alert
number, or @code{NULL} .  See @code{gnutls_alert_get()} .

@strong{Returns:} string corresponding to @code{gnutls_alert_description_t}  value.
@end deftypefun

@subheading gnutls_alert_get_strname
@anchor{gnutls_alert_get_strname}
@deftypefun {const char *} {gnutls_alert_get_strname} (gnutls_alert_description_t @var{alert})
@var{alert}: is an alert number.

This function will return a string of the name of the alert.

@strong{Returns:} string corresponding to @code{gnutls_alert_description_t}  value.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_alert_send
@anchor{gnutls_alert_send}
@deftypefun {int} {gnutls_alert_send} (gnutls_session_t @var{session}, gnutls_alert_level_t @var{level}, gnutls_alert_description_t @var{desc})
@var{session}: is a @code{gnutls_session_t}  type.

@var{level}: is the level of the alert

@var{desc}: is the alert description

This function will send an alert to the peer in order to inform
him of something important (eg. his Certificate could not be verified).
If the alert level is Fatal then the peer is expected to close the
connection, otherwise he may ignore the alert and continue.

The error code of the underlying record send function will be
returned, so you may also receive @code{GNUTLS_E_INTERRUPTED}  or
@code{GNUTLS_E_AGAIN}  as well.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_alert_send_appropriate
@anchor{gnutls_alert_send_appropriate}
@deftypefun {int} {gnutls_alert_send_appropriate} (gnutls_session_t @var{session}, int @var{err})
@var{session}: is a @code{gnutls_session_t}  type.

@var{err}: is an error code returned by another GnuTLS function

Sends an alert to the peer depending on the error code returned by
a gnutls function. This function will call @code{gnutls_error_to_alert()} 
to determine the appropriate alert to send.

This function may also return @code{GNUTLS_E_AGAIN} , or
@code{GNUTLS_E_INTERRUPTED} .

This function historically was always sending an alert to the
peer, even if  @code{err} was inappropriate to respond with an alert
(e.g., @code{GNUTLS_E_SUCCESS} ). Since 3.6.6 this function returns
success without transmitting any data on error codes that
should not result to an alert.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_alert_set_read_function
@anchor{gnutls_alert_set_read_function}
@deftypefun {void} {gnutls_alert_set_read_function} (gnutls_session_t @var{session}, gnutls_alert_read_func @var{func})
@var{session}: is @code{gnutls_session_t}  type

@var{func}: is the function to be called

This function will set a callback to be called when an alert
message is being sent.

@strong{Since:} 3.7.0
@end deftypefun

@subheading gnutls_alpn_get_selected_protocol
@anchor{gnutls_alpn_get_selected_protocol}
@deftypefun {int} {gnutls_alpn_get_selected_protocol} (gnutls_session_t @var{session}, gnutls_datum_t * @var{protocol})
@var{session}: is a @code{gnutls_session_t}  type.

@var{protocol}: will hold the protocol name

This function allows you to get the negotiated protocol name. The
returned protocol should be treated as opaque, constant value and
only valid during the session life.

The selected protocol is the first supported by the list sent
by the client.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

Since 3.2.0
@end deftypefun

@subheading gnutls_alpn_set_protocols
@anchor{gnutls_alpn_set_protocols}
@deftypefun {int} {gnutls_alpn_set_protocols} (gnutls_session_t @var{session}, const gnutls_datum_t * @var{protocols}, unsigned @var{protocols_size}, unsigned int @var{flags})
@var{session}: is a @code{gnutls_session_t}  type.

@var{protocols}: is the protocol names to add.

@var{protocols_size}: the number of protocols to add.

@var{flags}: zero or a sequence of @code{gnutls_alpn_flags_t} 

This function is to be used by both clients and servers, to declare
the supported ALPN protocols, which are used during negotiation with peer.

See @code{gnutls_alpn_flags_t}  description for the documentation of available
flags.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

Since 3.2.0
@end deftypefun

@subheading gnutls_anon_allocate_client_credentials
@anchor{gnutls_anon_allocate_client_credentials}
@deftypefun {int} {gnutls_anon_allocate_client_credentials} (gnutls_anon_client_credentials_t *      @var{sc})
@var{sc}: is a pointer to a @code{gnutls_anon_client_credentials_t}  type.

Allocate a gnutls_anon_client_credentials_t structure.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.
@end deftypefun

@subheading gnutls_anon_allocate_server_credentials
@anchor{gnutls_anon_allocate_server_credentials}
@deftypefun {int} {gnutls_anon_allocate_server_credentials} (gnutls_anon_server_credentials_t *      @var{sc})
@var{sc}: is a pointer to a @code{gnutls_anon_server_credentials_t}  type.

Allocate a gnutls_anon_server_credentials_t structure.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.
@end deftypefun

@subheading gnutls_anon_free_client_credentials
@anchor{gnutls_anon_free_client_credentials}
@deftypefun {void} {gnutls_anon_free_client_credentials} (gnutls_anon_client_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_anon_client_credentials_t}  type.

Free a gnutls_anon_client_credentials_t structure.
@end deftypefun

@subheading gnutls_anon_free_server_credentials
@anchor{gnutls_anon_free_server_credentials}
@deftypefun {void} {gnutls_anon_free_server_credentials} (gnutls_anon_server_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_anon_server_credentials_t}  type.

Free a gnutls_anon_server_credentials_t structure.
@end deftypefun

@subheading gnutls_anon_set_params_function
@anchor{gnutls_anon_set_params_function}
@deftypefun {void} {gnutls_anon_set_params_function} (gnutls_anon_server_credentials_t @var{res}, gnutls_params_function * @var{func})
@var{res}: is a gnutls_anon_server_credentials_t type

@var{func}: is the function to be called

This function will set a callback in order for the server to get
the Diffie-Hellman or RSA parameters for anonymous authentication.
The callback should return @code{GNUTLS_E_SUCCESS}  (0) on success.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.
@end deftypefun

@subheading gnutls_anon_set_server_dh_params
@anchor{gnutls_anon_set_server_dh_params}
@deftypefun {void} {gnutls_anon_set_server_dh_params} (gnutls_anon_server_credentials_t @var{res}, gnutls_dh_params_t @var{dh_params})
@var{res}: is a gnutls_anon_server_credentials_t type

@var{dh_params}: The Diffie-Hellman parameters.

This function will set the Diffie-Hellman parameters for an
anonymous server to use.  These parameters will be used in
Anonymous Diffie-Hellman cipher suites.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.
@end deftypefun

@subheading gnutls_anon_set_server_known_dh_params
@anchor{gnutls_anon_set_server_known_dh_params}
@deftypefun {int} {gnutls_anon_set_server_known_dh_params} (gnutls_anon_server_credentials_t @var{res}, gnutls_sec_param_t @var{sec_param})
@var{res}: is a gnutls_anon_server_credentials_t type

@var{sec_param}: is an option of the @code{gnutls_sec_param_t}  enumeration

This function will set the Diffie-Hellman parameters for an
anonymous server to use.  These parameters will be used in
Anonymous Diffie-Hellman cipher suites and will be selected from
the FFDHE set of RFC7919 according to the security level provided.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a
negative error value.

@strong{Since:} 3.5.6
@end deftypefun

@subheading gnutls_anon_set_server_params_function
@anchor{gnutls_anon_set_server_params_function}
@deftypefun {void} {gnutls_anon_set_server_params_function} (gnutls_anon_server_credentials_t            @var{res}, gnutls_params_function * @var{func})
@var{res}: is a gnutls_certificate_credentials_t type

@var{func}: is the function to be called

This function will set a callback in order for the server to get
the Diffie-Hellman parameters for anonymous authentication.  The
callback should return @code{GNUTLS_E_SUCCESS}  (0) on success.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.
@end deftypefun

@subheading gnutls_anti_replay_deinit
@anchor{gnutls_anti_replay_deinit}
@deftypefun {void} {gnutls_anti_replay_deinit} (gnutls_anti_replay_t @var{anti_replay})
@var{anti_replay}: is a @code{gnutls_anti_replay}  type

This function will deinitialize all resources occupied by the given
anti-replay context.

@strong{Since:} 3.6.5
@end deftypefun

@subheading gnutls_anti_replay_enable
@anchor{gnutls_anti_replay_enable}
@deftypefun {void} {gnutls_anti_replay_enable} (gnutls_session_t @var{session}, gnutls_anti_replay_t @var{anti_replay})
@var{session}: is a @code{gnutls_session_t}  type.

@var{anti_replay}: is a @code{gnutls_anti_replay_t}  type.

Request that the server should use anti-replay mechanism.

@strong{Since:} 3.6.5
@end deftypefun

@subheading gnutls_anti_replay_init
@anchor{gnutls_anti_replay_init}
@deftypefun {int} {gnutls_anti_replay_init} (gnutls_anti_replay_t * @var{anti_replay})
@var{anti_replay}: is a pointer to @code{gnutls_anti_replay_t}  type

This function will allocate and initialize the  @code{anti_replay} context
to be usable for detect replay attacks. The context can then be
attached to a  @code{gnutls_session_t} with
@code{gnutls_anti_replay_enable()} .

@strong{Returns:} Zero or a negative error code on error.

@strong{Since:} 3.6.5
@end deftypefun

@subheading gnutls_anti_replay_set_add_function
@anchor{gnutls_anti_replay_set_add_function}
@deftypefun {void} {gnutls_anti_replay_set_add_function} (gnutls_anti_replay_t @var{anti_replay}, gnutls_db_add_func @var{add_func})
@var{anti_replay}: is a @code{gnutls_anti_replay_t}  type.

@var{add_func}: is the function.

Sets the function that will be used to store an entry if it is not
already present in the resumed sessions database.  This function returns 0
if the entry is successfully stored, and a negative error code
otherwise.  In particular, if the entry is found in the database,
it returns @code{GNUTLS_E_DB_ENTRY_EXISTS} .

The arguments to the  @code{add_func} are:
- @code{ptr} : the pointer set with @code{gnutls_anti_replay_set_ptr()} 
- @code{exp_time} : the expiration time of the entry
- @code{key} : a pointer to the key
- @code{data} : a pointer to data to store

The data set by this function can be examined using
@code{gnutls_db_check_entry_expire_time()}  and @code{gnutls_db_check_entry_time()} .

@strong{Since:} 3.6.5
@end deftypefun

@subheading gnutls_anti_replay_set_ptr
@anchor{gnutls_anti_replay_set_ptr}
@deftypefun {void} {gnutls_anti_replay_set_ptr} (gnutls_anti_replay_t @var{anti_replay}, void * @var{ptr})
@var{anti_replay}: is a @code{gnutls_anti_replay_t}  type.

@var{ptr}: is the pointer

Sets the pointer that will be provided to db add function
as the first argument.
@end deftypefun

@subheading gnutls_anti_replay_set_window
@anchor{gnutls_anti_replay_set_window}
@deftypefun {void} {gnutls_anti_replay_set_window} (gnutls_anti_replay_t @var{anti_replay}, unsigned int @var{window})
@var{anti_replay}: is a @code{gnutls_anti_replay_t}  type.

@var{window}: is the time window recording ClientHello, in milliseconds

Sets the time window used for ClientHello recording.  In order to
protect against replay attacks, the server records ClientHello
messages within this time period from the last update, and
considers it a replay when a ClientHello outside of the period; if
a ClientHello arrives within this period, the server checks the
database and detects duplicates.

For the details of the algorithm, see RFC 8446, section 8.2.

@strong{Since:} 3.6.5
@end deftypefun

@subheading gnutls_auth_client_get_type
@anchor{gnutls_auth_client_get_type}
@deftypefun {gnutls_credentials_type_t} {gnutls_auth_client_get_type} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Returns the type of credentials that were used for client authentication.
The returned information is to be used to distinguish the function used
to access authentication data.

Note that on resumed sessions, this function returns the schema
used in the original session authentication.

@strong{Returns:} The type of credentials for the client authentication
schema, a @code{gnutls_credentials_type_t}  type.
@end deftypefun

@subheading gnutls_auth_get_type
@anchor{gnutls_auth_get_type}
@deftypefun {gnutls_credentials_type_t} {gnutls_auth_get_type} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Returns type of credentials for the current authentication schema.
The returned information is to be used to distinguish the function used
to access authentication data.

Eg. for CERTIFICATE ciphersuites (key exchange algorithms:
@code{GNUTLS_KX_RSA} , @code{GNUTLS_KX_DHE_RSA} ), the same function are to be
used to access the authentication data.

Note that on resumed sessions, this function returns the schema
used in the original session authentication.

@strong{Returns:} The type of credentials for the current authentication
schema, a @code{gnutls_credentials_type_t}  type.
@end deftypefun

@subheading gnutls_auth_server_get_type
@anchor{gnutls_auth_server_get_type}
@deftypefun {gnutls_credentials_type_t} {gnutls_auth_server_get_type} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Returns the type of credentials that were used for server authentication.
The returned information is to be used to distinguish the function used
to access authentication data.

Note that on resumed sessions, this function returns the schema
used in the original session authentication.

@strong{Returns:} The type of credentials for the server authentication
schema, a @code{gnutls_credentials_type_t}  type.
@end deftypefun

@subheading gnutls_base64_decode2
@anchor{gnutls_base64_decode2}
@deftypefun {int} {gnutls_base64_decode2} (const gnutls_datum_t * @var{base64}, gnutls_datum_t * @var{result})
@var{base64}: contains the encoded data

@var{result}: the location of decoded data

This function will decode the given base64 encoded data. The decoded data
will be allocated, and stored into result.

You should use @code{gnutls_free()}  to free the returned data.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.

@strong{Since:} 3.6.0
@end deftypefun

@subheading gnutls_base64_encode2
@anchor{gnutls_base64_encode2}
@deftypefun {int} {gnutls_base64_encode2} (const gnutls_datum_t * @var{data}, gnutls_datum_t * @var{result})
@var{data}: contains the raw data

@var{result}: will hold the newly allocated encoded data

This function will convert the given data to printable data, using
the base64 encoding. This function will allocate the required
memory to hold the encoded data.

You should use @code{gnutls_free()}  to free the returned data.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.

@strong{Since:} 3.6.0
@end deftypefun

@subheading gnutls_buffer_append_data
@anchor{gnutls_buffer_append_data}
@deftypefun {int} {gnutls_buffer_append_data} (gnutls_buffer_t @var{dest}, const void * @var{data}, size_t @var{data_size})
@var{dest}: the buffer to append to

@var{data}: the data

@var{data_size}: the size of  @code{data} 

Appends the provided  @code{data} to the destination buffer.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_bye
@anchor{gnutls_bye}
@deftypefun {int} {gnutls_bye} (gnutls_session_t @var{session}, gnutls_close_request_t @var{how})
@var{session}: is a @code{gnutls_session_t}  type.

@var{how}: is an integer

Terminates the current TLS/SSL connection. The connection should
have been initiated using @code{gnutls_handshake()} .   @code{how} should be one
of @code{GNUTLS_SHUT_RDWR} , @code{GNUTLS_SHUT_WR} .

In case of @code{GNUTLS_SHUT_RDWR}  the TLS session gets
terminated and further receives and sends will be disallowed.  If
the return value is zero you may continue using the underlying
transport layer. @code{GNUTLS_SHUT_RDWR}  sends an alert containing a close
request and waits for the peer to reply with the same message.

In case of @code{GNUTLS_SHUT_WR}  the TLS session gets terminated
and further sends will be disallowed. In order to reuse the
connection you should wait for an EOF from the peer.
@code{GNUTLS_SHUT_WR}  sends an alert containing a close request.

Note that not all implementations will properly terminate a TLS
connection.  Some of them, usually for performance reasons, will
terminate only the underlying transport layer, and thus not
distinguishing between a malicious party prematurely terminating
the connection and normal termination.

This function may also return @code{GNUTLS_E_AGAIN}  or
@code{GNUTLS_E_INTERRUPTED} ; cf.  @code{gnutls_record_get_direction()} .

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code, see
function documentation for entire semantics.
@end deftypefun

@subheading gnutls_certificate_activation_time_peers
@anchor{gnutls_certificate_activation_time_peers}
@deftypefun {time_t} {gnutls_certificate_activation_time_peers} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

This function will return the peer's certificate activation time.

@strong{Returns:} (time_t)-1 on error.

@strong{Deprecated:} @code{gnutls_certificate_verify_peers2()}  now verifies activation times.
@end deftypefun

@subheading gnutls_certificate_allocate_credentials
@anchor{gnutls_certificate_allocate_credentials}
@deftypefun {int} {gnutls_certificate_allocate_credentials} (gnutls_certificate_credentials_t *      @var{res})
@var{res}: is a pointer to a @code{gnutls_certificate_credentials_t}  type.

Allocate a gnutls_certificate_credentials_t structure.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.
@end deftypefun

@subheading gnutls_certificate_client_get_request_status
@anchor{gnutls_certificate_client_get_request_status}
@deftypefun {unsigned} {gnutls_certificate_client_get_request_status} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

Get whether client certificate was requested on the last
handshake or not.

@strong{Returns:} 0 if the peer (server) did not request client
authentication or 1 otherwise.
@end deftypefun

@subheading gnutls_certificate_expiration_time_peers
@anchor{gnutls_certificate_expiration_time_peers}
@deftypefun {time_t} {gnutls_certificate_expiration_time_peers} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

This function will return the peer's certificate expiration time.

@strong{Returns:} (time_t)-1 on error.

@strong{Deprecated:} @code{gnutls_certificate_verify_peers2()}  now verifies expiration times.
@end deftypefun

@subheading gnutls_certificate_free_ca_names
@anchor{gnutls_certificate_free_ca_names}
@deftypefun {void} {gnutls_certificate_free_ca_names} (gnutls_certificate_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_certificate_credentials_t}  type.

This function will delete all the CA name in the given
credentials. Clients may call this to save some memory since in
client side the CA names are not used. Servers might want to use
this function if a large list of trusted CAs is present and
sending the names of it would just consume bandwidth without providing
information to client.

CA names are used by servers to advertise the CAs they support to
clients.
@end deftypefun

@subheading gnutls_certificate_free_cas
@anchor{gnutls_certificate_free_cas}
@deftypefun {void} {gnutls_certificate_free_cas} (gnutls_certificate_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_certificate_credentials_t}  type.

This function was operational on very early versions of gnutls.
Due to internal refactorings and the fact that this was hardly ever
used, it is currently a no-op.
@end deftypefun

@subheading gnutls_certificate_free_credentials
@anchor{gnutls_certificate_free_credentials}
@deftypefun {void} {gnutls_certificate_free_credentials} (gnutls_certificate_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_certificate_credentials_t}  type.

Free a gnutls_certificate_credentials_t structure.

This function does not free any temporary parameters associated
with this structure (ie RSA and DH parameters are not freed by this
function).
@end deftypefun

@subheading gnutls_certificate_free_crls
@anchor{gnutls_certificate_free_crls}
@deftypefun {void} {gnutls_certificate_free_crls} (gnutls_certificate_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_certificate_credentials_t}  type.

This function will delete all the CRLs associated
with the given credentials.
@end deftypefun

@subheading gnutls_certificate_free_keys
@anchor{gnutls_certificate_free_keys}
@deftypefun {void} {gnutls_certificate_free_keys} (gnutls_certificate_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_certificate_credentials_t}  type.

This function will delete all the keys and the certificates associated
with the given credentials. This function must not be called when a
TLS negotiation that uses the credentials is in progress.
@end deftypefun

@subheading gnutls_certificate_get_crt_raw
@anchor{gnutls_certificate_get_crt_raw}
@deftypefun {int} {gnutls_certificate_get_crt_raw} (gnutls_certificate_credentials_t @var{sc}, unsigned @var{idx1}, unsigned @var{idx2}, gnutls_datum_t * @var{cert})
@var{sc}: is a @code{gnutls_certificate_credentials_t}  type.

@var{idx1}: the index of the certificate chain if multiple are present

@var{idx2}: the index of the certificate in the chain. Zero gives the server's certificate.

@var{cert}: Will hold the DER encoded certificate.

This function will return the DER encoded certificate of the
server or any other certificate on its certificate chain (based on  @code{idx2} ).
The returned data should be treated as constant and only accessible during the lifetime
of  @code{sc} . The  @code{idx1} matches the value @code{gnutls_certificate_set_x509_key()}  and friends
functions.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a
negative error value. In case the indexes are out of bounds @code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE} 
is returned.

@strong{Since:} 3.2.5
@end deftypefun

@subheading gnutls_certificate_get_issuer
@anchor{gnutls_certificate_get_issuer}
@deftypefun {int} {gnutls_certificate_get_issuer} (gnutls_certificate_credentials_t @var{sc}, gnutls_x509_crt_t @var{cert}, gnutls_x509_crt_t * @var{issuer}, unsigned int @var{flags})
@var{sc}: is a @code{gnutls_certificate_credentials_t}  type.

@var{cert}: is the certificate to find issuer for

@var{issuer}: Will hold the issuer if any. Should be treated as constant.

@var{flags}: Use zero or @code{GNUTLS_TL_GET_COPY} 

This function will return the issuer of a given certificate.
If the flag @code{GNUTLS_TL_GET_COPY}  is specified a copy of the issuer
will be returned which must be freed using @code{gnutls_x509_crt_deinit()} .
In that case the provided  @code{issuer} must not be initialized.

As with @code{gnutls_x509_trust_list_get_issuer()}  this function requires
the @code{GNUTLS_TL_GET_COPY}  flag in order to operate with PKCS@code{11}  trust
lists in a thread-safe way.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a
negative error value.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_certificate_get_ocsp_expiration
@anchor{gnutls_certificate_get_ocsp_expiration}
@deftypefun {time_t} {gnutls_certificate_get_ocsp_expiration} (gnutls_certificate_credentials_t @var{sc}, unsigned @var{idx}, int @var{oidx}, unsigned @var{flags})
@var{sc}: is a credentials structure.

@var{idx}: is a certificate chain index as returned by @code{gnutls_certificate_set_key()}  and friends

@var{oidx}: is an OCSP response index

@var{flags}: should be zero

This function returns the validity of the loaded OCSP responses,
to provide information on when to reload/refresh them.

Note that the credentials structure should be read-only when in
use, thus when reloading, either the credentials structure must not
be in use by any sessions, or a new credentials structure should be
allocated for new sessions.

When  @code{oidx} is (-1) then the minimum refresh time for all responses
is returned. Otherwise the index specifies the response corresponding
to the  @code{odix} certificate in the certificate chain.

@strong{Returns:} On success, the expiration time of the OCSP response. Otherwise
(time_t)(-1) on error, or (time_t)-2 on out of bounds.

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_certificate_get_ours
@anchor{gnutls_certificate_get_ours}
@deftypefun {const gnutls_datum_t *} {gnutls_certificate_get_ours} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

Gets the certificate as sent to the peer in the last handshake.
The certificate is in raw (DER) format.  No certificate
list is being returned. Only the first certificate.

This function returns the certificate that was sent in the current
handshake. In subsequent resumed sessions this function will return
@code{NULL} . That differs from @code{gnutls_certificate_get_peers()}  which always
returns the peer's certificate used in the original session.

@strong{Returns:} a pointer to a @code{gnutls_datum_t}  containing our
certificate, or @code{NULL}  in case of an error or if no certificate
was used.
@end deftypefun

@subheading gnutls_certificate_get_peers
@anchor{gnutls_certificate_get_peers}
@deftypefun {const gnutls_datum_t *} {gnutls_certificate_get_peers} (gnutls_session_t          @var{session}, unsigned int * @var{list_size})
@var{session}: is a gnutls session

@var{list_size}: is the length of the certificate list (may be @code{NULL} )

Get the peer's raw certificate (chain) as sent by the peer.  These
certificates are in raw format (DER encoded for X.509).  In case of
a X.509 then a certificate list may be present.  The list
is provided as sent by the server; the server must send as first
certificate in the list its own certificate, following the
issuer's certificate, then the issuer's issuer etc. However, there
are servers which violate this principle and thus on certain
occasions this may be an unsorted list.

In resumed sessions, this function will return the peer's certificate
list as used in the first/original session.

@strong{Returns:} a pointer to a @code{gnutls_datum_t}  containing the peer's
certificates, or @code{NULL}  in case of an error or if no certificate
was used.
@end deftypefun

@subheading gnutls_certificate_get_peers_subkey_id
@anchor{gnutls_certificate_get_peers_subkey_id}
@deftypefun {int} {gnutls_certificate_get_peers_subkey_id} (gnutls_session_t @var{session}, gnutls_datum_t * @var{id})
@var{session}: is a gnutls session

@var{id}: will contain the ID

This function is no-op.

@strong{Returns:} @code{GNUTLS_E_UNIMPLEMENTED_FEATURE} .

@strong{Since:} 3.1.3
@end deftypefun

@subheading gnutls_certificate_get_verify_flags
@anchor{gnutls_certificate_get_verify_flags}
@deftypefun {unsigned int} {gnutls_certificate_get_verify_flags} (gnutls_certificate_credentials_t @var{res})
@var{res}: is a gnutls_certificate_credentials_t type

Returns the verification flags set with
@code{gnutls_certificate_set_verify_flags()} .

@strong{Returns:} The certificate verification flags used by  @code{res} .

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_certificate_get_x509_crt
@anchor{gnutls_certificate_get_x509_crt}
@deftypefun {int} {gnutls_certificate_get_x509_crt} (gnutls_certificate_credentials_t @var{res}, unsigned @var{index}, gnutls_x509_crt_t ** @var{crt_list}, unsigned * @var{crt_list_size})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{index}: The index of the certificate list to obtain.

@var{crt_list}: Where to store the certificate list.

@var{crt_list_size}: Will hold the number of certificates.

Obtains a X.509 certificate list that has been stored in  @code{res} with one of
@code{gnutls_certificate_set_x509_key()} , @code{gnutls_certificate_set_key()} ,
@code{gnutls_certificate_set_x509_key_file()} ,
@code{gnutls_certificate_set_x509_key_file2()} ,
@code{gnutls_certificate_set_x509_key_mem()} , or
@code{gnutls_certificate_set_x509_key_mem2()} . Each certificate in the returned
certificate list must be deallocated with @code{gnutls_x509_crt_deinit()} , and the
list itself must be freed with @code{gnutls_free()} .

The  @code{index} matches the return value of @code{gnutls_certificate_set_x509_key()}  and friends
functions, when the @code{GNUTLS_CERTIFICATE_API_V2}  flag is set.

If there is no certificate with the given index,
@code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE}  is returned. If the certificate
with the given index is not a X.509 certificate, @code{GNUTLS_E_INVALID_REQUEST} 
is returned. The returned certificates must be deinitialized after
use, and the  @code{crt_list} pointer must be freed using @code{gnutls_free()} .

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  (0) on success, or a negative error code.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_certificate_get_x509_key
@anchor{gnutls_certificate_get_x509_key}
@deftypefun {int} {gnutls_certificate_get_x509_key} (gnutls_certificate_credentials_t @var{res}, unsigned @var{index}, gnutls_x509_privkey_t * @var{key})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{index}: The index of the key to obtain.

@var{key}: Location to store the key.

Obtains a X.509 private key that has been stored in  @code{res} with one of
@code{gnutls_certificate_set_x509_key()} , @code{gnutls_certificate_set_key()} ,
@code{gnutls_certificate_set_x509_key_file()} ,
@code{gnutls_certificate_set_x509_key_file2()} ,
@code{gnutls_certificate_set_x509_key_mem()} , or
@code{gnutls_certificate_set_x509_key_mem2()} . The returned key must be deallocated
with @code{gnutls_x509_privkey_deinit()}  when no longer needed.

The  @code{index} matches the return value of @code{gnutls_certificate_set_x509_key()}  and friends
functions, when the @code{GNUTLS_CERTIFICATE_API_V2}  flag is set.

If there is no key with the given index,
@code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE}  is returned. If the key with the
given index is not a X.509 key, @code{GNUTLS_E_INVALID_REQUEST}  is returned.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  (0) on success, or a negative error code.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_certificate_send_x509_rdn_sequence
@anchor{gnutls_certificate_send_x509_rdn_sequence}
@deftypefun {void} {gnutls_certificate_send_x509_rdn_sequence} (gnutls_session_t @var{session}, int @var{status})
@var{session}: a @code{gnutls_session_t}  type.

@var{status}: is 0 or 1

If status is non zero, this function will order gnutls not to send
the rdnSequence in the certificate request message. That is the
server will not advertise its trusted CAs to the peer. If status
is zero then the default behaviour will take effect, which is to
advertise the server's trusted CAs.

This function has no effect in clients, and in authentication
methods other than certificate with X.509 certificates.
@end deftypefun

@subheading gnutls_certificate_server_set_request
@anchor{gnutls_certificate_server_set_request}
@deftypefun {void} {gnutls_certificate_server_set_request} (gnutls_session_t @var{session}, gnutls_certificate_request_t @var{req})
@var{session}: is a @code{gnutls_session_t}  type.

@var{req}: is one of GNUTLS_CERT_REQUEST, GNUTLS_CERT_REQUIRE, GNUTLS_CERT_IGNORE

This function specifies if we (in case of a server) are going to
send a certificate request message to the client. If  @code{req} is
GNUTLS_CERT_REQUIRE then the server will return the @code{GNUTLS_E_NO_CERTIFICATE_FOUND} 
error if the peer does not provide a certificate. If you do not call this
function then the client will not be asked to send a certificate. Invoking
the function with  @code{req} GNUTLS_CERT_IGNORE has the same effect.
@end deftypefun

@subheading gnutls_certificate_set_dh_params
@anchor{gnutls_certificate_set_dh_params}
@deftypefun {void} {gnutls_certificate_set_dh_params} (gnutls_certificate_credentials_t @var{res}, gnutls_dh_params_t @var{dh_params})
@var{res}: is a gnutls_certificate_credentials_t type

@var{dh_params}: the Diffie-Hellman parameters.

This function will set the Diffie-Hellman parameters for a
certificate server to use. These parameters will be used in
Ephemeral Diffie-Hellman cipher suites.  Note that only a pointer
to the parameters are stored in the certificate handle, so you
must not deallocate the parameters before the certificate is deallocated.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.
@end deftypefun

@subheading gnutls_certificate_set_flags
@anchor{gnutls_certificate_set_flags}
@deftypefun {void} {gnutls_certificate_set_flags} (gnutls_certificate_credentials_t @var{res}, unsigned int @var{flags})
@var{res}: is a gnutls_certificate_credentials_t type

@var{flags}: are the flags of @code{gnutls_certificate_flags}  type

This function will set flags to tweak the operation of
the credentials structure. See the @code{gnutls_certificate_flags}  enumerations
for more information on the available flags. 

@strong{Since:} 3.4.7
@end deftypefun

@subheading gnutls_certificate_set_known_dh_params
@anchor{gnutls_certificate_set_known_dh_params}
@deftypefun {int} {gnutls_certificate_set_known_dh_params} (gnutls_certificate_credentials_t @var{res}, gnutls_sec_param_t @var{sec_param})
@var{res}: is a gnutls_certificate_credentials_t type

@var{sec_param}: is an option of the @code{gnutls_sec_param_t}  enumeration

This function will set the Diffie-Hellman parameters for a
certificate server to use. These parameters will be used in
Ephemeral Diffie-Hellman cipher suites and will be selected from
the FFDHE set of RFC7919 according to the security level provided.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a
negative error value.

@strong{Since:} 3.5.6
@end deftypefun

@subheading gnutls_certificate_set_ocsp_status_request_file
@anchor{gnutls_certificate_set_ocsp_status_request_file}
@deftypefun {int} {gnutls_certificate_set_ocsp_status_request_file} (gnutls_certificate_credentials_t @var{sc}, const char * @var{response_file}, unsigned @var{idx})
@var{sc}: is a credentials structure.

@var{response_file}: a filename of the OCSP response

@var{idx}: is a certificate index as returned by @code{gnutls_certificate_set_key()}  and friends

This function loads the provided OCSP response. It will be
sent to the client if requests an OCSP certificate status for
the certificate chain specified by  @code{idx} .

@strong{Note:} the ability to set multiple OCSP responses per credential
structure via the index  @code{idx} was added in version 3.5.6. To keep
backwards compatibility, it requires using @code{gnutls_certificate_set_flags()} 
with the @code{GNUTLS_CERTIFICATE_API_V2}  flag to make the set certificate
functions return an index usable by this function.

This function can be called multiple times since GnuTLS 3.6.3
when multiple responses which apply to the chain are available.
If the response provided does not match any certificates present
in the chain, the code @code{GNUTLS_E_OCSP_MISMATCH_WITH_CERTS}  is returned.
To revert to the previous behavior set the flag @code{GNUTLS_CERTIFICATE_SKIP_OCSP_RESPONSE_CHECK} 
in the certificate credentials structure. In that case, only the
end-certificate's OCSP response can be set.
If the response is already expired at the time of loading the code
@code{GNUTLS_E_EXPIRED}  is returned.

To revert to the previous behavior of this function which does not return
any errors, set the flag @code{GNUTLS_CERTIFICATE_SKIP_OCSP_RESPONSE_CHECK} 

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

@strong{Since:} 3.1.3
@end deftypefun

@subheading gnutls_certificate_set_ocsp_status_request_file2
@anchor{gnutls_certificate_set_ocsp_status_request_file2}
@deftypefun {int} {gnutls_certificate_set_ocsp_status_request_file2} (gnutls_certificate_credentials_t @var{sc}, const char * @var{response_file}, unsigned @var{idx}, gnutls_x509_crt_fmt_t @var{fmt})
@var{sc}: is a credentials structure.

@var{response_file}: a filename of the OCSP response

@var{idx}: is a certificate index as returned by @code{gnutls_certificate_set_key()}  and friends

@var{fmt}: is PEM or DER

This function loads the OCSP responses to be sent to the
peer for the certificate chain specified by  @code{idx} . When  @code{fmt} is
set to PEM, multiple responses can be loaded.

This function must be called after setting any certificates, and
cannot be used for certificates that are provided via a callback --
that is when @code{gnutls_certificate_set_retrieve_function()}  is used. In
that case consider using @code{gnutls_certificate_set_retrieve_function3()} .

This function can be called multiple times when multiple responses
applicable to the certificate chain are available.
If the response provided does not match any certificates present
in the chain, the code @code{GNUTLS_E_OCSP_MISMATCH_WITH_CERTS}  is returned.
If the response is already expired at the time of loading the code
@code{GNUTLS_E_EXPIRED}  is returned.

@strong{Returns:} On success, the number of loaded responses is returned,
otherwise a negative error code.

@strong{Since:} 3.1.3
@end deftypefun

@subheading gnutls_certificate_set_ocsp_status_request_function
@anchor{gnutls_certificate_set_ocsp_status_request_function}
@deftypefun {void} {gnutls_certificate_set_ocsp_status_request_function} (gnutls_certificate_credentials_t @var{sc}, gnutls_status_request_ocsp_func @var{ocsp_func}, void * @var{ptr})
@var{sc}: is a @code{gnutls_certificate_credentials_t}  type.

@var{ocsp_func}: function pointer to OCSP status request callback.

@var{ptr}: opaque pointer passed to callback function

This function is to be used by server to register a callback to
handle OCSP status requests from the client.  The callback will be
invoked if the client supplied a status-request OCSP extension.
The callback function prototype is:

typedef int (*gnutls_status_request_ocsp_func)
(gnutls_session_t session, void *ptr, gnutls_datum_t *ocsp_response);

The callback will be invoked if the client requests an OCSP certificate
status.  The callback may return @code{GNUTLS_E_NO_CERTIFICATE_STATUS} , if
there is no recent OCSP response. If the callback returns @code{GNUTLS_E_SUCCESS} ,
it is expected to have the  @code{ocsp_response} field set with a valid (DER-encoded)
OCSP response. The response must be a value allocated using @code{gnutls_malloc()} ,
and will be deinitialized by the caller.

It is possible to set a specific callback for each provided certificate
using @code{gnutls_certificate_set_ocsp_status_request_function2()} .

@strong{Since:} 3.1.3
@end deftypefun

@subheading gnutls_certificate_set_ocsp_status_request_function2
@anchor{gnutls_certificate_set_ocsp_status_request_function2}
@deftypefun {int} {gnutls_certificate_set_ocsp_status_request_function2} (gnutls_certificate_credentials_t @var{sc}, unsigned @var{idx}, gnutls_status_request_ocsp_func @var{ocsp_func}, void * @var{ptr})
@var{sc}: is a @code{gnutls_certificate_credentials_t}  type.

@var{idx}: is a certificate index as returned by @code{gnutls_certificate_set_key()}  and friends

@var{ocsp_func}: function pointer to OCSP status request callback.

@var{ptr}: opaque pointer passed to callback function

This function is to be used by server to register a callback to
provide OCSP status requests that correspond to the indexed certificate chain
from the client.  The callback will be invoked if the client supplied a
status-request OCSP extension.

The callback function prototype is:

typedef int (*gnutls_status_request_ocsp_func)
(gnutls_session_t session, void *ptr, gnutls_datum_t *ocsp_response);

The callback will be invoked if the client requests an OCSP certificate
status.  The callback may return @code{GNUTLS_E_NO_CERTIFICATE_STATUS} , if
there is no recent OCSP response. If the callback returns @code{GNUTLS_E_SUCCESS} ,
it is expected to have the  @code{ocsp_response} field set with a valid (DER-encoded)
OCSP response. The response must be a value allocated using @code{gnutls_malloc()} ,
and will be deinitialized by the caller.

@strong{Note:} the ability to set multiple OCSP responses per credential
structure via the index  @code{idx} was added in version 3.5.6. To keep
backwards compatibility, it requires using @code{gnutls_certificate_set_flags()} 
with the @code{GNUTLS_CERTIFICATE_API_V2}  flag to make the set certificate
functions return an index usable by this function.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

@strong{Since:} 3.5.5
@end deftypefun

@subheading gnutls_certificate_set_ocsp_status_request_mem
@anchor{gnutls_certificate_set_ocsp_status_request_mem}
@deftypefun {int} {gnutls_certificate_set_ocsp_status_request_mem} (gnutls_certificate_credentials_t @var{sc}, const gnutls_datum_t * @var{resp_data}, unsigned @var{idx}, gnutls_x509_crt_fmt_t @var{fmt})
@var{sc}: is a credentials structure.

@var{resp_data}: a memory buffer holding an OCSP response

@var{idx}: is a certificate index as returned by @code{gnutls_certificate_set_key()}  and friends

@var{fmt}: is PEM or DER

This function sets the OCSP responses to be sent to the
peer for the certificate chain specified by  @code{idx} . When  @code{fmt} is set
to PEM, multiple responses can be loaded.

@strong{Note:} the ability to set multiple OCSP responses per credential
structure via the index  @code{idx} was added in version 3.5.6. To keep
backwards compatibility, it requires using @code{gnutls_certificate_set_flags()} 
with the @code{GNUTLS_CERTIFICATE_API_V2}  flag to make the set certificate
functions return an index usable by this function.

This function must be called after setting any certificates, and
cannot be used for certificates that are provided via a callback --
that is when @code{gnutls_certificate_set_retrieve_function()}  is used.

This function can be called multiple times when multiple responses which
apply to the certificate chain are available.
If the response provided does not match any certificates present
in the chain, the code @code{GNUTLS_E_OCSP_MISMATCH_WITH_CERTS}  is returned.
If the response is already expired at the time of loading the code
@code{GNUTLS_E_EXPIRED}  is returned.

@strong{Returns:} On success, the number of loaded responses is returned,
otherwise a negative error code.

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_certificate_set_params_function
@anchor{gnutls_certificate_set_params_function}
@deftypefun {void} {gnutls_certificate_set_params_function} (gnutls_certificate_credentials_t            @var{res}, gnutls_params_function * @var{func})
@var{res}: is a gnutls_certificate_credentials_t type

@var{func}: is the function to be called

This function will set a callback in order for the server to get
the Diffie-Hellman or RSA parameters for certificate
authentication.  The callback should return @code{GNUTLS_E_SUCCESS}  (0) on success.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.
@end deftypefun

@subheading gnutls_certificate_set_pin_function
@anchor{gnutls_certificate_set_pin_function}
@deftypefun {void} {gnutls_certificate_set_pin_function} (gnutls_certificate_credentials_t       @var{cred}, gnutls_pin_callback_t @var{fn}, void * @var{userdata})
@var{cred}: is a @code{gnutls_certificate_credentials_t}  type.

@var{fn}: A PIN callback

@var{userdata}: Data to be passed in the callback

This function will set a callback function to be used when
required to access a protected object. This function overrides any other
global PIN functions.

Note that this function must be called right after initialization
to have effect.

@strong{Since:} 3.1.0
@end deftypefun

@subheading gnutls_certificate_set_rawpk_key_file
@anchor{gnutls_certificate_set_rawpk_key_file}
@deftypefun {int} {gnutls_certificate_set_rawpk_key_file} (gnutls_certificate_credentials_t @var{cred}, const char* @var{rawpkfile}, const char* @var{privkeyfile}, gnutls_x509_crt_fmt_t @var{format}, const char * @var{pass}, unsigned int @var{key_usage}, const char ** @var{names}, unsigned int @var{names_length}, unsigned int @var{privkey_flags}, unsigned int @var{pkcs11_flags})
@var{cred}: is a @code{gnutls_certificate_credentials_t}  type.

@var{rawpkfile}: contains a raw public key in
PKIX.SubjectPublicKeyInfo format.

@var{privkeyfile}: contains a file path to a private key.

@var{format}: encoding of the keys. DER or PEM.

@var{pass}: an optional password to unlock the private key privkeyfile.

@var{key_usage}: an ORed sequence of @code{GNUTLS_KEY_} * flags.

@var{names}: is an array of DNS names belonging to the public-key (NULL if none).

@var{names_length}: holds the length of the names list.

@var{privkey_flags}: an ORed sequence of @code{gnutls_pkcs_encrypt_flags_t} .
These apply to the private key pkey.

@var{pkcs11_flags}: one of gnutls_pkcs11_obj_flags. These apply to URLs.

This function sets a public/private keypair read from file in the
@code{gnutls_certificate_credentials_t}  type to be used for authentication
and/or encryption.  @code{spki} and  @code{privkey} should match otherwise set
signatures cannot be validated. In case of no match this function
returns @code{GNUTLS_E_CERTIFICATE_KEY_MISMATCH} . This function should
be called once for the client because there is currently no mechanism
to determine which raw public-key to select for the peer when there
are multiple present. Multiple raw public keys for the server can be
distinghuished by setting the  @code{names} .

Note here that  @code{spki} is a raw public-key as defined
in RFC7250. It means that there is no surrounding certificate that
holds the public key and that there is therefore no direct mechanism
to prove the authenticity of this key. The keypair can be used during
a TLS handshake but its authenticity should be established via a
different mechanism (e.g. TOFU or known fingerprint).

The supported formats are basic unencrypted key, PKCS8, PKCS12,
and the openssl format and will be autodetected.

If the raw public-key and the private key are given in PEM encoding
then the strings that hold their values must be null terminated.

Key usage (as defined by X.509 extension (2.5.29.15)) can be explicitly
set because there is no certificate structure around the key to define
this value. See for more info @code{gnutls_x509_crt_get_key_usage()} .

Note that, this function by default returns zero on success and a
negative value on error. Since 3.5.6, when the flag @code{GNUTLS_CERTIFICATE_API_V2} 
is set using @code{gnutls_certificate_set_flags()}  it returns an index
(greater or equal to zero). That index can be used in other functions
to refer to the added key-pair.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, in case the
key pair does not match @code{GNUTLS_E_CERTIFICATE_KEY_MISMATCH}  is returned,
in other erroneous cases a different negative error code is returned.

@strong{Since:} 3.6.6
@end deftypefun

@subheading gnutls_certificate_set_rawpk_key_mem
@anchor{gnutls_certificate_set_rawpk_key_mem}
@deftypefun {int} {gnutls_certificate_set_rawpk_key_mem} (gnutls_certificate_credentials_t @var{cred}, const gnutls_datum_t* @var{spki}, const gnutls_datum_t* @var{pkey}, gnutls_x509_crt_fmt_t @var{format}, const char* @var{pass}, unsigned int @var{key_usage}, const char ** @var{names}, unsigned int @var{names_length}, unsigned int @var{flags})
@var{cred}: is a @code{gnutls_certificate_credentials_t}  type.

@var{spki}: contains a raw public key in
PKIX.SubjectPublicKeyInfo format.

@var{pkey}: contains a raw private key.

@var{format}: encoding of the keys. DER or PEM.

@var{pass}: an optional password to unlock the private key pkey.

@var{key_usage}: An ORed sequence of @code{GNUTLS_KEY_} * flags.

@var{names}: is an array of DNS names belonging to the public-key (NULL if none).

@var{names_length}: holds the length of the names list.

@var{flags}: an ORed sequence of @code{gnutls_pkcs_encrypt_flags_t} .
These apply to the private key pkey.

This function sets a public/private keypair in the
@code{gnutls_certificate_credentials_t}  type to be used for authentication
and/or encryption.  @code{spki} and  @code{privkey} should match otherwise set
signatures cannot be validated. In case of no match this function
returns @code{GNUTLS_E_CERTIFICATE_KEY_MISMATCH} . This function should
be called once for the client because there is currently no mechanism
to determine which raw public-key to select for the peer when there
are multiple present. Multiple raw public keys for the server can be
distinghuished by setting the  @code{names} .

Note here that  @code{spki} is a raw public-key as defined
in RFC7250. It means that there is no surrounding certificate that
holds the public key and that there is therefore no direct mechanism
to prove the authenticity of this key. The keypair can be used during
a TLS handshake but its authenticity should be established via a
different mechanism (e.g. TOFU or known fingerprint).

The supported formats are basic unencrypted key, PKCS8, PKCS12,
and the openssl format and will be autodetected.

If the raw public-key and the private key are given in PEM encoding
then the strings that hold their values must be null terminated.

Key usage (as defined by X.509 extension (2.5.29.15)) can be explicitly
set because there is no certificate structure around the key to define
this value. See for more info @code{gnutls_x509_crt_get_key_usage()} .

Note that, this function by default returns zero on success and a
negative value on error. Since 3.5.6, when the flag @code{GNUTLS_CERTIFICATE_API_V2} 
is set using @code{gnutls_certificate_set_flags()}  it returns an index
(greater or equal to zero). That index can be used in other functions
to refer to the added key-pair.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, in case the
key pair does not match @code{GNUTLS_E_CERTIFICATE_KEY_MISMATCH}  is returned,
in other erroneous cases a different negative error code is returned.

@strong{Since:} 3.6.6
@end deftypefun

@subheading gnutls_certificate_set_retrieve_function
@anchor{gnutls_certificate_set_retrieve_function}
@deftypefun {void} {gnutls_certificate_set_retrieve_function} (gnutls_certificate_credentials_t @var{cred}, gnutls_certificate_retrieve_function * @var{func})
@var{cred}: is a @code{gnutls_certificate_credentials_t}  type.

@var{func}: is the callback function

This function sets a callback to be called in order to retrieve the
certificate to be used in the handshake. The callback will take control
only if a certificate is requested by the peer. You are advised
to use @code{gnutls_certificate_set_retrieve_function2()}  because it
is much more efficient in the processing it requires from gnutls.

The callback's function prototype is:
int (*callback)(gnutls_session_t, const gnutls_datum_t* req_ca_dn, int nreqs,
const gnutls_pk_algorithm_t* pk_algos, int pk_algos_length, gnutls_retr2_st* st);

 @code{req_ca_dn} is only used in X.509 certificates.
Contains a list with the CA names that the server considers trusted.
This is a hint and typically the client should send a certificate that is signed
by one of these CAs. These names, when available, are DER encoded. To get a more
meaningful value use the function @code{gnutls_x509_rdn_get()} .

 @code{pk_algos} contains a list with server's acceptable public key algorithms.
The certificate returned should support the server's given algorithms.

 @code{st} should contain the certificates and private keys.

If the callback function is provided then gnutls will call it, in the
handshake, after the certificate request message has been received.

In server side pk_algos and req_ca_dn are NULL.

The callback function should set the certificate list to be sent,
and return 0 on success. If no certificate was selected then the
number of certificates should be set to zero. The value (-1)
indicates error and the handshake will be terminated. If both certificates
are set in the credentials and a callback is available, the callback
takes predence.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_certificate_set_verify_flags
@anchor{gnutls_certificate_set_verify_flags}
@deftypefun {void} {gnutls_certificate_set_verify_flags} (gnutls_certificate_credentials_t         @var{res}, unsigned int @var{flags})
@var{res}: is a gnutls_certificate_credentials_t type

@var{flags}: are the flags

This function will set the flags to be used for verification 
of certificates and override any defaults.  The provided flags must be an OR of the
@code{gnutls_certificate_verify_flags}  enumerations. 
@end deftypefun

@subheading gnutls_certificate_set_verify_function
@anchor{gnutls_certificate_set_verify_function}
@deftypefun {void} {gnutls_certificate_set_verify_function} (gnutls_certificate_credentials_t @var{cred}, gnutls_certificate_verify_function * @var{func})
@var{cred}: is a @code{gnutls_certificate_credentials_t}  type.

@var{func}: is the callback function

This function sets a callback to be called when peer's certificate
has been received in order to verify it on receipt rather than
doing after the handshake is completed.

The callback's function prototype is:
int (*callback)(gnutls_session_t);

If the callback function is provided then gnutls will call it, in the
handshake, just after the certificate message has been received.
To verify or obtain the certificate the @code{gnutls_certificate_verify_peers2()} ,
@code{gnutls_certificate_type_get()} , @code{gnutls_certificate_get_peers()}  functions
can be used.

The callback function should return 0 for the handshake to continue
or non-zero to terminate.

@strong{Since:} 2.10.0
@end deftypefun

@subheading gnutls_certificate_set_verify_limits
@anchor{gnutls_certificate_set_verify_limits}
@deftypefun {void} {gnutls_certificate_set_verify_limits} (gnutls_certificate_credentials_t @var{res}, unsigned int @var{max_bits}, unsigned int @var{max_depth})
@var{res}: is a gnutls_certificate_credentials type

@var{max_bits}: is the number of bits of an acceptable certificate (default 8200)

@var{max_depth}: is maximum depth of the verification of a certificate chain (default 5)

This function will set some upper limits for the default
verification function, @code{gnutls_certificate_verify_peers2()} , to avoid
denial of service attacks.  You can set them to zero to disable
limits.
@end deftypefun

@subheading gnutls_certificate_set_x509_crl
@anchor{gnutls_certificate_set_x509_crl}
@deftypefun {int} {gnutls_certificate_set_x509_crl} (gnutls_certificate_credentials_t @var{res}, gnutls_x509_crl_t * @var{crl_list}, int @var{crl_list_size})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{crl_list}: is a list of trusted CRLs. They should have been verified before.

@var{crl_list_size}: holds the size of the crl_list

This function adds the trusted CRLs in order to verify client or
server certificates.  In case of a client this is not required to
be called if the certificates are not verified using
@code{gnutls_certificate_verify_peers2()} .  This function may be called
multiple times.

@strong{Returns:} number of CRLs processed, or a negative error code on error.

@strong{Since:} 2.4.0
@end deftypefun

@subheading gnutls_certificate_set_x509_crl_file
@anchor{gnutls_certificate_set_x509_crl_file}
@deftypefun {int} {gnutls_certificate_set_x509_crl_file} (gnutls_certificate_credentials_t @var{res}, const char * @var{crlfile}, gnutls_x509_crt_fmt_t @var{type})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{crlfile}: is a file containing the list of verified CRLs (DER or PEM list)

@var{type}: is PEM or DER

This function adds the trusted CRLs in order to verify client or server
certificates.  In case of a client this is not required
to be called if the certificates are not verified using
@code{gnutls_certificate_verify_peers2()} .
This function may be called multiple times.

@strong{Returns:} number of CRLs processed or a negative error code on error.
@end deftypefun

@subheading gnutls_certificate_set_x509_crl_mem
@anchor{gnutls_certificate_set_x509_crl_mem}
@deftypefun {int} {gnutls_certificate_set_x509_crl_mem} (gnutls_certificate_credentials_t @var{res}, const gnutls_datum_t * @var{CRL}, gnutls_x509_crt_fmt_t @var{type})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{CRL}: is a list of trusted CRLs. They should have been verified before.

@var{type}: is DER or PEM

This function adds the trusted CRLs in order to verify client or
server certificates.  In case of a client this is not required to
be called if the certificates are not verified using
@code{gnutls_certificate_verify_peers2()} .  This function may be called
multiple times.

@strong{Returns:} number of CRLs processed, or a negative error code on error.
@end deftypefun

@subheading gnutls_certificate_set_x509_key
@anchor{gnutls_certificate_set_x509_key}
@deftypefun {int} {gnutls_certificate_set_x509_key} (gnutls_certificate_credentials_t @var{res}, gnutls_x509_crt_t * @var{cert_list}, int @var{cert_list_size}, gnutls_x509_privkey_t @var{key})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{cert_list}: contains a certificate list (path) for the specified private key

@var{cert_list_size}: holds the size of the certificate list

@var{key}: is a @code{gnutls_x509_privkey_t}  key

This function sets a certificate/private key pair in the
gnutls_certificate_credentials_t type.  This function may be
called more than once, in case multiple keys/certificates exist for
the server.  For clients that wants to send more than their own end
entity certificate (e.g., also an intermediate CA cert) then put
the certificate chain in  @code{cert_list} .

Note that the certificates and keys provided, can be safely deinitialized
after this function is called.

If that function fails to load the  @code{res} type is at an undefined state, it must
not be reused to load other keys or certificates.

Note that, this function by default returns zero on success and a negative value on error.
Since 3.5.6, when the flag @code{GNUTLS_CERTIFICATE_API_V2}  is set using @code{gnutls_certificate_set_flags()} 
it returns an index (greater or equal to zero). That index can be used to other functions to refer to the added key-pair.

@strong{Returns:} On success this functions returns zero, and otherwise a negative value on error (see above for modifying that behavior).

@strong{Since:} 2.4.0
@end deftypefun

@subheading gnutls_certificate_set_x509_key_file
@anchor{gnutls_certificate_set_x509_key_file}
@deftypefun {int} {gnutls_certificate_set_x509_key_file} (gnutls_certificate_credentials_t @var{res}, const char * @var{certfile}, const char * @var{keyfile}, gnutls_x509_crt_fmt_t @var{type})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{certfile}: is a file that containing the certificate list (path) for
the specified private key, in PKCS7 format, or a list of certificates

@var{keyfile}: is a file that contains the private key

@var{type}: is PEM or DER

This function sets a certificate/private key pair in the
gnutls_certificate_credentials_t type.  This function may be
called more than once, in case multiple keys/certificates exist for
the server.  For clients that need to send more than its own end
entity certificate, e.g., also an intermediate CA cert, then the
 @code{certfile} must contain the ordered certificate chain.

Note that the names in the certificate provided will be considered
when selecting the appropriate certificate to use (in case of multiple
certificate/key pairs).

This function can also accept URLs at  @code{keyfile} and  @code{certfile} . In that case it
will use the private key and certificate indicated by the URLs. Note
that the supported URLs are the ones indicated by @code{gnutls_url_is_supported()} .

In case the  @code{certfile} is provided as a PKCS @code{11}  URL, then the certificate, and its
present issuers in the token are imported (i.e., forming the required trust chain).

If that function fails to load the  @code{res} structure is at an undefined state, it must
not be reused to load other keys or certificates.

Note that, this function by default returns zero on success and a negative value on error.
Since 3.5.6, when the flag @code{GNUTLS_CERTIFICATE_API_V2}  is set using @code{gnutls_certificate_set_flags()} 
it returns an index (greater or equal to zero). That index can be used to other functions to refer to the added key-pair.

@strong{Returns:} On success this functions returns zero, and otherwise a negative value on error (see above for modifying that behavior).

@strong{Since:} 3.1.11
@end deftypefun

@subheading gnutls_certificate_set_x509_key_file2
@anchor{gnutls_certificate_set_x509_key_file2}
@deftypefun {int} {gnutls_certificate_set_x509_key_file2} (gnutls_certificate_credentials_t @var{res}, const char * @var{certfile}, const char * @var{keyfile}, gnutls_x509_crt_fmt_t @var{type}, const char * @var{pass}, unsigned int @var{flags})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{certfile}: is a file that containing the certificate list (path) for
the specified private key, in PKCS7 format, or a list of certificates

@var{keyfile}: is a file that contains the private key

@var{type}: is PEM or DER

@var{pass}: is the password of the key

@var{flags}: an ORed sequence of gnutls_pkcs_encrypt_flags_t

This function sets a certificate/private key pair in the
gnutls_certificate_credentials_t type.  This function may be
called more than once, in case multiple keys/certificates exist for
the server.  For clients that need to send more than its own end
entity certificate, e.g., also an intermediate CA cert, then the
 @code{certfile} must contain the ordered certificate chain.

Note that the names in the certificate provided will be considered
when selecting the appropriate certificate to use (in case of multiple
certificate/key pairs).

This function can also accept URLs at  @code{keyfile} and  @code{certfile} . In that case it
will use the private key and certificate indicated by the URLs. Note
that the supported URLs are the ones indicated by @code{gnutls_url_is_supported()} .
Before GnuTLS 3.4.0 when a URL was specified, the  @code{pass} part was ignored and a
PIN callback had to be registered, this is no longer the case in current releases.

In case the  @code{certfile} is provided as a PKCS @code{11}  URL, then the certificate, and its
present issuers in the token are imported (i.e., forming the required trust chain).

If that function fails to load the  @code{res} structure is at an undefined state, it must
not be reused to load other keys or certificates.

Note that, this function by default returns zero on success and a negative value on error.
Since 3.5.6, when the flag @code{GNUTLS_CERTIFICATE_API_V2}  is set using @code{gnutls_certificate_set_flags()} 
it returns an index (greater or equal to zero). That index can be used to other functions to refer to the added key-pair.

@strong{Returns:} On success this functions returns zero, and otherwise a negative value on error (see above for modifying that behavior).
@end deftypefun

@subheading gnutls_certificate_set_x509_key_mem
@anchor{gnutls_certificate_set_x509_key_mem}
@deftypefun {int} {gnutls_certificate_set_x509_key_mem} (gnutls_certificate_credentials_t @var{res}, const gnutls_datum_t * @var{cert}, const gnutls_datum_t * @var{key}, gnutls_x509_crt_fmt_t @var{type})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{cert}: contains a certificate list (path) for the specified private key

@var{key}: is the private key, or @code{NULL} 

@var{type}: is PEM or DER

This function sets a certificate/private key pair in the
gnutls_certificate_credentials_t type. This function may be called
more than once, in case multiple keys/certificates exist for the
server.

Note that the keyUsage (2.5.29.15) PKIX extension in X.509 certificates
is supported. This means that certificates intended for signing cannot
be used for ciphersuites that require encryption.

If the certificate and the private key are given in PEM encoding
then the strings that hold their values must be null terminated.

The  @code{key} may be @code{NULL}  if you are using a sign callback, see
@code{gnutls_sign_callback_set()} .

Note that, this function by default returns zero on success and a negative value on error.
Since 3.5.6, when the flag @code{GNUTLS_CERTIFICATE_API_V2}  is set using @code{gnutls_certificate_set_flags()} 
it returns an index (greater or equal to zero). That index can be used to other functions to refer to the added key-pair.

@strong{Returns:} On success this functions returns zero, and otherwise a negative value on error (see above for modifying that behavior).
@end deftypefun

@subheading gnutls_certificate_set_x509_key_mem2
@anchor{gnutls_certificate_set_x509_key_mem2}
@deftypefun {int} {gnutls_certificate_set_x509_key_mem2} (gnutls_certificate_credentials_t @var{res}, const gnutls_datum_t * @var{cert}, const gnutls_datum_t * @var{key}, gnutls_x509_crt_fmt_t @var{type}, const char * @var{pass}, unsigned int @var{flags})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{cert}: contains a certificate list (path) for the specified private key

@var{key}: is the private key, or @code{NULL} 

@var{type}: is PEM or DER

@var{pass}: is the key's password

@var{flags}: an ORed sequence of gnutls_pkcs_encrypt_flags_t

This function sets a certificate/private key pair in the
gnutls_certificate_credentials_t type. This function may be called
more than once, in case multiple keys/certificates exist for the
server.

Note that the keyUsage (2.5.29.15) PKIX extension in X.509 certificates
is supported. This means that certificates intended for signing cannot
be used for ciphersuites that require encryption.

If the certificate and the private key are given in PEM encoding
then the strings that hold their values must be null terminated.

The  @code{key} may be @code{NULL}  if you are using a sign callback, see
@code{gnutls_sign_callback_set()} .

Note that, this function by default returns zero on success and a negative value on error.
Since 3.5.6, when the flag @code{GNUTLS_CERTIFICATE_API_V2}  is set using @code{gnutls_certificate_set_flags()} 
it returns an index (greater or equal to zero). That index can be used to other functions to refer to the added key-pair.

@strong{Returns:} On success this functions returns zero, and otherwise a negative value on error (see above for modifying that behavior).
@end deftypefun

@subheading gnutls_certificate_set_x509_simple_pkcs12_file
@anchor{gnutls_certificate_set_x509_simple_pkcs12_file}
@deftypefun {int} {gnutls_certificate_set_x509_simple_pkcs12_file} (gnutls_certificate_credentials_t @var{res}, const char * @var{pkcs12file}, gnutls_x509_crt_fmt_t @var{type}, const char * @var{password})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{pkcs12file}: filename of file containing PKCS@code{12}  blob.

@var{type}: is PEM or DER of the  @code{pkcs12file} .

@var{password}: optional password used to decrypt PKCS@code{12}  file, bags and keys.

This function sets a certificate/private key pair and/or a CRL in
the gnutls_certificate_credentials_t type.  This function may
be called more than once (in case multiple keys/certificates exist
for the server).

PKCS@code{12}  files with a MAC, encrypted bags and PKCS @code{8} 
private keys are supported. However,
only password based security, and the same password for all
operations, are supported.

PKCS@code{12}  file may contain many keys and/or certificates, and this
function will try to auto-detect based on the key ID the certificate
and key pair to use. If the PKCS@code{12}  file contain the issuer of
the selected certificate, it will be appended to the certificate
to form a chain.

If more than one private keys are stored in the PKCS@code{12}  file,
then only one key will be read (and it is undefined which one).

It is believed that the limitations of this function is acceptable
for most usage, and that any more flexibility would introduce
complexity that would make it harder to use this functionality at
all.

Note that, this function by default returns zero on success and a negative value on error.
Since 3.5.6, when the flag @code{GNUTLS_CERTIFICATE_API_V2}  is set using @code{gnutls_certificate_set_flags()} 
it returns an index (greater or equal to zero). That index can be used to other functions to refer to the added key-pair.

@strong{Returns:} On success this functions returns zero, and otherwise a negative value on error (see above for modifying that behavior).
@end deftypefun

@subheading gnutls_certificate_set_x509_simple_pkcs12_mem
@anchor{gnutls_certificate_set_x509_simple_pkcs12_mem}
@deftypefun {int} {gnutls_certificate_set_x509_simple_pkcs12_mem} (gnutls_certificate_credentials_t @var{res}, const gnutls_datum_t * @var{p12blob}, gnutls_x509_crt_fmt_t @var{type}, const char * @var{password})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{p12blob}: the PKCS@code{12}  blob.

@var{type}: is PEM or DER of the  @code{pkcs12file} .

@var{password}: optional password used to decrypt PKCS@code{12}  file, bags and keys.

This function sets a certificate/private key pair and/or a CRL in
the gnutls_certificate_credentials_t type.  This function may
be called more than once (in case multiple keys/certificates exist
for the server).

Encrypted PKCS@code{12}  bags and PKCS@code{8}  private keys are supported.  However,
only password based security, and the same password for all
operations, are supported.

PKCS@code{12}  file may contain many keys and/or certificates, and this
function will try to auto-detect based on the key ID the certificate
and key pair to use. If the PKCS@code{12}  file contain the issuer of
the selected certificate, it will be appended to the certificate
to form a chain.

If more than one private keys are stored in the PKCS@code{12}  file,
then only one key will be read (and it is undefined which one).

It is believed that the limitations of this function is acceptable
for most usage, and that any more flexibility would introduce
complexity that would make it harder to use this functionality at
all.

Note that, this function by default returns zero on success and a negative value on error.
Since 3.5.6, when the flag @code{GNUTLS_CERTIFICATE_API_V2}  is set using @code{gnutls_certificate_set_flags()} 
it returns an index (greater or equal to zero). That index can be used to other functions to refer to the added key-pair.

@strong{Returns:} On success this functions returns zero, and otherwise a negative value on error (see above for modifying that behavior).

@strong{Since:} 2.8.0
@end deftypefun

@subheading gnutls_certificate_set_x509_system_trust
@anchor{gnutls_certificate_set_x509_system_trust}
@deftypefun {int} {gnutls_certificate_set_x509_system_trust} (gnutls_certificate_credentials_t       @var{cred})
@var{cred}: is a @code{gnutls_certificate_credentials_t}  type.

This function adds the system's default trusted CAs in order to
verify client or server certificates.

In the case the system is currently unsupported @code{GNUTLS_E_UNIMPLEMENTED_FEATURE} 
is returned.

@strong{Returns:} the number of certificates processed or a negative error code
on error.

@strong{Since:} 3.0.20
@end deftypefun

@subheading gnutls_certificate_set_x509_trust
@anchor{gnutls_certificate_set_x509_trust}
@deftypefun {int} {gnutls_certificate_set_x509_trust} (gnutls_certificate_credentials_t @var{res}, gnutls_x509_crt_t * @var{ca_list}, int @var{ca_list_size})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{ca_list}: is a list of trusted CAs

@var{ca_list_size}: holds the size of the CA list

This function adds the trusted CAs in order to verify client
or server certificates. In case of a client this is not required
to be called if the certificates are not verified using
@code{gnutls_certificate_verify_peers2()} .
This function may be called multiple times.

In case of a server the CAs set here will be sent to the client if
a certificate request is sent. This can be disabled using
@code{gnutls_certificate_send_x509_rdn_sequence()} .

@strong{Returns:} the number of certificates processed or a negative error code
on error.

@strong{Since:} 2.4.0
@end deftypefun

@subheading gnutls_certificate_set_x509_trust_dir
@anchor{gnutls_certificate_set_x509_trust_dir}
@deftypefun {int} {gnutls_certificate_set_x509_trust_dir} (gnutls_certificate_credentials_t @var{cred}, const char * @var{ca_dir}, gnutls_x509_crt_fmt_t @var{type})
@var{cred}: is a @code{gnutls_certificate_credentials_t}  type.

@var{ca_dir}: is a directory containing the list of trusted CAs (DER or PEM list)

@var{type}: is PEM or DER

This function adds the trusted CAs present in the directory in order to
verify client or server certificates. This function is identical
to @code{gnutls_certificate_set_x509_trust_file()}  but loads all certificates
in a directory.

@strong{Returns:} the number of certificates processed

@strong{Since:} 3.3.6
@end deftypefun

@subheading gnutls_certificate_set_x509_trust_file
@anchor{gnutls_certificate_set_x509_trust_file}
@deftypefun {int} {gnutls_certificate_set_x509_trust_file} (gnutls_certificate_credentials_t            @var{cred}, const char * @var{cafile}, gnutls_x509_crt_fmt_t @var{type})
@var{cred}: is a @code{gnutls_certificate_credentials_t}  type.

@var{cafile}: is a file containing the list of trusted CAs (DER or PEM list)

@var{type}: is PEM or DER

This function adds the trusted CAs in order to verify client or
server certificates. In case of a client this is not required to
be called if the certificates are not verified using
@code{gnutls_certificate_verify_peers2()} .  This function may be called
multiple times.

In case of a server the names of the CAs set here will be sent to
the client if a certificate request is sent. This can be disabled
using @code{gnutls_certificate_send_x509_rdn_sequence()} .

This function can also accept URLs. In that case it
will import all certificates that are marked as trusted. Note
that the supported URLs are the ones indicated by @code{gnutls_url_is_supported()} .

@strong{Returns:} the number of certificates processed
@end deftypefun

@subheading gnutls_certificate_set_x509_trust_mem
@anchor{gnutls_certificate_set_x509_trust_mem}
@deftypefun {int} {gnutls_certificate_set_x509_trust_mem} (gnutls_certificate_credentials_t @var{res}, const gnutls_datum_t * @var{ca}, gnutls_x509_crt_fmt_t @var{type})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{ca}: is a list of trusted CAs or a DER certificate

@var{type}: is DER or PEM

This function adds the trusted CAs in order to verify client or
server certificates. In case of a client this is not required to be
called if the certificates are not verified using
@code{gnutls_certificate_verify_peers2()} .  This function may be called
multiple times.

In case of a server the CAs set here will be sent to the client if
a certificate request is sent. This can be disabled using
@code{gnutls_certificate_send_x509_rdn_sequence()} .

@strong{Returns:} the number of certificates processed or a negative error code
on error.
@end deftypefun

@subheading gnutls_certificate_type_get
@anchor{gnutls_certificate_type_get}
@deftypefun {gnutls_certificate_type_t} {gnutls_certificate_type_get} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function returns the type of the certificate that is negotiated
for this side to send to the peer. The certificate type is by default
X.509, unless an alternative certificate type is enabled by
@code{gnutls_init()}  and negotiated during the session.

Resumed sessions will return the certificate type that was negotiated
and used in the original session.

As of version 3.6.4 it is recommended to use
@code{gnutls_certificate_type_get2()}  which is more fine-grained.

@strong{Returns:} the currently used @code{gnutls_certificate_type_t}  certificate
type as negotiated for 'our' side of the connection.
@end deftypefun

@subheading gnutls_certificate_type_get2
@anchor{gnutls_certificate_type_get2}
@deftypefun {gnutls_certificate_type_t} {gnutls_certificate_type_get2} (gnutls_session_t @var{session}, gnutls_ctype_target_t @var{target})
@var{session}: is a @code{gnutls_session_t}  type.

@var{target}: is a @code{gnutls_ctype_target_t}  type.

This function returns the type of the certificate that a side
is negotiated to use.  The certificate type is by default X.509,
unless an alternative certificate type is enabled by @code{gnutls_init()}  and
negotiated during the session.

The  @code{target} parameter specifies whether to request the negotiated
certificate type for the client (@code{GNUTLS_CTYPE_CLIENT} ),
or for the server (@code{GNUTLS_CTYPE_SERVER} ). Additionally, in P2P mode
connection set up where you don't know in advance who will be client
and who will be server you can use the flag (@code{GNUTLS_CTYPE_OURS} ) and
(@code{GNUTLS_CTYPE_PEERS} ) to retrieve the corresponding certificate types.

Resumed sessions will return the certificate type that was negotiated
and used in the original session. That is, this function can be used
to reliably determine the type of the certificate returned by
@code{gnutls_certificate_get_peers()} .

@strong{Returns:} the currently used @code{gnutls_certificate_type_t}  certificate
type for the client or the server.

@strong{Since:} 3.6.4
@end deftypefun

@subheading gnutls_certificate_type_get_id
@anchor{gnutls_certificate_type_get_id}
@deftypefun {gnutls_certificate_type_t} {gnutls_certificate_type_get_id} (const char * @var{name})
@var{name}: is a certificate type name

The names are compared in a case insensitive way.

@strong{Returns:} a @code{gnutls_certificate_type_t}  for the specified in a
string certificate type, or @code{GNUTLS_CRT_UNKNOWN}  on error.
@end deftypefun

@subheading gnutls_certificate_type_get_name
@anchor{gnutls_certificate_type_get_name}
@deftypefun {const char *} {gnutls_certificate_type_get_name} (gnutls_certificate_type_t           @var{type})
@var{type}: is a certificate type

Convert a @code{gnutls_certificate_type_t}  type to a string.

@strong{Returns:} a string that contains the name of the specified
certificate type, or @code{NULL}  in case of unknown types.
@end deftypefun

@subheading gnutls_certificate_type_list
@anchor{gnutls_certificate_type_list}
@deftypefun {const gnutls_certificate_type_t *} {gnutls_certificate_type_list} ( @var{void})

Get a list of certificate types.

@strong{Returns:} a (0)-terminated list of @code{gnutls_certificate_type_t} 
integers indicating the available certificate types.
@end deftypefun

@subheading gnutls_certificate_verification_status_print
@anchor{gnutls_certificate_verification_status_print}
@deftypefun {int} {gnutls_certificate_verification_status_print} (unsigned int @var{status}, gnutls_certificate_type_t           @var{type}, gnutls_datum_t * @var{out}, unsigned int @var{flags})
@var{status}: The status flags to be printed

@var{type}: The certificate type

@var{out}: Newly allocated datum with (0) terminated string.

@var{flags}: should be zero

This function will pretty print the status of a verification
process -- eg. the one obtained by @code{gnutls_certificate_verify_peers3()} .

The output  @code{out} needs to be deallocated using @code{gnutls_free()} .

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a
negative error value.

@strong{Since:} 3.1.4
@end deftypefun

@subheading gnutls_certificate_verify_peers
@anchor{gnutls_certificate_verify_peers}
@deftypefun {int} {gnutls_certificate_verify_peers} (gnutls_session_t @var{session}, gnutls_typed_vdata_st * @var{data}, unsigned int @var{elements}, unsigned int * @var{status})
@var{session}: is a gnutls session

@var{data}: an array of typed data

@var{elements}: the number of data elements

@var{status}: is the output of the verification

This function will verify the peer's certificate and store the
the status in the  @code{status} variable as a bitwise OR of gnutls_certificate_status_t
values or zero if the certificate is trusted. Note that value in  @code{status} is set only when the return value of this function is success (i.e, failure 
to trust a certificate does not imply a negative return value).
The default verification flags used by this function can be overridden
using @code{gnutls_certificate_set_verify_flags()} . See the documentation
of @code{gnutls_certificate_verify_peers2()}  for details in the verification process.

This function will take into account the stapled OCSP responses sent by the server,
as well as the following X.509 certificate extensions: Name Constraints,
Key Usage, and Basic Constraints (pathlen).

The acceptable  @code{data} types are @code{GNUTLS_DT_DNS_HOSTNAME} , @code{GNUTLS_DT_RFC822NAME}  and @code{GNUTLS_DT_KEY_PURPOSE_OID} .
The former two accept as data a null-terminated hostname or email address, and the latter a null-terminated
object identifier (e.g., @code{GNUTLS_KP_TLS_WWW_SERVER} ).

If a DNS hostname is provided then this function will compare
the hostname in the certificate against the given. If names do not match the 
@code{GNUTLS_CERT_UNEXPECTED_OWNER}  status flag will be set.
If a key purpose OID is provided and the end-certificate contains the extended key
usage PKIX extension, it will be required to be have the provided key purpose 
or be marked for any purpose, otherwise verification status will have the
@code{GNUTLS_CERT_SIGNER_CONSTRAINTS_FAILURE}  flag set.

To avoid denial of service attacks some
default upper limits regarding the certificate key size and chain
size are set. To override them use @code{gnutls_certificate_set_verify_limits()} .

Note that when using raw public-keys verification will not work because there is
no corresponding certificate body belonging to the raw key that can be verified. In that
case this function will return @code{GNUTLS_E_INVALID_REQUEST} .

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  (0) when the validation is performed, or a negative error code otherwise.
A successful error code means that the  @code{status} parameter must be checked to obtain the validation status.

@strong{Since:} 3.3.0
@end deftypefun

@subheading gnutls_certificate_verify_peers2
@anchor{gnutls_certificate_verify_peers2}
@deftypefun {int} {gnutls_certificate_verify_peers2} (gnutls_session_t @var{session}, unsigned int * @var{status})
@var{session}: is a gnutls session

@var{status}: is the output of the verification

This function will verify the peer's certificate and store
the status in the  @code{status} variable as a bitwise OR of gnutls_certificate_status_t
values or zero if the certificate is trusted. Note that value in  @code{status} is set only when the return value of this function is success (i.e, failure 
to trust a certificate does not imply a negative return value).
The default verification flags used by this function can be overridden
using @code{gnutls_certificate_set_verify_flags()} .

This function will take into account the stapled OCSP responses sent by the server,
as well as the following X.509 certificate extensions: Name Constraints,
Key Usage, and Basic Constraints (pathlen).

Note that you must also check the peer's name in order to check if
the verified certificate belongs to the actual peer, see @code{gnutls_x509_crt_check_hostname()} ,
or use @code{gnutls_certificate_verify_peers3()} .

To avoid denial of service attacks some
default upper limits regarding the certificate key size and chain
size are set. To override them use @code{gnutls_certificate_set_verify_limits()} .

Note that when using raw public-keys verification will not work because there is
no corresponding certificate body belonging to the raw key that can be verified. In that
case this function will return @code{GNUTLS_E_INVALID_REQUEST} .

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  (0) when the validation is performed, or a negative error code otherwise.
A successful error code means that the  @code{status} parameter must be checked to obtain the validation status.
@end deftypefun

@subheading gnutls_certificate_verify_peers3
@anchor{gnutls_certificate_verify_peers3}
@deftypefun {int} {gnutls_certificate_verify_peers3} (gnutls_session_t @var{session}, const char * @var{hostname}, unsigned int * @var{status})
@var{session}: is a gnutls session

@var{hostname}: is the expected name of the peer; may be @code{NULL} 

@var{status}: is the output of the verification

This function will verify the peer's certificate and store the
the status in the  @code{status} variable as a bitwise OR of gnutls_certificate_status_t
values or zero if the certificate is trusted. Note that value in  @code{status} is set only when the return value of this function is success (i.e, failure 
to trust a certificate does not imply a negative return value).
The default verification flags used by this function can be overridden
using @code{gnutls_certificate_set_verify_flags()} . See the documentation
of @code{gnutls_certificate_verify_peers2()}  for details in the verification process.

This function will take into account the stapled OCSP responses sent by the server,
as well as the following X.509 certificate extensions: Name Constraints,
Key Usage, and Basic Constraints (pathlen).

If the  @code{hostname} provided is non-NULL then this function will compare
the hostname in the certificate against it. The comparison will follow
the RFC6125 recommendations. If names do not match the
@code{GNUTLS_CERT_UNEXPECTED_OWNER}  status flag will be set.

In order to verify the purpose of the end-certificate (by checking the extended
key usage), use @code{gnutls_certificate_verify_peers()} .

To avoid denial of service attacks some
default upper limits regarding the certificate key size and chain
size are set. To override them use @code{gnutls_certificate_set_verify_limits()} .

Note that when using raw public-keys verification will not work because there is
no corresponding certificate body belonging to the raw key that can be verified. In that
case this function will return @code{GNUTLS_E_INVALID_REQUEST} .

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  (0) when the validation is performed, or a negative error code otherwise.
A successful error code means that the  @code{status} parameter must be checked to obtain the validation status.

@strong{Since:} 3.1.4
@end deftypefun

@subheading gnutls_check_version
@anchor{gnutls_check_version}
@deftypefun {const char *} {gnutls_check_version} (const char * @var{req_version})
@var{req_version}: version string to compare with, or @code{NULL} .

Check the GnuTLS Library version against the provided string.
See @code{GNUTLS_VERSION}  for a suitable  @code{req_version} string.

See also @code{gnutls_check_version_numeric()} , which provides this
functionality as a macro.

@strong{Returns:} Check that the version of the library is at
minimum the one given as a string in  @code{req_version} and return the
actual version string of the library; return @code{NULL}  if the
condition is not met.  If @code{NULL}  is passed to this function no
check is done and only the version string is returned.
@end deftypefun

@subheading gnutls_cipher_get
@anchor{gnutls_cipher_get}
@deftypefun {gnutls_cipher_algorithm_t} {gnutls_cipher_get} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get the currently used cipher.

@strong{Returns:} the currently used cipher, a @code{gnutls_cipher_algorithm_t} 
type.
@end deftypefun

@subheading gnutls_cipher_get_id
@anchor{gnutls_cipher_get_id}
@deftypefun {gnutls_cipher_algorithm_t} {gnutls_cipher_get_id} (const char * @var{name})
@var{name}: is a cipher algorithm name

The names are compared in a case insensitive way.

@strong{Returns:} return a @code{gnutls_cipher_algorithm_t}  value corresponding to
the specified cipher, or @code{GNUTLS_CIPHER_UNKNOWN}  on error.
@end deftypefun

@subheading gnutls_cipher_get_key_size
@anchor{gnutls_cipher_get_key_size}
@deftypefun {size_t} {gnutls_cipher_get_key_size} (gnutls_cipher_algorithm_t @var{algorithm})
@var{algorithm}: is an encryption algorithm

This function returns the key size of the provided algorithm.

@strong{Returns:} length (in bytes) of the given cipher's key size, or 0 if
the given cipher is invalid.
@end deftypefun

@subheading gnutls_cipher_get_name
@anchor{gnutls_cipher_get_name}
@deftypefun {const char *} {gnutls_cipher_get_name} (gnutls_cipher_algorithm_t @var{algorithm})
@var{algorithm}: is an encryption algorithm

Convert a @code{gnutls_cipher_algorithm_t}  type to a string.

@strong{Returns:} a pointer to a string that contains the name of the
specified cipher, or @code{NULL} .
@end deftypefun

@subheading gnutls_cipher_list
@anchor{gnutls_cipher_list}
@deftypefun {const gnutls_cipher_algorithm_t *} {gnutls_cipher_list} ( @var{void})

Get a list of supported cipher algorithms.  Note that not
necessarily all ciphers are supported as TLS cipher suites.  For
example, DES is not supported as a cipher suite, but is supported
for other purposes (e.g., PKCS@code{8}  or similar).

This function is not thread safe.

@strong{Returns:} a (0)-terminated list of @code{gnutls_cipher_algorithm_t} 
integers indicating the available ciphers.
@end deftypefun

@subheading gnutls_cipher_suite_get_name
@anchor{gnutls_cipher_suite_get_name}
@deftypefun {const char *} {gnutls_cipher_suite_get_name} (gnutls_kx_algorithm_t       @var{kx_algorithm}, gnutls_cipher_algorithm_t       @var{cipher_algorithm}, gnutls_mac_algorithm_t       @var{mac_algorithm})
@var{kx_algorithm}: is a Key exchange algorithm

@var{cipher_algorithm}: is a cipher algorithm

@var{mac_algorithm}: is a MAC algorithm

This function returns the ciphersuite name under TLS1.2 or earlier
versions when provided with individual algorithms. The full cipher suite
name must be prepended by TLS or SSL depending of the protocol in use.

To get a description of the current ciphersuite across versions, it
is recommended to use @code{gnutls_session_get_desc()} .

@strong{Returns:} a string that contains the name of a TLS cipher suite,
specified by the given algorithms, or @code{NULL} .
@end deftypefun

@subheading gnutls_cipher_suite_info
@anchor{gnutls_cipher_suite_info}
@deftypefun {const char *} {gnutls_cipher_suite_info} (size_t @var{idx}, unsigned char * @var{cs_id}, gnutls_kx_algorithm_t * @var{kx}, gnutls_cipher_algorithm_t * @var{cipher}, gnutls_mac_algorithm_t * @var{mac}, gnutls_protocol_t * @var{min_version})
@var{idx}: index of cipher suite to get information about, starts on 0.

@var{cs_id}: output buffer with room for 2 bytes, indicating cipher suite value

@var{kx}: output variable indicating key exchange algorithm, or @code{NULL} .

@var{cipher}: output variable indicating cipher, or @code{NULL} .

@var{mac}: output variable indicating MAC algorithm, or @code{NULL} .

@var{min_version}: output variable indicating TLS protocol version, or @code{NULL} .

Get information about supported cipher suites.  Use the function
iteratively to get information about all supported cipher suites.
Call with idx=0 to get information about first cipher suite, then
idx=1 and so on until the function returns NULL.

@strong{Returns:} the name of  @code{idx} cipher suite, and set the information
about the cipher suite in the output variables.  If  @code{idx} is out of
bounds, @code{NULL}  is returned.
@end deftypefun

@subheading gnutls_ciphersuite_get
@anchor{gnutls_ciphersuite_get}
@deftypefun {const char *} {gnutls_ciphersuite_get} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get the canonical name of negotiated TLS ciphersuite.  The names
returned by this function match the IANA registry, with one
exception:

TLS_DHE_DSS_RC4_128_SHA @{ 0x00, 0x66 @}

which is reserved for compatibility.

To get a detailed description of the current ciphersuite, it is
recommended to use @code{gnutls_session_get_desc()} .

@strong{Returns:} a string that contains the canonical name of a TLS ciphersuite,
or @code{NULL}  if the handshake is not completed.

@strong{Since:} 3.7.4
@end deftypefun

@subheading gnutls_compress_certificate_get_selected_method
@anchor{gnutls_compress_certificate_get_selected_method}
@deftypefun {gnutls_compression_method_t} {gnutls_compress_certificate_get_selected_method} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function returns the certificate compression method that has been
selected to compress the certificate before sending it to the peer.
The selection is done based on the local list of supported compression
methods and the peer's requested compression methods.

@strong{Returns:} selected certificate compression method.

Since 3.7.4
@end deftypefun

@subheading gnutls_compress_certificate_set_methods
@anchor{gnutls_compress_certificate_set_methods}
@deftypefun {int} {gnutls_compress_certificate_set_methods} (gnutls_session_t @var{session}, const gnutls_compression_method_t * @var{methods}, size_t @var{methods_len})
@var{session}: is a @code{gnutls_session_t}  type.

@var{methods}: is a list of supported compression methods.

@var{methods_len}: number of compression methods in  @code{methods} 

This function sets the supported compression methods for certificate compression
for the given session. The list of supported compression methods will be used
for a) requesting the compression of peer's certificate and b) selecting the
method to compress the local certificate before sending it to the peer.
The order of compression methods inside the list does matter as the method
that appears earlier in the list will be preffered before the later ones.
Note that even if you set the list of supported compression methods, the
compression might not be used if the peer does not support any of your chosen
compression methods.

The list of supported compression methods must meet the following criteria:
Argument  @code{methods} must be an array of valid compression methods of type
@code{gnutls_compression_method_t} . Argument  @code{methods_len} must contain the number of
compression methods stored in the  @code{methods} array and must be within range <1, 127>.
The length constraints are defined by @code{MIN_COMPRESS_CERTIFICATE_METHODS} 
and @code{MAX_COMPRESS_CERTIFICATE_METHODS}  macros located in the header file
compress_certificate.h.

If either  @code{methods} or  @code{methods_len} is equal to 0, current list of supported
compression methods will be unset.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

Since 3.7.4
@end deftypefun

@subheading gnutls_credentials_clear
@anchor{gnutls_credentials_clear}
@deftypefun {void} {gnutls_credentials_clear} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Clears all the credentials previously set in this session.
@end deftypefun

@subheading gnutls_credentials_get
@anchor{gnutls_credentials_get}
@deftypefun {int} {gnutls_credentials_get} (gnutls_session_t @var{session}, gnutls_credentials_type_t @var{type}, void ** @var{cred})
@var{session}: is a @code{gnutls_session_t}  type.

@var{type}: is the type of the credentials to return

@var{cred}: will contain the credentials.

Returns the previously provided credentials structures.

For @code{GNUTLS_CRD_ANON} ,  @code{cred} will be
@code{gnutls_anon_client_credentials_t}  in case of a client.  In case of
a server it should be @code{gnutls_anon_server_credentials_t} .

For @code{GNUTLS_CRD_SRP} ,  @code{cred} will be @code{gnutls_srp_client_credentials_t} 
in case of a client, and @code{gnutls_srp_server_credentials_t} , in case
of a server.

For @code{GNUTLS_CRD_CERTIFICATE} ,  @code{cred} will be
@code{gnutls_certificate_credentials_t} .

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

@strong{Since:} 3.3.3
@end deftypefun

@subheading gnutls_credentials_set
@anchor{gnutls_credentials_set}
@deftypefun {int} {gnutls_credentials_set} (gnutls_session_t @var{session}, gnutls_credentials_type_t @var{type}, void * @var{cred})
@var{session}: is a @code{gnutls_session_t}  type.

@var{type}: is the type of the credentials

@var{cred}: the credentials to set

Sets the needed credentials for the specified type.  E.g. username,
password - or public and private keys etc.  The  @code{cred} parameter is
a structure that depends on the specified type and on the current
session (client or server).

In order to minimize memory usage, and share credentials between
several threads gnutls keeps a pointer to cred, and not the whole
cred structure.  Thus you will have to keep the structure allocated
until you call @code{gnutls_deinit()} .

For @code{GNUTLS_CRD_ANON} ,  @code{cred} should be
@code{gnutls_anon_client_credentials_t}  in case of a client.  In case of
a server it should be @code{gnutls_anon_server_credentials_t} .

For @code{GNUTLS_CRD_SRP} ,  @code{cred} should be @code{gnutls_srp_client_credentials_t} 
in case of a client, and @code{gnutls_srp_server_credentials_t} , in case
of a server.

For @code{GNUTLS_CRD_CERTIFICATE} ,  @code{cred} should be
@code{gnutls_certificate_credentials_t} .

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_db_check_entry
@anchor{gnutls_db_check_entry}
@deftypefun {int} {gnutls_db_check_entry} (gnutls_session_t @var{session}, gnutls_datum_t @var{session_entry})
@var{session}: is a @code{gnutls_session_t}  type.

@var{session_entry}: is the session data (not key)

This function has no effect. 

@strong{Returns:} Returns @code{GNUTLS_E_EXPIRED} , if the database entry has
expired or 0 otherwise.

@strong{Deprecated:} This function is deprecated.
@end deftypefun

@subheading gnutls_db_check_entry_expire_time
@anchor{gnutls_db_check_entry_expire_time}
@deftypefun {time_t} {gnutls_db_check_entry_expire_time} (gnutls_datum_t * @var{entry})
@var{entry}: is a pointer to a @code{gnutls_datum_t}  type.

This function returns the time that this entry will expire.
It can be used for database entry expiration.

@strong{Returns:} The time this entry will expire, or zero on error.

@strong{Since:} 3.6.5
@end deftypefun

@subheading gnutls_db_check_entry_time
@anchor{gnutls_db_check_entry_time}
@deftypefun {time_t} {gnutls_db_check_entry_time} (gnutls_datum_t * @var{entry})
@var{entry}: is a pointer to a @code{gnutls_datum_t}  type.

This function returns the time that this entry was active.
It can be used for database entry expiration.

@strong{Returns:} The time this entry was created, or zero on error.
@end deftypefun

@subheading gnutls_db_get_default_cache_expiration
@anchor{gnutls_db_get_default_cache_expiration}
@deftypefun {unsigned} {gnutls_db_get_default_cache_expiration} ( @var{void})

Returns the expiration time (in seconds) of stored sessions for resumption. 
@end deftypefun

@subheading gnutls_db_get_ptr
@anchor{gnutls_db_get_ptr}
@deftypefun {void *} {gnutls_db_get_ptr} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get db function pointer.

@strong{Returns:} the pointer that will be sent to db store, retrieve and
delete functions, as the first argument.
@end deftypefun

@subheading gnutls_db_remove_session
@anchor{gnutls_db_remove_session}
@deftypefun {void} {gnutls_db_remove_session} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function will remove the current session data from the
session database.  This will prevent future handshakes reusing
these session data.  This function should be called if a session
was terminated abnormally, and before @code{gnutls_deinit()}  is called.

Normally @code{gnutls_deinit()}  will remove abnormally terminated
sessions.
@end deftypefun

@subheading gnutls_db_set_cache_expiration
@anchor{gnutls_db_set_cache_expiration}
@deftypefun {void} {gnutls_db_set_cache_expiration} (gnutls_session_t @var{session}, int @var{seconds})
@var{session}: is a @code{gnutls_session_t}  type.

@var{seconds}: is the number of seconds.

Set the expiration time for resumed sessions. The default is 21600
(6 hours) at the time of writing.

The maximum value that can be set using this function is 604800
(7 days).
@end deftypefun

@subheading gnutls_db_set_ptr
@anchor{gnutls_db_set_ptr}
@deftypefun {void} {gnutls_db_set_ptr} (gnutls_session_t @var{session}, void * @var{ptr})
@var{session}: is a @code{gnutls_session_t}  type.

@var{ptr}: is the pointer

Sets the pointer that will be provided to db store, retrieve and
delete functions, as the first argument.
@end deftypefun

@subheading gnutls_db_set_remove_function
@anchor{gnutls_db_set_remove_function}
@deftypefun {void} {gnutls_db_set_remove_function} (gnutls_session_t @var{session}, gnutls_db_remove_func @var{rem_func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{rem_func}: is the function.

Sets the function that will be used to remove data from the
resumed sessions database. This function must return 0 on success.

The first argument to  @code{rem_func} will be null unless
@code{gnutls_db_set_ptr()}  has been called.
@end deftypefun

@subheading gnutls_db_set_retrieve_function
@anchor{gnutls_db_set_retrieve_function}
@deftypefun {void} {gnutls_db_set_retrieve_function} (gnutls_session_t @var{session}, gnutls_db_retr_func @var{retr_func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{retr_func}: is the function.

Sets the function that will be used to retrieve data from the
resumed sessions database.  This function must return a
gnutls_datum_t containing the data on success, or a gnutls_datum_t
containing null and 0 on failure.

The datum's data must be allocated using the function
@code{gnutls_malloc()} .

The first argument to  @code{retr_func} will be null unless
@code{gnutls_db_set_ptr()}  has been called.
@end deftypefun

@subheading gnutls_db_set_store_function
@anchor{gnutls_db_set_store_function}
@deftypefun {void} {gnutls_db_set_store_function} (gnutls_session_t @var{session}, gnutls_db_store_func @var{store_func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{store_func}: is the function

Sets the function that will be used to store data in the resumed
sessions database. This function must return 0 on success.

The first argument to  @code{store_func} will be null unless
@code{gnutls_db_set_ptr()}  has been called.
@end deftypefun

@subheading gnutls_deinit
@anchor{gnutls_deinit}
@deftypefun {void} {gnutls_deinit} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function clears all buffers associated with the  @code{session} .
This function will also remove session data from the session
database if the session was terminated abnormally.
@end deftypefun

@subheading gnutls_dh_get_group
@anchor{gnutls_dh_get_group}
@deftypefun {int} {gnutls_dh_get_group} (gnutls_session_t @var{session}, gnutls_datum_t * @var{raw_gen}, gnutls_datum_t * @var{raw_prime})
@var{session}: is a gnutls session

@var{raw_gen}: will hold the generator.

@var{raw_prime}: will hold the prime.

This function will return the group parameters used in the last
Diffie-Hellman key exchange with the peer.  These are the prime and
the generator used.  This function should be used for both
anonymous and ephemeral Diffie-Hellman.  The output parameters must
be freed with @code{gnutls_free()} .

Note, that the prime and generator are exported as non-negative
integers and may include a leading zero byte.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_dh_get_peers_public_bits
@anchor{gnutls_dh_get_peers_public_bits}
@deftypefun {int} {gnutls_dh_get_peers_public_bits} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

Get the Diffie-Hellman public key bit size.  Can be used for both
anonymous and ephemeral Diffie-Hellman.

@strong{Returns:} The public key bit size used in the last Diffie-Hellman
key exchange with the peer, or a negative error code in case of error.
@end deftypefun

@subheading gnutls_dh_get_prime_bits
@anchor{gnutls_dh_get_prime_bits}
@deftypefun {int} {gnutls_dh_get_prime_bits} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

This function will return the bits of the prime used in the last
Diffie-Hellman key exchange with the peer.  Should be used for both
anonymous and ephemeral Diffie-Hellman.  Note that some ciphers,
like RSA and DSA without DHE, do not use a Diffie-Hellman key
exchange, and then this function will return 0.

@strong{Returns:} The Diffie-Hellman bit strength is returned, or 0 if no
Diffie-Hellman key exchange was done, or a negative error code on
failure.
@end deftypefun

@subheading gnutls_dh_get_pubkey
@anchor{gnutls_dh_get_pubkey}
@deftypefun {int} {gnutls_dh_get_pubkey} (gnutls_session_t @var{session}, gnutls_datum_t * @var{raw_key})
@var{session}: is a gnutls session

@var{raw_key}: will hold the public key.

This function will return the peer's public key used in the last
Diffie-Hellman key exchange.  This function should be used for both
anonymous and ephemeral Diffie-Hellman.  The output parameters must
be freed with @code{gnutls_free()} .

Note, that public key is exported as non-negative
integer and may include a leading zero byte.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_dh_get_secret_bits
@anchor{gnutls_dh_get_secret_bits}
@deftypefun {int} {gnutls_dh_get_secret_bits} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

This function will return the bits used in the last Diffie-Hellman
key exchange with the peer.  Should be used for both anonymous and
ephemeral Diffie-Hellman.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_dh_params_cpy
@anchor{gnutls_dh_params_cpy}
@deftypefun {int} {gnutls_dh_params_cpy} (gnutls_dh_params_t @var{dst}, gnutls_dh_params_t @var{src})
@var{dst}: Is the destination parameters, which should be initialized.

@var{src}: Is the source parameters

This function will copy the DH parameters structure from source
to destination. The destination should be already initialized.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_dh_params_deinit
@anchor{gnutls_dh_params_deinit}
@deftypefun {void} {gnutls_dh_params_deinit} (gnutls_dh_params_t @var{dh_params})
@var{dh_params}: The parameters

This function will deinitialize the DH parameters type.
@end deftypefun

@subheading gnutls_dh_params_export2_pkcs3
@anchor{gnutls_dh_params_export2_pkcs3}
@deftypefun {int} {gnutls_dh_params_export2_pkcs3} (gnutls_dh_params_t @var{params}, gnutls_x509_crt_fmt_t @var{format}, gnutls_datum_t * @var{out})
@var{params}: Holds the DH parameters

@var{format}: the format of output params. One of PEM or DER.

@var{out}: will contain a PKCS3 DHParams structure PEM or DER encoded

This function will export the given dh parameters to a PKCS3
DHParams structure. This is the format generated by "openssl dhparam" tool.
The data in  @code{out} will be allocated using @code{gnutls_malloc()} .

If the structure is PEM encoded, it will have a header
of "BEGIN DH PARAMETERS".

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

@strong{Since:} 3.1.3
@end deftypefun

@subheading gnutls_dh_params_export_pkcs3
@anchor{gnutls_dh_params_export_pkcs3}
@deftypefun {int} {gnutls_dh_params_export_pkcs3} (gnutls_dh_params_t @var{params}, gnutls_x509_crt_fmt_t @var{format}, unsigned char * @var{params_data}, size_t * @var{params_data_size})
@var{params}: Holds the DH parameters

@var{format}: the format of output params. One of PEM or DER.

@var{params_data}: will contain a PKCS3 DHParams structure PEM or DER encoded

@var{params_data_size}: holds the size of params_data (and will be replaced by the actual size of parameters)

This function will export the given dh parameters to a PKCS3
DHParams structure. This is the format generated by "openssl dhparam" tool.
If the buffer provided is not long enough to hold the output, then
GNUTLS_E_SHORT_MEMORY_BUFFER will be returned.

If the structure is PEM encoded, it will have a header
of "BEGIN DH PARAMETERS".

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_dh_params_export_raw
@anchor{gnutls_dh_params_export_raw}
@deftypefun {int} {gnutls_dh_params_export_raw} (gnutls_dh_params_t @var{params}, gnutls_datum_t * @var{prime}, gnutls_datum_t * @var{generator}, unsigned int * @var{bits})
@var{params}: Holds the DH parameters

@var{prime}: will hold the new prime

@var{generator}: will hold the new generator

@var{bits}: if non null will hold the secret key's number of bits

This function will export the pair of prime and generator for use
in the Diffie-Hellman key exchange.  The new parameters will be
allocated using @code{gnutls_malloc()}  and will be stored in the
appropriate datum.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_dh_params_generate2
@anchor{gnutls_dh_params_generate2}
@deftypefun {int} {gnutls_dh_params_generate2} (gnutls_dh_params_t @var{dparams}, unsigned int @var{bits})
@var{dparams}: The parameters

@var{bits}: is the prime's number of bits

This function will generate a new pair of prime and generator for use in
the Diffie-Hellman key exchange. This may take long time.

It is recommended not to set the number of bits directly, but 
use @code{gnutls_sec_param_to_pk_bits()}  instead.
Also note that the DH parameters are only useful to servers.
Since clients use the parameters sent by the server, it's of
no use to call this in client side.

The parameters generated are of the DSA form. It also is possible
to generate provable parameters (following the Shawe-Taylor
algorithm), using @code{gnutls_x509_privkey_generate2()}  with DSA option
and the @code{GNUTLS_PRIVKEY_FLAG_PROVABLE}  flag set. These can the
be imported with @code{gnutls_dh_params_import_dsa()} .

It is no longer recommended for applications to generate parameters.
See the "Parameter generation" section in the manual.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_dh_params_import_dsa
@anchor{gnutls_dh_params_import_dsa}
@deftypefun {int} {gnutls_dh_params_import_dsa} (gnutls_dh_params_t @var{dh_params}, gnutls_x509_privkey_t @var{key})
@var{dh_params}: The parameters

@var{key}: holds a DSA private key

This function will import the prime and generator of the DSA key for use 
in the Diffie-Hellman key exchange.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_dh_params_import_pkcs3
@anchor{gnutls_dh_params_import_pkcs3}
@deftypefun {int} {gnutls_dh_params_import_pkcs3} (gnutls_dh_params_t @var{params}, const gnutls_datum_t * @var{pkcs3_params}, gnutls_x509_crt_fmt_t @var{format})
@var{params}: The parameters

@var{pkcs3_params}: should contain a PKCS3 DHParams structure PEM or DER encoded

@var{format}: the format of params. PEM or DER.

This function will extract the DHParams found in a PKCS3 formatted
structure. This is the format generated by "openssl dhparam" tool.

If the structure is PEM encoded, it should have a header
of "BEGIN DH PARAMETERS".

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_dh_params_import_raw
@anchor{gnutls_dh_params_import_raw}
@deftypefun {int} {gnutls_dh_params_import_raw} (gnutls_dh_params_t @var{dh_params}, const gnutls_datum_t * @var{prime}, const gnutls_datum_t * @var{generator})
@var{dh_params}: The parameters

@var{prime}: holds the new prime

@var{generator}: holds the new generator

This function will replace the pair of prime and generator for use
in the Diffie-Hellman key exchange.  The new parameters should be
stored in the appropriate gnutls_datum.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_dh_params_import_raw2
@anchor{gnutls_dh_params_import_raw2}
@deftypefun {int} {gnutls_dh_params_import_raw2} (gnutls_dh_params_t @var{dh_params}, const gnutls_datum_t * @var{prime}, const gnutls_datum_t * @var{generator}, unsigned @var{key_bits})
@var{dh_params}: The parameters

@var{prime}: holds the new prime

@var{generator}: holds the new generator

@var{key_bits}: the private key bits (set to zero when unknown)

This function will replace the pair of prime and generator for use
in the Diffie-Hellman key exchange.  The new parameters should be
stored in the appropriate gnutls_datum.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_dh_params_import_raw3
@anchor{gnutls_dh_params_import_raw3}
@deftypefun {int} {gnutls_dh_params_import_raw3} (gnutls_dh_params_t @var{dh_params}, const gnutls_datum_t * @var{prime}, const gnutls_datum_t * @var{q}, const gnutls_datum_t * @var{generator})
@var{dh_params}: The parameters

@var{prime}: holds the new prime

@var{q}: holds the subgroup if available, otherwise NULL

@var{generator}: holds the new generator

This function will replace the pair of prime and generator for use
in the Diffie-Hellman key exchange.  The new parameters should be
stored in the appropriate gnutls_datum.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_dh_params_init
@anchor{gnutls_dh_params_init}
@deftypefun {int} {gnutls_dh_params_init} (gnutls_dh_params_t * @var{dh_params})
@var{dh_params}: The parameters

This function will initialize the DH parameters type.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_dh_set_prime_bits
@anchor{gnutls_dh_set_prime_bits}
@deftypefun {void} {gnutls_dh_set_prime_bits} (gnutls_session_t @var{session}, unsigned int @var{bits})
@var{session}: is a @code{gnutls_session_t}  type.

@var{bits}: is the number of bits

This function sets the number of bits, for use in a Diffie-Hellman
key exchange.  This is used both in DH ephemeral and DH anonymous
cipher suites.  This will set the minimum size of the prime that
will be used for the handshake.

In the client side it sets the minimum accepted number of bits.  If
a server sends a prime with less bits than that
@code{GNUTLS_E_DH_PRIME_UNACCEPTABLE}  will be returned by the handshake.

Note that this function will warn via the audit log for value that
are believed to be weak.

The function has no effect in server side.

Note that since 3.1.7 this function is deprecated. The minimum
number of bits is set by the priority string level.
Also this function must be called after @code{gnutls_priority_set_direct()} 
or the set value may be overridden by the selected priority options.
@end deftypefun

@subheading gnutls_digest_get_id
@anchor{gnutls_digest_get_id}
@deftypefun {gnutls_digest_algorithm_t} {gnutls_digest_get_id} (const char * @var{name})
@var{name}: is a digest algorithm name

Convert a string to a @code{gnutls_digest_algorithm_t}  value.  The names are
compared in a case insensitive way.

@strong{Returns:} a @code{gnutls_digest_algorithm_t}  id of the specified MAC
algorithm string, or @code{GNUTLS_DIG_UNKNOWN}  on failure.
@end deftypefun

@subheading gnutls_digest_get_name
@anchor{gnutls_digest_get_name}
@deftypefun {const char *} {gnutls_digest_get_name} (gnutls_digest_algorithm_t @var{algorithm})
@var{algorithm}: is a digest algorithm

Convert a @code{gnutls_digest_algorithm_t}  value to a string.

@strong{Returns:} a string that contains the name of the specified digest
algorithm, or @code{NULL} .
@end deftypefun

@subheading gnutls_digest_get_oid
@anchor{gnutls_digest_get_oid}
@deftypefun {const char *} {gnutls_digest_get_oid} (gnutls_digest_algorithm_t @var{algorithm})
@var{algorithm}: is a digest algorithm

Convert a @code{gnutls_digest_algorithm_t}  value to its object identifier.

@strong{Returns:} a string that contains the object identifier of the specified digest
algorithm, or @code{NULL} .

@strong{Since:} 3.4.3
@end deftypefun

@subheading gnutls_digest_list
@anchor{gnutls_digest_list}
@deftypefun {const gnutls_digest_algorithm_t *} {gnutls_digest_list} ( @var{void})

Get a list of hash (digest) algorithms supported by GnuTLS.

This function is not thread safe.

@strong{Returns:} Return a (0)-terminated list of @code{gnutls_digest_algorithm_t} 
integers indicating the available digests.
@end deftypefun

@subheading gnutls_digest_set_secure
@anchor{gnutls_digest_set_secure}
@deftypefun {int} {gnutls_digest_set_secure} (gnutls_digest_algorithm_t @var{dig}, unsigned int @var{secure})
@var{dig}: is a digest algorithm

@var{secure}: whether to mark the digest algorithm secure

Modify the previous system wide setting that marked  @code{dig} as secure
or insecure. This only has effect when the algorithm is enabled
through the allowlisting mode in the configuration file, or when
the setting is modified with a prior call to this function.

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_early_cipher_get
@anchor{gnutls_early_cipher_get}
@deftypefun {gnutls_cipher_algorithm_t} {gnutls_early_cipher_get} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get the cipher algorithm used for encrypting early data.

@strong{Returns:} the cipher used for early data, a
@code{gnutls_cipher_algorithm_t}  type.

@strong{Since:} 3.7.2
@end deftypefun

@subheading gnutls_early_prf_hash_get
@anchor{gnutls_early_prf_hash_get}
@deftypefun {gnutls_digest_algorithm_t} {gnutls_early_prf_hash_get} (const gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get the hash algorithm used as a PRF to derive keys for encrypting
early data in TLS 1.3.

@strong{Returns:} the hash algorithm used for early data, a
@code{gnutls_digest_algorithm_t}  value.

@strong{Since:} 3.7.2
@end deftypefun

@subheading gnutls_ecc_curve_get
@anchor{gnutls_ecc_curve_get}
@deftypefun {gnutls_ecc_curve_t} {gnutls_ecc_curve_get} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Returns the currently used elliptic curve for key exchange. Only valid
when using an elliptic curve ciphersuite.

@strong{Returns:} the currently used curve, a @code{gnutls_ecc_curve_t} 
type.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_ecc_curve_get_id
@anchor{gnutls_ecc_curve_get_id}
@deftypefun {gnutls_ecc_curve_t} {gnutls_ecc_curve_get_id} (const char * @var{name})
@var{name}: is a curve name

The names are compared in a case insensitive way.

@strong{Returns:} return a @code{gnutls_ecc_curve_t}  value corresponding to
the specified curve, or @code{GNUTLS_ECC_CURVE_INVALID}  on error.

@strong{Since:} 3.4.3
@end deftypefun

@subheading gnutls_ecc_curve_get_name
@anchor{gnutls_ecc_curve_get_name}
@deftypefun {const char *} {gnutls_ecc_curve_get_name} (gnutls_ecc_curve_t @var{curve})
@var{curve}: is an ECC curve

Convert a @code{gnutls_ecc_curve_t}  value to a string.

@strong{Returns:} a string that contains the name of the specified
curve or @code{NULL} .

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_ecc_curve_get_oid
@anchor{gnutls_ecc_curve_get_oid}
@deftypefun {const char *} {gnutls_ecc_curve_get_oid} (gnutls_ecc_curve_t @var{curve})
@var{curve}: is an ECC curve

Convert a @code{gnutls_ecc_curve_t}  value to its object identifier.

@strong{Returns:} a string that contains the OID of the specified
curve or @code{NULL} .

@strong{Since:} 3.4.3
@end deftypefun

@subheading gnutls_ecc_curve_get_pk
@anchor{gnutls_ecc_curve_get_pk}
@deftypefun {gnutls_pk_algorithm_t} {gnutls_ecc_curve_get_pk} (gnutls_ecc_curve_t @var{curve})
@var{curve}: is an ECC curve


@strong{Returns:} the public key algorithm associated with the named curve or @code{GNUTLS_PK_UNKNOWN} .

@strong{Since:} 3.5.0
@end deftypefun

@subheading gnutls_ecc_curve_get_size
@anchor{gnutls_ecc_curve_get_size}
@deftypefun {int} {gnutls_ecc_curve_get_size} (gnutls_ecc_curve_t @var{curve})
@var{curve}: is an ECC curve


@strong{Returns:} the size in bytes of the curve or 0 on failure.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_ecc_curve_list
@anchor{gnutls_ecc_curve_list}
@deftypefun {const gnutls_ecc_curve_t *} {gnutls_ecc_curve_list} ( @var{void})

Get the list of supported elliptic curves.

This function is not thread safe.

@strong{Returns:} Return a (0)-terminated list of @code{gnutls_ecc_curve_t} 
integers indicating the available curves.
@end deftypefun

@subheading gnutls_ecc_curve_set_enabled
@anchor{gnutls_ecc_curve_set_enabled}
@deftypefun {int} {gnutls_ecc_curve_set_enabled} (gnutls_ecc_curve_t @var{curve}, unsigned int @var{enabled})
@var{curve}: is an ECC curve

@var{enabled}: whether to enable the curve

Modify the previous system wide setting that marked  @code{curve} as
enabled or disabled.  Calling this fuction is allowed
only if allowlisting mode is set in the configuration file,
and only if the system-wide TLS priority string
has not been initialized yet.
The intended usage is to provide applications with a way
to expressly deviate from the distribution or site defaults
inherited from the configuration file.
The modification is composable with further modifications
performed through the priority string mechanism.

This function is not thread-safe and is intended to be called
in the main thread at the beginning of the process execution.

@strong{Returns:} 0 on success or negative error code otherwise.

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_error_is_fatal
@anchor{gnutls_error_is_fatal}
@deftypefun {int} {gnutls_error_is_fatal} (int @var{error})
@var{error}: is a GnuTLS error code, a negative error code

If a GnuTLS function returns a negative error code you may feed that
value to this function to see if the error condition is fatal to
a TLS session (i.e., must be terminated).

Note that you may also want to check the error code manually, since some
non-fatal errors to the protocol (such as a warning alert or
a rehandshake request) may be fatal for your program.

This function is only useful if you are dealing with errors from
functions that relate to a TLS session (e.g., record layer or handshake
layer handling functions).

@strong{Returns:} Non-zero value on fatal errors or zero on non-fatal.
@end deftypefun

@subheading gnutls_error_to_alert
@anchor{gnutls_error_to_alert}
@deftypefun {int} {gnutls_error_to_alert} (int @var{err}, int * @var{level})
@var{err}: is a negative integer

@var{level}: the alert level will be stored there

Get an alert depending on the error code returned by a gnutls
function.  All alerts sent by this function should be considered
fatal.  The only exception is when  @code{err} is @code{GNUTLS_E_REHANDSHAKE} ,
where a warning alert should be sent to the peer indicating that no
renegotiation will be performed.

If there is no mapping to a valid alert the alert to indicate
internal error (@code{GNUTLS_A_INTERNAL_ERROR} ) is returned.

@strong{Returns:} the alert code to use for a particular error code.
@end deftypefun

@subheading gnutls_est_record_overhead_size
@anchor{gnutls_est_record_overhead_size}
@deftypefun {size_t} {gnutls_est_record_overhead_size} (gnutls_protocol_t @var{version}, gnutls_cipher_algorithm_t @var{cipher}, gnutls_mac_algorithm_t @var{mac}, gnutls_compression_method_t @var{comp}, unsigned int @var{flags})
@var{version}: is a @code{gnutls_protocol_t}  value

@var{cipher}: is a @code{gnutls_cipher_algorithm_t}  value

@var{mac}: is a @code{gnutls_mac_algorithm_t}  value

@var{comp}: is a @code{gnutls_compression_method_t}  value (ignored)

@var{flags}: must be zero

This function will return the set size in bytes of the overhead
due to TLS (or DTLS) per record.

Note that this function may provide inaccurate values when TLS
extensions that modify the record format are negotiated. In these
cases a more accurate value can be obtained using @code{gnutls_record_overhead_size()}  
after a completed handshake.

@strong{Since:} 3.2.2
@end deftypefun

@subheading gnutls_ext_get_current_msg
@anchor{gnutls_ext_get_current_msg}
@deftypefun {unsigned} {gnutls_ext_get_current_msg} (gnutls_session_t @var{session})
@var{session}: a @code{gnutls_session_t}  opaque pointer

This function allows an extension handler to obtain the message
this extension is being called from. The returned value is a single
entry of the @code{gnutls_ext_flags_t}  enumeration. That is, if an
extension was registered with the @code{GNUTLS_EXT_FLAG_HRR}  and
@code{GNUTLS_EXT_FLAG_EE}  flags, the value when called during parsing of the
encrypted extensions message will be @code{GNUTLS_EXT_FLAG_EE} .

If not called under an extension handler, its value is undefined.

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_ext_get_data
@anchor{gnutls_ext_get_data}
@deftypefun {int} {gnutls_ext_get_data} (gnutls_session_t @var{session}, unsigned @var{tls_id}, gnutls_ext_priv_data_t * @var{data})
@var{session}: a @code{gnutls_session_t}  opaque pointer

@var{tls_id}: the numeric id of the extension

@var{data}: a pointer to the private data to retrieve

This function retrieves any data previously stored with @code{gnutls_ext_set_data()} .

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_ext_get_name
@anchor{gnutls_ext_get_name}
@deftypefun {const char *} {gnutls_ext_get_name} (unsigned int @var{ext})
@var{ext}: is a TLS extension numeric ID

Convert a TLS extension numeric ID to a printable string.

@strong{Returns:} a pointer to a string that contains the name of the
specified cipher, or @code{NULL} .
@end deftypefun

@subheading gnutls_ext_get_name2
@anchor{gnutls_ext_get_name2}
@deftypefun {const char *} {gnutls_ext_get_name2} (gnutls_session_t @var{session}, unsigned int @var{tls_id}, gnutls_ext_parse_type_t @var{parse_point})
@var{session}: a @code{gnutls_session_t}  opaque pointer

@var{tls_id}: is a TLS extension numeric ID

@var{parse_point}: the parse type of the extension

Convert a TLS extension numeric ID to a printable string.

@strong{Returns:} a pointer to a string that contains the name of the
specified cipher, or @code{NULL} .
@end deftypefun

@subheading gnutls_ext_raw_parse
@anchor{gnutls_ext_raw_parse}
@deftypefun {int} {gnutls_ext_raw_parse} (void * @var{ctx}, gnutls_ext_raw_process_func @var{cb}, const gnutls_datum_t * @var{data}, unsigned int @var{flags})
@var{ctx}: a pointer to pass to callback function

@var{cb}: callback function to process each extension found

@var{data}: TLS extension data

@var{flags}: should be zero or @code{GNUTLS_EXT_RAW_FLAG_TLS_CLIENT_HELLO}  or @code{GNUTLS_EXT_RAW_FLAG_DTLS_CLIENT_HELLO} 

This function iterates through the TLS extensions as passed in
 @code{data} , passing the individual extension data to callback. The
 @code{data} must conform to Extension extensions<0..2^16-1> format.

If flags is @code{GNUTLS_EXT_RAW_TLS_FLAG_CLIENT_HELLO}  then this function
will parse the extension data from the position, as if the packet in
 @code{data} is a client hello (without record or handshake headers) -
as provided by @code{gnutls_handshake_set_hook_function()} .

The return value of the callback will be propagated.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code. On unknown
flags it returns @code{GNUTLS_E_INVALID_REQUEST} .

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_ext_register
@anchor{gnutls_ext_register}
@deftypefun {int} {gnutls_ext_register} (const char * @var{name}, int @var{id}, gnutls_ext_parse_type_t @var{parse_point}, gnutls_ext_recv_func @var{recv_func}, gnutls_ext_send_func @var{send_func}, gnutls_ext_deinit_data_func @var{deinit_func}, gnutls_ext_pack_func @var{pack_func}, gnutls_ext_unpack_func @var{unpack_func})
@var{name}: the name of the extension to register

@var{id}: the numeric TLS id of the extension

@var{parse_point}: the parse type of the extension (see gnutls_ext_parse_type_t)

@var{recv_func}: a function to receive the data

@var{send_func}: a function to send the data

@var{deinit_func}: a function deinitialize any private data

@var{pack_func}: a function which serializes the extension's private data (used on session packing for resumption)

@var{unpack_func}: a function which will deserialize the extension's private data

This function will register a new extension type. The extension will remain
registered until @code{gnutls_global_deinit()}  is called. If the extension type
is already registered then @code{GNUTLS_E_ALREADY_REGISTERED}  will be returned.

Each registered extension can store temporary data into the gnutls_session_t
structure using @code{gnutls_ext_set_data()} , and they can be retrieved using
@code{gnutls_ext_get_data()} .

Any extensions registered with this function are valid for the client
and TLS1.2 server hello (or encrypted extensions for TLS1.3).

This function is not thread safe.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_ext_set_data
@anchor{gnutls_ext_set_data}
@deftypefun {void} {gnutls_ext_set_data} (gnutls_session_t @var{session}, unsigned @var{tls_id}, gnutls_ext_priv_data_t @var{data})
@var{session}: a @code{gnutls_session_t}  opaque pointer

@var{tls_id}: the numeric id of the extension

@var{data}: the private data to set

This function allows an extension handler to store data in the current session
and retrieve them later on. The set data will be deallocated using
the gnutls_ext_deinit_data_func.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_fingerprint
@anchor{gnutls_fingerprint}
@deftypefun {int} {gnutls_fingerprint} (gnutls_digest_algorithm_t @var{algo}, const gnutls_datum_t * @var{data}, void * @var{result}, size_t * @var{result_size})
@var{algo}: is a digest algorithm

@var{data}: is the data

@var{result}: is the place where the result will be copied (may be null).

@var{result_size}: should hold the size of the result. The actual size
of the returned result will also be copied there.

This function will calculate a fingerprint (actually a hash), of
the given data.  The result is not printable data.  You should
convert it to hex, or to something else printable.

This is the usual way to calculate a fingerprint of an X.509 DER
encoded certificate.  Note however that the fingerprint of an
OpenPGP certificate is not just a hash and cannot be calculated with this
function.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_fips140_context_deinit
@anchor{gnutls_fips140_context_deinit}
@deftypefun {void} {gnutls_fips140_context_deinit} (gnutls_fips140_context_t @var{context})
@var{context}: a @code{gnutls_fips140_context_t} 

Uninitialize and release the FIPS context  @code{context} .

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_fips140_context_init
@anchor{gnutls_fips140_context_init}
@deftypefun {int} {gnutls_fips140_context_init} (gnutls_fips140_context_t * @var{context})
@var{context}: location to store  @code{gnutls_fips140_context_t} 

Create and initialize the FIPS context object.

@strong{Returns:} 0 upon success, a negative error code otherwise

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_fips140_get_operation_state
@anchor{gnutls_fips140_get_operation_state}
@deftypefun {gnutls_fips140_operation_state_t} {gnutls_fips140_get_operation_state} (gnutls_fips140_context_t @var{context})
@var{context}: a @code{gnutls_fips140_context_t} 

Get the previous operation state of  @code{context} in terms of FIPS.

@strong{Returns:} a @code{gnutls_fips140_operation_state_t} 

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_fips140_mode_enabled
@anchor{gnutls_fips140_mode_enabled}
@deftypefun {unsigned} {gnutls_fips140_mode_enabled} ( @var{void})

Checks whether this library is in FIPS140 mode. The returned
value corresponds to the library mode as set with
@code{gnutls_fips140_set_mode()} .

If @code{gnutls_fips140_set_mode()}  was called with @code{GNUTLS_FIPS140_SET_MODE_THREAD} 
then this function will return the current thread's FIPS140 mode, otherwise
the global value is returned.

@strong{Returns:} return non-zero if true or zero if false.

@strong{Since:} 3.3.0
@end deftypefun

@subheading gnutls_fips140_pop_context
@anchor{gnutls_fips140_pop_context}
@deftypefun {int} {gnutls_fips140_pop_context} ( @var{void})

Dissociate the FIPS context currently
active on the current thread, reverting to the previously active
context. If a cryptographic operation is ongoing in the current
thread, e.g., @code{gnutls_aead_cipher_init()}  is called but
@code{gnutls_aead_cipher_deinit()}  is not yet called, it returns an error
@code{GNUTLS_E_INVALID_REQUEST} .

This function is no-op if FIPS140 is not compiled in nor enabled
at run-time.

@strong{Returns:} 0 upon success, a negative error code otherwise

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_fips140_push_context
@anchor{gnutls_fips140_push_context}
@deftypefun {int} {gnutls_fips140_push_context} (gnutls_fips140_context_t @var{context})
@var{context}: a @code{gnutls_fips140_context_t} 

Associate the FIPS  @code{context} to the current thread, diverting the
currently active context. If a cryptographic operation is ongoing
in the current thread, e.g., @code{gnutls_aead_cipher_init()}  is called
but @code{gnutls_aead_cipher_deinit()}  is not yet called, it returns an
error @code{GNUTLS_E_INVALID_REQUEST} .

The operation state of  @code{context} will be reset to
@code{GNUTLS_FIPS140_OP_INITIAL} .

This function is no-op if FIPS140 is not compiled in nor enabled
at run-time.

@strong{Returns:} 0 upon success, a negative error code otherwise

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_fips140_run_self_tests
@anchor{gnutls_fips140_run_self_tests}
@deftypefun {int} {gnutls_fips140_run_self_tests} ( @var{void})

Manually perform the second round of the FIPS140 self-tests,
including:

- Known answer tests (KAT) for the selected set of symmetric
cipher, MAC, public key, KDF, and DRBG
- Library integrity checks

Upon failure with FIPS140 mode enabled, it makes the library
unusable.  This function is not thread-safe.

@strong{Returns:} 0 upon success, a negative error code otherwise

@strong{Since:} 3.7.7
@end deftypefun

@subheading gnutls_fips140_set_mode
@anchor{gnutls_fips140_set_mode}
@deftypefun {void} {gnutls_fips140_set_mode} (gnutls_fips_mode_t @var{mode}, unsigned @var{flags})
@var{mode}: the FIPS140-2 mode to switch to

@var{flags}: should be zero or @code{GNUTLS_FIPS140_SET_MODE_THREAD} 

That function is not thread-safe when changing the mode with no flags
(globally), and should be called prior to creating any threads. Its
behavior with no flags after threads are created is undefined.

When the flag @code{GNUTLS_FIPS140_SET_MODE_THREAD}  is specified
then this call will change the FIPS140-2 mode for this particular
thread and not for the whole process. That way an application
can utilize this function to set and reset mode for specific
operations.

This function never fails but will be a no-op if used when
the library is not in FIPS140-2 mode. When asked to switch to unknown
values for  @code{mode} or to @code{GNUTLS_FIPS140_SELFTESTS}  mode, the library
switches to @code{GNUTLS_FIPS140_STRICT}  mode.

@strong{Since:} 3.6.2
@end deftypefun

@subheading gnutls_get_library_config
@anchor{gnutls_get_library_config}
@deftypefun {const gnutls_library_config_st *} {gnutls_get_library_config} ( @var{void})

Returns the library configuration as key value pairs.
Currently defined keys are:

- fips-module-name: the name of the FIPS140 module

- fips-module-version: the version of the FIPS140 module

- libgnutls-soname: the SONAME of the library itself

- libnettle-soname: the library SONAME of linked libnettle

- libhogweed-soname: the library SONAME of linked libhogweed

- libgmp-soname: the library SONAME of linked libgmp

- hardware-features: enabled hardware support features

- tls-features: enabled TLS protocol features

@strong{Returns:} a NUL-terminated @code{gnutls_library_config_st}  array

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_get_system_config_file
@anchor{gnutls_get_system_config_file}
@deftypefun {const char *} {gnutls_get_system_config_file} ( @var{void})

Returns the filename of the system wide configuration
file to be loaded by the library.

@strong{Returns:} a constant pointer to the config file path

@strong{Since:} 3.6.9
@end deftypefun

@subheading gnutls_global_deinit
@anchor{gnutls_global_deinit}
@deftypefun {void} {gnutls_global_deinit} ( @var{void})

This function deinitializes the global data, that were initialized
using @code{gnutls_global_init()} .

Since GnuTLS 3.3.0 this function is no longer necessary to be explicitly
called. GnuTLS will automatically deinitialize on library destructor. See
@code{gnutls_global_init()}  for disabling the implicit initialization/deinitialization.
@end deftypefun

@subheading gnutls_global_init
@anchor{gnutls_global_init}
@deftypefun {int} {gnutls_global_init} ( @var{void})

Since GnuTLS 3.3.0 this function is no longer necessary to be explicitly
called. To disable the implicit call (in a library constructor) of this
function set the environment variable @code{GNUTLS_NO_IMPLICIT_INIT}  to 1.

This function performs any required precalculations, detects
the supported CPU capabilities and initializes the underlying
cryptographic backend. In order to free any resources 
taken by this call you should @code{gnutls_global_deinit()}  
when gnutls usage is no longer needed.

This function increments a global counter, so that
@code{gnutls_global_deinit()}  only releases resources when it has been
called as many times as @code{gnutls_global_init()} .  This is useful when
GnuTLS is used by more than one library in an application.  This
function can be called many times, but will only do something the
first time. It is thread safe since GnuTLS 3.3.0.

A subsequent call of this function if the initial has failed will
return the same error code.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_global_set_audit_log_function
@anchor{gnutls_global_set_audit_log_function}
@deftypefun {void} {gnutls_global_set_audit_log_function} (gnutls_audit_log_func @var{log_func})
@var{log_func}: it is the audit log function

This is the function to set the audit logging function. This
is a function to report important issues, such as possible
attacks in the protocol. This is different from @code{gnutls_global_set_log_function()} 
because it will report also session-specific events. The session
parameter will be null if there is no corresponding TLS session.

 @code{gnutls_audit_log_func} is of the form,
void (*gnutls_audit_log_func)( gnutls_session_t, const char*);

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_global_set_log_function
@anchor{gnutls_global_set_log_function}
@deftypefun {void} {gnutls_global_set_log_function} (gnutls_log_func @var{log_func})
@var{log_func}: it's a log function

This is the function where you set the logging function gnutls is
going to use.  This function only accepts a character array.
Normally you may not use this function since it is only used for
debugging purposes.

 @code{gnutls_log_func} is of the form,
void (*gnutls_log_func)( int level, const char*);
@end deftypefun

@subheading gnutls_global_set_log_level
@anchor{gnutls_global_set_log_level}
@deftypefun {void} {gnutls_global_set_log_level} (int @var{level})
@var{level}: it's an integer from 0 to 99.

This is the function that allows you to set the log level.  The
level is an integer between 0 and 9.  Higher values mean more
verbosity. The default value is 0.  Larger values should only be
used with care, since they may reveal sensitive information.

Use a log level over 10 to enable all debugging options.
@end deftypefun

@subheading gnutls_global_set_mutex
@anchor{gnutls_global_set_mutex}
@deftypefun {void} {gnutls_global_set_mutex} (mutex_init_func @var{init}, mutex_deinit_func @var{deinit}, mutex_lock_func @var{lock}, mutex_unlock_func @var{unlock})
@var{init}: mutex initialization function

@var{deinit}: mutex deinitialization function

@var{lock}: mutex locking function

@var{unlock}: mutex unlocking function

With this function you are allowed to override the default mutex
locks used in some parts of gnutls and dependent libraries. This function
should be used if you have complete control of your program and libraries.
Do not call this function from a library, or preferably from any application
unless really needed to. GnuTLS will use the appropriate locks for the running
system.

This function must be called prior to any other GnuTLS function; otherwise
the behavior is undefined.

@strong{Deprecated:} This function is discouraged on GnuTLS 3.7.3 or later.

@strong{Since:} 2.12.0
@end deftypefun

@subheading gnutls_global_set_time_function
@anchor{gnutls_global_set_time_function}
@deftypefun {void} {gnutls_global_set_time_function} (gnutls_time_func @var{time_func})
@var{time_func}: it's the system time function, a @code{gnutls_time_func()}  callback.

This is the function where you can override the default system time
function.  The application provided function should behave the same
as the standard function.

@strong{Since:} 2.12.0
@end deftypefun

@subheading gnutls_gost_paramset_get_name
@anchor{gnutls_gost_paramset_get_name}
@deftypefun {const char *} {gnutls_gost_paramset_get_name} (gnutls_gost_paramset_t @var{param})
@var{param}: is a GOST 28147 param set

Convert a @code{gnutls_gost_paramset_t}  value to a string.

@strong{Returns:} a string that contains the name of the specified GOST param set,
or @code{NULL} .

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_gost_paramset_get_oid
@anchor{gnutls_gost_paramset_get_oid}
@deftypefun {const char *} {gnutls_gost_paramset_get_oid} (gnutls_gost_paramset_t @var{param})
@var{param}: is a GOST 28147 param set

Convert a @code{gnutls_gost_paramset_t}  value to its object identifier.

@strong{Returns:} a string that contains the object identifier of the specified GOST
param set, or @code{NULL} .

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_group_get
@anchor{gnutls_group_get}
@deftypefun {gnutls_group_t} {gnutls_group_get} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Returns the currently used group for key exchange. Only valid
when using an elliptic curve or DH ciphersuite.

@strong{Returns:} the currently used group, a @code{gnutls_group_t} 
type.

@strong{Since:} 3.6.0
@end deftypefun

@subheading gnutls_group_get_id
@anchor{gnutls_group_get_id}
@deftypefun {gnutls_group_t} {gnutls_group_get_id} (const char * @var{name})
@var{name}: is a group name

The names are compared in a case insensitive way.

@strong{Returns:} return a @code{gnutls_group_t}  value corresponding to
the specified group, or @code{GNUTLS_GROUP_INVALID}  on error.

@strong{Since:} 3.6.0
@end deftypefun

@subheading gnutls_group_get_name
@anchor{gnutls_group_get_name}
@deftypefun {const char *} {gnutls_group_get_name} (gnutls_group_t @var{group})
@var{group}: is an element from @code{gnutls_group_t} 

Convert a @code{gnutls_group_t}  value to a string.

@strong{Returns:} a string that contains the name of the specified
group or @code{NULL} .

@strong{Since:} 3.6.0
@end deftypefun

@subheading gnutls_group_list
@anchor{gnutls_group_list}
@deftypefun {const gnutls_group_t *} {gnutls_group_list} ( @var{void})

Get the list of supported elliptic curves.

This function is not thread safe.

@strong{Returns:} Return a (0)-terminated list of @code{gnutls_group_t} 
integers indicating the available groups.

@strong{Since:} 3.6.0
@end deftypefun

@subheading gnutls_handshake
@anchor{gnutls_handshake}
@deftypefun {int} {gnutls_handshake} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function performs the handshake of the TLS/SSL protocol, and
initializes the TLS session parameters.

The non-fatal errors expected by this function are:
@code{GNUTLS_E_INTERRUPTED} , @code{GNUTLS_E_AGAIN} ,
@code{GNUTLS_E_WARNING_ALERT_RECEIVED} . When this function is called
for re-handshake under TLS 1.2 or earlier, the non-fatal error code
@code{GNUTLS_E_GOT_APPLICATION_DATA}  may also be returned.

The former two interrupt the handshake procedure due to the transport
layer being interrupted, and the latter because of a "warning" alert that
was sent by the peer (it is always a good idea to check any
received alerts). On these non-fatal errors call this function again,
until it returns 0; cf.  @code{gnutls_record_get_direction()}  and
@code{gnutls_error_is_fatal()} . In DTLS sessions the non-fatal error
@code{GNUTLS_E_LARGE_PACKET}  is also possible, and indicates that
the MTU should be adjusted.

When this function is called by a server after a rehandshake request
under TLS 1.2 or earlier the @code{GNUTLS_E_GOT_APPLICATION_DATA}  error code indicates
that some data were pending prior to peer initiating the handshake.
Under TLS 1.3 this function when called after a successful handshake, is a no-op
and always succeeds in server side; in client side this function is
equivalent to @code{gnutls_session_key_update()}  with @code{GNUTLS_KU_PEER}  flag.

This function handles both full and abbreviated TLS handshakes (resumption).
For abbreviated handshakes, in client side, the @code{gnutls_session_set_data()} 
should be called prior to this function to set parameters from a previous session.
In server side, resumption is handled by either setting a DB back-end, or setting
up keys for session tickets.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on a successful handshake, otherwise a negative error code.
@end deftypefun

@subheading gnutls_handshake_description_get_name
@anchor{gnutls_handshake_description_get_name}
@deftypefun {const char     *} {gnutls_handshake_description_get_name} (gnutls_handshake_description_t         @var{type})
@var{type}: is a handshake message description

Convert a @code{gnutls_handshake_description_t}  value to a string.

@strong{Returns:} a string that contains the name of the specified handshake
message or @code{NULL} .
@end deftypefun

@subheading gnutls_handshake_get_last_in
@anchor{gnutls_handshake_get_last_in}
@deftypefun {gnutls_handshake_description_t} {gnutls_handshake_get_last_in} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function is only useful to check where the last performed
handshake failed.  If the previous handshake succeed or was not
performed at all then no meaningful value will be returned.

Check @code{gnutls_handshake_description_t}  in gnutls.h for the
available handshake descriptions.

@strong{Returns:} the last handshake message type received, a
@code{gnutls_handshake_description_t} .
@end deftypefun

@subheading gnutls_handshake_get_last_out
@anchor{gnutls_handshake_get_last_out}
@deftypefun {gnutls_handshake_description_t} {gnutls_handshake_get_last_out} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function is only useful to check where the last performed
handshake failed.  If the previous handshake succeed or was not
performed at all then no meaningful value will be returned.

Check @code{gnutls_handshake_description_t}  in gnutls.h for the
available handshake descriptions.

@strong{Returns:} the last handshake message type sent, a
@code{gnutls_handshake_description_t} .
@end deftypefun

@subheading gnutls_handshake_set_hook_function
@anchor{gnutls_handshake_set_hook_function}
@deftypefun {void} {gnutls_handshake_set_hook_function} (gnutls_session_t @var{session}, unsigned int @var{htype}, int @var{when}, gnutls_handshake_hook_func @var{func})
@var{session}: is a @code{gnutls_session_t}  type

@var{htype}: the @code{gnutls_handshake_description_t}  of the message to hook at

@var{when}: @code{GNUTLS_HOOK_} * depending on when the hook function should be called

@var{func}: is the function to be called

This function will set a callback to be called after or before the specified
handshake message has been received or generated. This is a
generalization of @code{gnutls_handshake_set_post_client_hello_function()} .

To call the hook function prior to the message being generated or processed
use @code{GNUTLS_HOOK_PRE}  as  @code{when} parameter, @code{GNUTLS_HOOK_POST}  to call
after, and @code{GNUTLS_HOOK_BOTH}  for both cases.

This callback must return 0 on success or a gnutls error code to
terminate the handshake.

To hook at all handshake messages use an  @code{htype} of @code{GNUTLS_HANDSHAKE_ANY} .

@strong{Warning:} You should not use this function to terminate the
handshake based on client input unless you know what you are
doing. Before the handshake is finished there is no way to know if
there is a man-in-the-middle attack being performed.
@end deftypefun

@subheading gnutls_handshake_set_max_packet_length
@anchor{gnutls_handshake_set_max_packet_length}
@deftypefun {void} {gnutls_handshake_set_max_packet_length} (gnutls_session_t @var{session}, size_t @var{max})
@var{session}: is a @code{gnutls_session_t}  type.

@var{max}: is the maximum number.

This function will set the maximum size of all handshake messages.
Handshakes over this size are rejected with
@code{GNUTLS_E_HANDSHAKE_TOO_LARGE}  error code.  The default value is
128kb which is typically large enough.  Set this to 0 if you do not
want to set an upper limit.

The reason for restricting the handshake message sizes are to
limit Denial of Service attacks.

Note that the maximum handshake size was increased to 128kb
from 48kb in GnuTLS 3.5.5.
@end deftypefun

@subheading gnutls_handshake_set_post_client_hello_function
@anchor{gnutls_handshake_set_post_client_hello_function}
@deftypefun {void} {gnutls_handshake_set_post_client_hello_function} (gnutls_session_t @var{session}, gnutls_handshake_simple_hook_func @var{func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{func}: is the function to be called

This function will set a callback to be called after the client
hello has been received (callback valid in server side only). This
allows the server to adjust settings based on received extensions.

Those settings could be ciphersuites, requesting certificate, or
anything else except for version negotiation (this is done before
the hello message is parsed).

This callback must return 0 on success or a gnutls error code to
terminate the handshake.

Since GnuTLS 3.3.5 the callback is
allowed to return @code{GNUTLS_E_AGAIN}  or @code{GNUTLS_E_INTERRUPTED}  to
put the handshake on hold. In that case @code{gnutls_handshake()} 
will return @code{GNUTLS_E_INTERRUPTED}  and can be resumed when needed.

@strong{Warning:} You should not use this function to terminate the
handshake based on client input unless you know what you are
doing. Before the handshake is finished there is no way to know if
there is a man-in-the-middle attack being performed.
@end deftypefun

@subheading gnutls_handshake_set_private_extensions
@anchor{gnutls_handshake_set_private_extensions}
@deftypefun {void} {gnutls_handshake_set_private_extensions} (gnutls_session_t @var{session}, int @var{allow})
@var{session}: is a @code{gnutls_session_t}  type.

@var{allow}: is an integer (0 or 1)

This function will enable or disable the use of private cipher
suites (the ones that start with 0xFF).  By default or if  @code{allow} is 0 then these cipher suites will not be advertised nor used.

Currently GnuTLS does not include such cipher-suites or
compression algorithms.

Enabling the private ciphersuites when talking to other than
gnutls servers and clients may cause interoperability problems.
@end deftypefun

@subheading gnutls_handshake_set_random
@anchor{gnutls_handshake_set_random}
@deftypefun {int} {gnutls_handshake_set_random} (gnutls_session_t @var{session}, const gnutls_datum_t * @var{random})
@var{session}: is a @code{gnutls_session_t}  type.

@var{random}: a random value of 32-bytes

This function will explicitly set the server or client hello 
random value in the subsequent TLS handshake. The random value 
should be a 32-byte value.

Note that this function should not normally be used as gnutls
will select automatically a random value for the handshake.

This function should not be used when resuming a session.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.

Since 3.1.9
@end deftypefun

@subheading gnutls_handshake_set_read_function
@anchor{gnutls_handshake_set_read_function}
@deftypefun {void} {gnutls_handshake_set_read_function} (gnutls_session_t @var{session}, gnutls_handshake_read_func @var{func})
@var{session}: is @code{gnutls_session_t}  type

@var{func}: is the function to be called

This function will set a callback to be called when a handshake
message is being sent.

@strong{Since:} 3.7.0
@end deftypefun

@subheading gnutls_handshake_set_secret_function
@anchor{gnutls_handshake_set_secret_function}
@deftypefun {void} {gnutls_handshake_set_secret_function} (gnutls_session_t @var{session}, gnutls_handshake_secret_func @var{func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{func}: the secret func

This function will set a callback to be called when a new traffic
secret is installed.

@strong{Since:} 3.7.0
@end deftypefun

@subheading gnutls_handshake_set_timeout
@anchor{gnutls_handshake_set_timeout}
@deftypefun {void} {gnutls_handshake_set_timeout} (gnutls_session_t @var{session}, unsigned int @var{ms})
@var{session}: is a @code{gnutls_session_t}  type.

@var{ms}: is a timeout value in milliseconds

This function sets the timeout for the TLS handshake process
to the provided value. Use an  @code{ms} value of zero to disable
timeout, or @code{GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT}  for a reasonable
default value. For the DTLS protocol, the more detailed
@code{gnutls_dtls_set_timeouts()}  is provided.

This function requires to set a pull timeout callback. See
@code{gnutls_transport_set_pull_timeout_function()} .

@strong{Since:} 3.1.0
@end deftypefun

@subheading gnutls_handshake_write
@anchor{gnutls_handshake_write}
@deftypefun {int} {gnutls_handshake_write} (gnutls_session_t @var{session}, gnutls_record_encryption_level_t @var{level}, const void * @var{data}, size_t @var{data_size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{level}: the current encryption level for reading a handshake message

@var{data}: the (const) handshake data to be processed

@var{data_size}: the size of data

This function processes a handshake message in the encryption level
specified with  @code{level} . Prior to calling this function, a handshake
read callback must be set on  @code{session} . Use
@code{gnutls_handshake_set_read_function()}  to do this.

@strong{Since:} 3.7.0
@end deftypefun

@subheading gnutls_heartbeat_allowed
@anchor{gnutls_heartbeat_allowed}
@deftypefun {unsigned} {gnutls_heartbeat_allowed} (gnutls_session_t @var{session}, unsigned int @var{type})
@var{session}: is a @code{gnutls_session_t}  type.

@var{type}: one of @code{GNUTLS_HB_LOCAL_ALLOWED_TO_SEND}  and @code{GNUTLS_HB_PEER_ALLOWED_TO_SEND} 

This function will check whether heartbeats are allowed
to be sent or received in this session. 

@strong{Returns:} Non zero if heartbeats are allowed.

@strong{Since:} 3.1.2
@end deftypefun

@subheading gnutls_heartbeat_enable
@anchor{gnutls_heartbeat_enable}
@deftypefun {void} {gnutls_heartbeat_enable} (gnutls_session_t @var{session}, unsigned int @var{type})
@var{session}: is a @code{gnutls_session_t}  type.

@var{type}: one of the GNUTLS_HB_* flags

If this function is called with the @code{GNUTLS_HB_PEER_ALLOWED_TO_SEND} 
 @code{type} , GnuTLS will allow heartbeat messages to be received. Moreover it also
request the peer to accept heartbeat messages. This function
must be called prior to TLS handshake.

If the  @code{type} used is @code{GNUTLS_HB_LOCAL_ALLOWED_TO_SEND} , then the peer
will be asked to accept heartbeat messages but not send ones.

The function @code{gnutls_heartbeat_allowed()}  can be used to test Whether
locally generated heartbeat messages can be accepted by the peer.

@strong{Since:} 3.1.2
@end deftypefun

@subheading gnutls_heartbeat_get_timeout
@anchor{gnutls_heartbeat_get_timeout}
@deftypefun {unsigned int} {gnutls_heartbeat_get_timeout} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function will return the milliseconds remaining
for a retransmission of the previously sent ping
message. This function is useful when ping is used in
non-blocking mode, to estimate when to call @code{gnutls_heartbeat_ping()} 
if no packets have been received.

@strong{Returns:} the remaining time in milliseconds.

@strong{Since:} 3.1.2
@end deftypefun

@subheading gnutls_heartbeat_ping
@anchor{gnutls_heartbeat_ping}
@deftypefun {int} {gnutls_heartbeat_ping} (gnutls_session_t @var{session}, size_t @var{data_size}, unsigned int @var{max_tries}, unsigned int @var{flags})
@var{session}: is a @code{gnutls_session_t}  type.

@var{data_size}: is the length of the ping payload.

@var{max_tries}: if flags is @code{GNUTLS_HEARTBEAT_WAIT}  then this sets the number of retransmissions. Use zero for indefinite (until timeout).

@var{flags}: if @code{GNUTLS_HEARTBEAT_WAIT}  then wait for pong or timeout instead of returning immediately.

This function sends a ping to the peer. If the  @code{flags} is set
to @code{GNUTLS_HEARTBEAT_WAIT}  then it waits for a reply from the peer.

Note that it is highly recommended to use this function with the
flag @code{GNUTLS_HEARTBEAT_WAIT} , or you need to handle retransmissions
and timeouts manually.

The total TLS data transmitted as part of the ping message are given by
the following formula: MAX(16,  @code{data_size} )+@code{gnutls_record_overhead_size()} +3.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.1.2
@end deftypefun

@subheading gnutls_heartbeat_pong
@anchor{gnutls_heartbeat_pong}
@deftypefun {int} {gnutls_heartbeat_pong} (gnutls_session_t @var{session}, unsigned int @var{flags})
@var{session}: is a @code{gnutls_session_t}  type.

@var{flags}: should be zero

This function replies to a ping by sending a pong to the peer.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.1.2
@end deftypefun

@subheading gnutls_heartbeat_set_timeouts
@anchor{gnutls_heartbeat_set_timeouts}
@deftypefun {void} {gnutls_heartbeat_set_timeouts} (gnutls_session_t @var{session}, unsigned int @var{retrans_timeout}, unsigned int @var{total_timeout})
@var{session}: is a @code{gnutls_session_t}  type.

@var{retrans_timeout}: The time at which a retransmission will occur in milliseconds

@var{total_timeout}: The time at which the connection will be aborted, in milliseconds.

This function will override the timeouts for the DTLS heartbeat
protocol. The retransmission timeout is the time after which a
message from the peer is not received, the previous request will
be retransmitted. The total timeout is the time after which the
handshake will be aborted with @code{GNUTLS_E_TIMEDOUT} .

@strong{Since:} 3.1.2
@end deftypefun

@subheading gnutls_hex2bin
@anchor{gnutls_hex2bin}
@deftypefun {int} {gnutls_hex2bin} (const char * @var{hex_data}, size_t @var{hex_size}, void * @var{bin_data}, size_t * @var{bin_size})
@var{hex_data}: string with data in hex format

@var{hex_size}: size of hex data

@var{bin_data}: output array with binary data

@var{bin_size}: when calling should hold maximum size of  @code{bin_data} ,
on return will hold actual length of  @code{bin_data} .

Convert a buffer with hex data to binary data. This function
unlike @code{gnutls_hex_decode()}  can parse hex data with separators
between numbers. That is, it ignores any non-hex characters.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 2.4.0
@end deftypefun

@subheading gnutls_hex_decode
@anchor{gnutls_hex_decode}
@deftypefun {int} {gnutls_hex_decode} (const gnutls_datum_t * @var{hex_data}, void * @var{result}, size_t * @var{result_size})
@var{hex_data}: contain the encoded data

@var{result}: the place where decoded data will be copied

@var{result_size}: holds the size of the result

This function will decode the given encoded data, using the hex
encoding used by PSK password files.

Initially  @code{result_size} must hold the maximum size available in
 @code{result} , and on return it will contain the number of bytes written.

@strong{Returns:} @code{GNUTLS_E_SHORT_MEMORY_BUFFER}  if the buffer given is not
long enough, @code{GNUTLS_E_PARSING_ERROR}  on invalid hex data, or 0 on success.
@end deftypefun

@subheading gnutls_hex_decode2
@anchor{gnutls_hex_decode2}
@deftypefun {int} {gnutls_hex_decode2} (const gnutls_datum_t * @var{hex_data}, gnutls_datum_t * @var{result})
@var{hex_data}: contain the encoded data

@var{result}: the result in an allocated string

This function will decode the given encoded data, using the hex
encoding used by PSK password files.

@strong{Returns:} @code{GNUTLS_E_PARSING_ERROR}  on invalid hex data, or 0 on success.
@end deftypefun

@subheading gnutls_hex_encode
@anchor{gnutls_hex_encode}
@deftypefun {int} {gnutls_hex_encode} (const gnutls_datum_t * @var{data}, char * @var{result}, size_t * @var{result_size})
@var{data}: contain the raw data

@var{result}: the place where hex data will be copied

@var{result_size}: holds the size of the result

This function will convert the given data to printable data, using
the hex encoding, as used in the PSK password files.

Note that the size of the result includes the null terminator.

@strong{Returns:} @code{GNUTLS_E_SHORT_MEMORY_BUFFER}  if the buffer given is not
long enough, or 0 on success.
@end deftypefun

@subheading gnutls_hex_encode2
@anchor{gnutls_hex_encode2}
@deftypefun {int} {gnutls_hex_encode2} (const gnutls_datum_t * @var{data}, gnutls_datum_t * @var{result})
@var{data}: contain the raw data

@var{result}: the result in an allocated string

This function will convert the given data to printable data, using
the hex encoding, as used in the PSK password files.

Note that the size of the result does NOT include the null terminator.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.
@end deftypefun

@subheading gnutls_idna_map
@anchor{gnutls_idna_map}
@deftypefun {int} {gnutls_idna_map} (const char * @var{input}, unsigned @var{ilen}, gnutls_datum_t * @var{out}, unsigned @var{flags})
@var{input}: contain the UTF-8 formatted domain name

@var{ilen}: the length of the provided string

@var{out}: the result in an null-terminated allocated string

@var{flags}: should be zero

This function will convert the provided UTF-8 domain name, to
its IDNA mapping in an allocated variable. Note that depending on the flags the used gnutls
library was compiled with, the output of this function may vary (i.e.,
may be IDNA2008, or IDNA2003).

To force IDNA2008 specify the flag @code{GNUTLS_IDNA_FORCE_2008} . In
the case GnuTLS is not compiled with the necessary dependencies,
@code{GNUTLS_E_UNIMPLEMENTED_FEATURE}  will be returned to indicate that
gnutls is unable to perform the requested conversion.

Note also, that this function will return an empty string if an
empty string is provided as input.

@strong{Returns:} @code{GNUTLS_E_INVALID_UTF8_STRING}  on invalid UTF-8 data, or 0 on success.

@strong{Since:} 3.5.8
@end deftypefun

@subheading gnutls_idna_reverse_map
@anchor{gnutls_idna_reverse_map}
@deftypefun {int} {gnutls_idna_reverse_map} (const char * @var{input}, unsigned @var{ilen}, gnutls_datum_t * @var{out}, unsigned @var{flags})
@var{input}: contain the ACE (IDNA) formatted domain name

@var{ilen}: the length of the provided string

@var{out}: the result in an null-terminated allocated UTF-8 string

@var{flags}: should be zero

This function will convert an ACE (ASCII-encoded) domain name to a UTF-8 domain name.

If GnuTLS is compiled without IDNA support, then this function
will return @code{GNUTLS_E_UNIMPLEMENTED_FEATURE} .

Note also, that this function will return an empty string if an
empty string is provided as input.

@strong{Returns:} A negative error code on error, or 0 on success.

@strong{Since:} 3.5.8
@end deftypefun

@subheading gnutls_init
@anchor{gnutls_init}
@deftypefun {int} {gnutls_init} (gnutls_session_t * @var{session}, unsigned int @var{flags})
@var{session}: is a pointer to a @code{gnutls_session_t}  type.

@var{flags}: indicate if this session is to be used for server or client.

This function initializes the provided session. Every
session must be initialized before use, and must be deinitialized
after used by calling @code{gnutls_deinit()} .

 @code{flags} can be any combination of flags from @code{gnutls_init_flags_t} .

Note that since version 3.1.2 this function enables some common
TLS extensions such as session tickets and OCSP certificate status
request in client side by default. To prevent that use the @code{GNUTLS_NO_EXTENSIONS} 
flag.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.
@end deftypefun

@subheading gnutls_key_generate
@anchor{gnutls_key_generate}
@deftypefun {int} {gnutls_key_generate} (gnutls_datum_t * @var{key}, unsigned int @var{key_size})
@var{key}: is a pointer to a @code{gnutls_datum_t}  which will contain a newly
created key

@var{key_size}: the number of bytes of the key

Generates a random key of  @code{key_size} bytes.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, or an
error code.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_kx_get
@anchor{gnutls_kx_get}
@deftypefun {gnutls_kx_algorithm_t} {gnutls_kx_get} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get the currently used key exchange algorithm.

This function will return @code{GNUTLS_KX_ECDHE_RSA} , or @code{GNUTLS_KX_DHE_RSA} 
under TLS 1.3, to indicate an elliptic curve DH key exchange or
a finite field one. The precise group used is available
by calling @code{gnutls_group_get()}  instead.

@strong{Returns:} the key exchange algorithm used in the last handshake, a
@code{gnutls_kx_algorithm_t}  value.
@end deftypefun

@subheading gnutls_kx_get_id
@anchor{gnutls_kx_get_id}
@deftypefun {gnutls_kx_algorithm_t} {gnutls_kx_get_id} (const char * @var{name})
@var{name}: is a KX name

Convert a string to a @code{gnutls_kx_algorithm_t}  value.  The names are
compared in a case insensitive way.

@strong{Returns:} an id of the specified KX algorithm, or @code{GNUTLS_KX_UNKNOWN} 
on error.
@end deftypefun

@subheading gnutls_kx_get_name
@anchor{gnutls_kx_get_name}
@deftypefun {const char *} {gnutls_kx_get_name} (gnutls_kx_algorithm_t @var{algorithm})
@var{algorithm}: is a key exchange algorithm

Convert a @code{gnutls_kx_algorithm_t}  value to a string.

@strong{Returns:} a pointer to a string that contains the name of the
specified key exchange algorithm, or @code{NULL} .
@end deftypefun

@subheading gnutls_kx_list
@anchor{gnutls_kx_list}
@deftypefun {const gnutls_kx_algorithm_t *} {gnutls_kx_list} ( @var{void})

Get a list of supported key exchange algorithms.

This function is not thread safe.

@strong{Returns:} a (0)-terminated list of @code{gnutls_kx_algorithm_t}  integers
indicating the available key exchange algorithms.
@end deftypefun

@subheading gnutls_load_file
@anchor{gnutls_load_file}
@deftypefun {int} {gnutls_load_file} (const char * @var{filename}, gnutls_datum_t * @var{data})
@var{filename}: the name of the file to load

@var{data}: Where the file will be stored

This function will load a file into a datum. The data are
zero terminated but the terminating null is not included in length.
The returned data are allocated using @code{gnutls_malloc()} .

Note that this function is not designed for reading sensitive materials,
such as private keys, on practical applications. When the reading fails
in the middle, the partially loaded content might remain on memory.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.

Since 3.1.0
@end deftypefun

@subheading gnutls_mac_get
@anchor{gnutls_mac_get}
@deftypefun {gnutls_mac_algorithm_t} {gnutls_mac_get} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get the currently used MAC algorithm.

@strong{Returns:} the currently used mac algorithm, a
@code{gnutls_mac_algorithm_t}  value.
@end deftypefun

@subheading gnutls_mac_get_id
@anchor{gnutls_mac_get_id}
@deftypefun {gnutls_mac_algorithm_t} {gnutls_mac_get_id} (const char * @var{name})
@var{name}: is a MAC algorithm name

Convert a string to a @code{gnutls_mac_algorithm_t}  value.  The names are
compared in a case insensitive way.

@strong{Returns:} a @code{gnutls_mac_algorithm_t}  id of the specified MAC
algorithm string, or @code{GNUTLS_MAC_UNKNOWN}  on failure.
@end deftypefun

@subheading gnutls_mac_get_key_size
@anchor{gnutls_mac_get_key_size}
@deftypefun {size_t} {gnutls_mac_get_key_size} (gnutls_mac_algorithm_t @var{algorithm})
@var{algorithm}: is an encryption algorithm

Returns the size of the MAC key used in TLS.

@strong{Returns:} length (in bytes) of the given MAC key size, or 0 if the
given MAC algorithm is invalid.
@end deftypefun

@subheading gnutls_mac_get_name
@anchor{gnutls_mac_get_name}
@deftypefun {const char *} {gnutls_mac_get_name} (gnutls_mac_algorithm_t @var{algorithm})
@var{algorithm}: is a MAC algorithm

Convert a @code{gnutls_mac_algorithm_t}  value to a string.

@strong{Returns:} a string that contains the name of the specified MAC
algorithm, or @code{NULL} .
@end deftypefun

@subheading gnutls_mac_list
@anchor{gnutls_mac_list}
@deftypefun {const gnutls_mac_algorithm_t *} {gnutls_mac_list} ( @var{void})

Get a list of hash algorithms for use as MACs.  Note that not
necessarily all MACs are supported in TLS cipher suites.
This function is not thread safe.

@strong{Returns:} Return a (0)-terminated list of @code{gnutls_mac_algorithm_t} 
integers indicating the available MACs.
@end deftypefun

@subheading gnutls_memcmp
@anchor{gnutls_memcmp}
@deftypefun {int} {gnutls_memcmp} (const void * @var{s1}, const void * @var{s2}, size_t @var{n})
@var{s1}: the first address to compare

@var{s2}: the second address to compare

@var{n}: the size of memory to compare

This function will operate similarly to @code{memcmp()} , but will operate
on time that depends only on the size of the string. That is will
not return early if the strings don't match on the first byte.

@strong{Returns:} non zero on difference and zero if the buffers are identical.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_memset
@anchor{gnutls_memset}
@deftypefun {void} {gnutls_memset} (void * @var{data}, int @var{c}, size_t @var{size})
@var{data}: the memory to set

@var{c}: the constant byte to fill the memory with

@var{size}: the size of memory

This function will operate similarly to @code{memset()} , but will
not be optimized out by the compiler.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_ocsp_status_request_enable_client
@anchor{gnutls_ocsp_status_request_enable_client}
@deftypefun {int} {gnutls_ocsp_status_request_enable_client} (gnutls_session_t @var{session}, gnutls_datum_t * @var{responder_id}, size_t @var{responder_id_size}, gnutls_datum_t * @var{extensions})
@var{session}: is a @code{gnutls_session_t}  type.

@var{responder_id}: ignored, must be @code{NULL} 

@var{responder_id_size}: ignored, must be zero

@var{extensions}: ignored, must be @code{NULL} 

This function is to be used by clients to request OCSP response
from the server, using the "status_request" TLS extension.  Only
OCSP status type is supported.

Previous versions of GnuTLS supported setting  @code{responder_id} and
 @code{extensions} fields, but due to the difficult semantics of the
parameter usage, and other issues, this support was removed
since 3.6.0 and these parameters must be set to @code{NULL} .

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

@strong{Since:} 3.1.3
@end deftypefun

@subheading gnutls_ocsp_status_request_get
@anchor{gnutls_ocsp_status_request_get}
@deftypefun {int} {gnutls_ocsp_status_request_get} (gnutls_session_t @var{session}, gnutls_datum_t * @var{response})
@var{session}: is a @code{gnutls_session_t}  type.

@var{response}: a @code{gnutls_datum_t}  with DER encoded OCSP response

This function returns the OCSP status response received
from the TLS server. The  @code{response} should be treated as
constant. If no OCSP response is available then
@code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE}  is returned.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

@strong{Since:} 3.1.3
@end deftypefun

@subheading gnutls_ocsp_status_request_get2
@anchor{gnutls_ocsp_status_request_get2}
@deftypefun {int} {gnutls_ocsp_status_request_get2} (gnutls_session_t @var{session}, unsigned @var{idx}, gnutls_datum_t * @var{response})
@var{session}: is a @code{gnutls_session_t}  type.

@var{idx}: the index of peer's certificate

@var{response}: a @code{gnutls_datum_t}  with DER encoded OCSP response

This function returns the OCSP status response received
from the TLS server for the certificate index provided.
The index corresponds to certificates as returned by
gnutls_certificate_get_peers. When index is zero this
function operates identically to @code{gnutls_ocsp_status_request_get()} .

The returned  @code{response} should be treated as
constant. If no OCSP response is available for the
given index then @code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE} 
is returned.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_ocsp_status_request_is_checked
@anchor{gnutls_ocsp_status_request_is_checked}
@deftypefun {unsigned} {gnutls_ocsp_status_request_is_checked} (gnutls_session_t @var{session}, unsigned int @var{flags})
@var{session}: is a gnutls session

@var{flags}: should be zero or @code{GNUTLS_OCSP_SR_IS_AVAIL} 

When flags are zero this function returns non-zero if a valid OCSP status
response was included in the TLS handshake. That is, an OCSP status response
which is not too old, superseded or marks the certificate as revoked.
It returns zero otherwise.

When the flag @code{GNUTLS_OCSP_SR_IS_AVAIL}  is specified, the function
returns non-zero if an OCSP status response was included in the handshake
even if it was invalid. Otherwise, if no OCSP status response was included,
it returns zero. The @code{GNUTLS_OCSP_SR_IS_AVAIL}  flag was introduced in GnuTLS 3.4.0.

This is a helper function when needing to decide whether to perform an
explicit OCSP validity check on the peer's certificate. Should be called after
any of gnutls_certificate_verify_peers*() are called.

This function is always usable on client side, but on server side only
under TLS 1.3, which is the first version of TLS that allows cliend-side OCSP
responses.

@strong{Returns:} Non-zero if the response was valid, or a zero if it wasn't sent,
or sent and was invalid.

@strong{Since:} 3.1.4
@end deftypefun

@subheading gnutls_oid_to_digest
@anchor{gnutls_oid_to_digest}
@deftypefun {gnutls_digest_algorithm_t} {gnutls_oid_to_digest} (const char * @var{oid})
@var{oid}: is an object identifier

Converts a textual object identifier to a @code{gnutls_digest_algorithm_t}  value.

@strong{Returns:} a @code{gnutls_digest_algorithm_t}  id of the specified digest
algorithm, or @code{GNUTLS_DIG_UNKNOWN}  on failure.

@strong{Since:} 3.4.3
@end deftypefun

@subheading gnutls_oid_to_ecc_curve
@anchor{gnutls_oid_to_ecc_curve}
@deftypefun {gnutls_ecc_curve_t} {gnutls_oid_to_ecc_curve} (const char * @var{oid})
@var{oid}: is a curve's OID


@strong{Returns:} return a @code{gnutls_ecc_curve_t}  value corresponding to
the specified OID, or @code{GNUTLS_ECC_CURVE_INVALID}  on error.

@strong{Since:} 3.4.3
@end deftypefun

@subheading gnutls_oid_to_gost_paramset
@anchor{gnutls_oid_to_gost_paramset}
@deftypefun {gnutls_gost_paramset_t} {gnutls_oid_to_gost_paramset} (const char * @var{oid})
@var{oid}: is an object identifier

Converts a textual object identifier to a @code{gnutls_gost_paramset_t}  value.

@strong{Returns:} a @code{gnutls_gost_paramset_get_oid}  of the specified GOST 28147
param st, or @code{GNUTLS_GOST_PARAMSET_UNKNOWN}  on failure.

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_oid_to_mac
@anchor{gnutls_oid_to_mac}
@deftypefun {gnutls_mac_algorithm_t} {gnutls_oid_to_mac} (const char * @var{oid})
@var{oid}: is an object identifier

Converts a textual object identifier typically from PKCS@code{5}  values to a @code{gnutls_mac_algorithm_t}  value.

@strong{Returns:} a @code{gnutls_mac_algorithm_t}  id of the specified digest
algorithm, or @code{GNUTLS_MAC_UNKNOWN}  on failure.

@strong{Since:} 3.5.4
@end deftypefun

@subheading gnutls_oid_to_pk
@anchor{gnutls_oid_to_pk}
@deftypefun {gnutls_pk_algorithm_t} {gnutls_oid_to_pk} (const char * @var{oid})
@var{oid}: is an object identifier

Converts a textual object identifier to a @code{gnutls_pk_algorithm_t}  value.

@strong{Returns:} a @code{gnutls_pk_algorithm_t}  id of the specified digest
algorithm, or @code{GNUTLS_PK_UNKNOWN}  on failure.

@strong{Since:} 3.4.3
@end deftypefun

@subheading gnutls_oid_to_sign
@anchor{gnutls_oid_to_sign}
@deftypefun {gnutls_sign_algorithm_t} {gnutls_oid_to_sign} (const char * @var{oid})
@var{oid}: is an object identifier

Converts a textual object identifier to a @code{gnutls_sign_algorithm_t}  value.

@strong{Returns:} a @code{gnutls_sign_algorithm_t}  id of the specified digest
algorithm, or @code{GNUTLS_SIGN_UNKNOWN}  on failure.

@strong{Since:} 3.4.3
@end deftypefun

@subheading gnutls_openpgp_send_cert
@anchor{gnutls_openpgp_send_cert}
@deftypefun {void} {gnutls_openpgp_send_cert} (gnutls_session_t @var{session}, gnutls_openpgp_crt_status_t @var{status})
@var{session}: is a gnutls session

@var{status}: is ignored

This function is no-op.

@strong{Returns:} @code{GNUTLS_E_UNIMPLEMENTED_FEATURE} .
@end deftypefun

@subheading gnutls_packet_deinit
@anchor{gnutls_packet_deinit}
@deftypefun {void} {gnutls_packet_deinit} (gnutls_packet_t @var{packet})
@var{packet}: is a pointer to a @code{gnutls_packet_st}  structure.

This function will deinitialize all data associated with
the received packet.

@strong{Since:} 3.3.5
@end deftypefun

@subheading gnutls_packet_get
@anchor{gnutls_packet_get}
@deftypefun {void} {gnutls_packet_get} (gnutls_packet_t @var{packet}, gnutls_datum_t * @var{data}, unsigned char * @var{sequence})
@var{packet}: is a @code{gnutls_packet_t}  type.

@var{data}: will contain the data present in the  @code{packet} structure (may be @code{NULL} )

@var{sequence}: the 8-bytes of the packet sequence number (may be @code{NULL} )

This function returns the data and sequence number associated with
the received packet.

@strong{Since:} 3.3.5
@end deftypefun

@subheading gnutls_pem_base64_decode
@anchor{gnutls_pem_base64_decode}
@deftypefun {int} {gnutls_pem_base64_decode} (const char * @var{header}, const gnutls_datum_t * @var{b64_data}, unsigned char * @var{result}, size_t * @var{result_size})
@var{header}: A null terminated string with the PEM header (eg. CERTIFICATE)

@var{b64_data}: contain the encoded data

@var{result}: the place where decoded data will be copied

@var{result_size}: holds the size of the result

This function will decode the given encoded data.  If the header
given is non @code{NULL}  this function will search for "-----BEGIN header"
and decode only this part.  Otherwise it will decode the first PEM
packet found.

@strong{Returns:} On success @code{GNUTLS_E_SUCCESS}  (0) is returned,
@code{GNUTLS_E_SHORT_MEMORY_BUFFER}  is returned if the buffer given is
not long enough, or 0 on success.
@end deftypefun

@subheading gnutls_pem_base64_decode2
@anchor{gnutls_pem_base64_decode2}
@deftypefun {int} {gnutls_pem_base64_decode2} (const char * @var{header}, const gnutls_datum_t * @var{b64_data}, gnutls_datum_t * @var{result})
@var{header}: The PEM header (eg. CERTIFICATE)

@var{b64_data}: contains the encoded data

@var{result}: the location of decoded data

This function will decode the given encoded data. The decoded data
will be allocated, and stored into result.  If the header given is
non null this function will search for "-----BEGIN header" and
decode only this part. Otherwise it will decode the first PEM
packet found.

You should use @code{gnutls_free()}  to free the returned data.

Note, that prior to GnuTLS 3.4.0 this function was available
under the name @code{gnutls_pem_base64_decode_alloc()} . There is
compatibility macro pointing to this function.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_pem_base64_encode
@anchor{gnutls_pem_base64_encode}
@deftypefun {int} {gnutls_pem_base64_encode} (const char * @var{msg}, const gnutls_datum_t * @var{data}, char * @var{result}, size_t * @var{result_size})
@var{msg}: is a message to be put in the header (may be @code{NULL} )

@var{data}: contain the raw data

@var{result}: the place where base64 data will be copied

@var{result_size}: holds the size of the result

This function will convert the given data to printable data, using
the base64 encoding. This is the encoding used in PEM messages.

The output string will be null terminated, although the output size will
not include the terminating null.

@strong{Returns:} On success @code{GNUTLS_E_SUCCESS}  (0) is returned,
@code{GNUTLS_E_SHORT_MEMORY_BUFFER}  is returned if the buffer given is
not long enough, or 0 on success.
@end deftypefun

@subheading gnutls_pem_base64_encode2
@anchor{gnutls_pem_base64_encode2}
@deftypefun {int} {gnutls_pem_base64_encode2} (const char * @var{header}, const gnutls_datum_t * @var{data}, gnutls_datum_t * @var{result})
@var{header}: is a message to be put in the encoded header (may be @code{NULL} )

@var{data}: contains the raw data

@var{result}: will hold the newly allocated encoded data

This function will convert the given data to printable data, using
the base64 encoding.  This is the encoding used in PEM messages.
This function will allocate the required memory to hold the encoded
data.

You should use @code{gnutls_free()}  to free the returned data.

Note, that prior to GnuTLS 3.4.0 this function was available
under the name @code{gnutls_pem_base64_encode_alloc()} . There is
compatibility macro pointing to this function.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_perror
@anchor{gnutls_perror}
@deftypefun {void} {gnutls_perror} (int @var{error})
@var{error}: is a GnuTLS error code, a negative error code

This function is like @code{perror()} . The only difference is that it
accepts an error number returned by a gnutls function.
@end deftypefun

@subheading gnutls_pk_algorithm_get_name
@anchor{gnutls_pk_algorithm_get_name}
@deftypefun {const char *} {gnutls_pk_algorithm_get_name} (gnutls_pk_algorithm_t @var{algorithm})
@var{algorithm}: is a pk algorithm

Convert a @code{gnutls_pk_algorithm_t}  value to a string.

@strong{Returns:} a string that contains the name of the specified public
key algorithm, or @code{NULL} .
@end deftypefun

@subheading gnutls_pk_bits_to_sec_param
@anchor{gnutls_pk_bits_to_sec_param}
@deftypefun {gnutls_sec_param_t} {gnutls_pk_bits_to_sec_param} (gnutls_pk_algorithm_t @var{algo}, unsigned int @var{bits})
@var{algo}: is a public key algorithm

@var{bits}: is the number of bits

This is the inverse of @code{gnutls_sec_param_to_pk_bits()} . Given an algorithm
and the number of bits, it will return the security parameter. This is
a rough indication.

@strong{Returns:} The security parameter.

@strong{Since:} 2.12.0
@end deftypefun

@subheading gnutls_pk_get_id
@anchor{gnutls_pk_get_id}
@deftypefun {gnutls_pk_algorithm_t} {gnutls_pk_get_id} (const char * @var{name})
@var{name}: is a string containing a public key algorithm name.

Convert a string to a @code{gnutls_pk_algorithm_t}  value.  The names are
compared in a case insensitive way.  For example,
gnutls_pk_get_id("RSA") will return @code{GNUTLS_PK_RSA} .

@strong{Returns:} a @code{gnutls_pk_algorithm_t}  id of the specified public key
algorithm string, or @code{GNUTLS_PK_UNKNOWN}  on failures.

@strong{Since:} 2.6.0
@end deftypefun

@subheading gnutls_pk_get_name
@anchor{gnutls_pk_get_name}
@deftypefun {const char *} {gnutls_pk_get_name} (gnutls_pk_algorithm_t @var{algorithm})
@var{algorithm}: is a public key algorithm

Convert a @code{gnutls_pk_algorithm_t}  value to a string.

@strong{Returns:} a pointer to a string that contains the name of the
specified public key algorithm, or @code{NULL} .

@strong{Since:} 2.6.0
@end deftypefun

@subheading gnutls_pk_get_oid
@anchor{gnutls_pk_get_oid}
@deftypefun {const char *} {gnutls_pk_get_oid} (gnutls_pk_algorithm_t @var{algorithm})
@var{algorithm}: is a public key algorithm

Convert a @code{gnutls_pk_algorithm_t}  value to its object identifier string.

@strong{Returns:} a pointer to a string that contains the object identifier of the
specified public key algorithm, or @code{NULL} .

@strong{Since:} 3.4.3
@end deftypefun

@subheading gnutls_pk_list
@anchor{gnutls_pk_list}
@deftypefun {const gnutls_pk_algorithm_t *} {gnutls_pk_list} ( @var{void})

Get a list of supported public key algorithms.

This function is not thread safe.

@strong{Returns:} a (0)-terminated list of @code{gnutls_pk_algorithm_t}  integers
indicating the available ciphers.

@strong{Since:} 2.6.0
@end deftypefun

@subheading gnutls_pk_to_sign
@anchor{gnutls_pk_to_sign}
@deftypefun {gnutls_sign_algorithm_t} {gnutls_pk_to_sign} (gnutls_pk_algorithm_t @var{pk}, gnutls_digest_algorithm_t @var{hash})
@var{pk}: is a public key algorithm

@var{hash}: a hash algorithm

This function maps public key and hash algorithms combinations
to signature algorithms.

@strong{Returns:} return a @code{gnutls_sign_algorithm_t}  value, or @code{GNUTLS_SIGN_UNKNOWN}  on error.
@end deftypefun

@subheading gnutls_prf
@anchor{gnutls_prf}
@deftypefun {int} {gnutls_prf} (gnutls_session_t @var{session}, size_t @var{label_size}, const char * @var{label}, int @var{server_random_first}, size_t @var{extra_size}, const char * @var{extra}, size_t @var{outsize}, char * @var{out})
@var{session}: is a @code{gnutls_session_t}  type.

@var{label_size}: length of the  @code{label} variable.

@var{label}: label used in PRF computation, typically a short string.

@var{server_random_first}: non-zero if server random field should be first in seed

@var{extra_size}: length of the  @code{extra} variable.

@var{extra}: optional extra data to seed the PRF with.

@var{outsize}: size of pre-allocated output buffer to hold the output.

@var{out}: pre-allocated buffer to hold the generated data.

Applies the TLS Pseudo-Random-Function (PRF) on the master secret
and the provided data, seeded with the client and server random fields.
For the key expansion specified in RFC5705 see @code{gnutls_prf_rfc5705()} .

The  @code{label} variable usually contains a string denoting the purpose
for the generated data.  The  @code{server_random_first} indicates whether
the client random field or the server random field should be first
in the seed.  Non-zero indicates that the server random field is first,
0 that the client random field is first.

The  @code{extra} variable can be used to add more data to the seed, after
the random variables.  It can be used to make sure the
generated output is strongly connected to some additional data
(e.g., a string used in user authentication).

The output is placed in  @code{out} , which must be pre-allocated.

@strong{Note:} This function produces identical output with @code{gnutls_prf_rfc5705()} 
when  @code{server_random_first} is set to 0 and  @code{extra} is @code{NULL} . Under TLS1.3
this function will only operate when these conditions are true, or otherwise
return @code{GNUTLS_E_INVALID_REQUEST} .

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.
@end deftypefun

@subheading gnutls_prf_early
@anchor{gnutls_prf_early}
@deftypefun {int} {gnutls_prf_early} (gnutls_session_t @var{session}, size_t @var{label_size}, const char * @var{label}, size_t @var{context_size}, const char * @var{context}, size_t @var{outsize}, char * @var{out})
@var{session}: is a @code{gnutls_session_t}  type.

@var{label_size}: length of the  @code{label} variable.

@var{label}: label used in PRF computation, typically a short string.

@var{context_size}: length of the  @code{extra} variable.

@var{context}: optional extra data to seed the PRF with.

@var{outsize}: size of pre-allocated output buffer to hold the output.

@var{out}: pre-allocated buffer to hold the generated data.

This function is similar to @code{gnutls_prf_rfc5705()} , but only works in
TLS 1.3 or later to export early keying material.

Note that the keying material is only available after the
ClientHello message is processed and before the application traffic
keys are established.  Therefore this function shall be called in a
handshake hook function for @code{GNUTLS_HANDSHAKE_CLIENT_HELLO} .

The  @code{label} variable usually contains a string denoting the purpose
for the generated data.

The  @code{context} variable can be used to add more data to the seed, after
the random variables.  It can be used to make sure the
generated output is strongly connected to some additional data
(e.g., a string used in user authentication).

The output is placed in  @code{out} , which must be pre-allocated.

Note that, to provide the RFC5705 context, the  @code{context} variable
must be non-null.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.

@strong{Since:} 3.6.8
@end deftypefun

@subheading gnutls_prf_hash_get
@anchor{gnutls_prf_hash_get}
@deftypefun {gnutls_digest_algorithm_t} {gnutls_prf_hash_get} (const gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get the currently used hash algorithm. In TLS 1.3, the hash
algorithm is used for both the key derivation function and
handshake message authentication code. In TLS 1.2, it matches the
hash algorithm used for PRF.

@strong{Returns:} the currently used hash algorithm, a
@code{gnutls_digest_algorithm_t}  value.

@strong{Since:} 3.6.13
@end deftypefun

@subheading gnutls_prf_raw
@anchor{gnutls_prf_raw}
@deftypefun {int} {gnutls_prf_raw} (gnutls_session_t @var{session}, size_t @var{label_size}, const char * @var{label}, size_t @var{seed_size}, const char * @var{seed}, size_t @var{outsize}, char * @var{out})
@var{session}: is a @code{gnutls_session_t}  type.

@var{label_size}: length of the  @code{label} variable.

@var{label}: label used in PRF computation, typically a short string.

@var{seed_size}: length of the  @code{seed} variable.

@var{seed}: optional extra data to seed the PRF with.

@var{outsize}: size of pre-allocated output buffer to hold the output.

@var{out}: pre-allocated buffer to hold the generated data.

Apply the TLS Pseudo-Random-Function (PRF) on the master secret
and the provided data.

The  @code{label} variable usually contains a string denoting the purpose
for the generated data.  The  @code{seed} usually contains data such as the
client and server random, perhaps together with some additional
data that is added to guarantee uniqueness of the output for a
particular purpose.

Because the output is not guaranteed to be unique for a particular
session unless  @code{seed} includes the client random and server random
fields (the PRF would output the same data on another connection
resumed from the first one), it is not recommended to use this
function directly.  The @code{gnutls_prf()}  function seeds the PRF with the
client and server random fields directly, and is recommended if you
want to generate pseudo random data unique for each session.

@strong{Note:} This function will only operate under TLS versions prior to 1.3.
In TLS1.3 the use of PRF is replaced with HKDF and the generic
exporters like @code{gnutls_prf_rfc5705()}  should be used instead. Under
TLS1.3 this function returns @code{GNUTLS_E_INVALID_REQUEST} .

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.
@end deftypefun

@subheading gnutls_prf_rfc5705
@anchor{gnutls_prf_rfc5705}
@deftypefun {int} {gnutls_prf_rfc5705} (gnutls_session_t @var{session}, size_t @var{label_size}, const char * @var{label}, size_t @var{context_size}, const char * @var{context}, size_t @var{outsize}, char * @var{out})
@var{session}: is a @code{gnutls_session_t}  type.

@var{label_size}: length of the  @code{label} variable.

@var{label}: label used in PRF computation, typically a short string.

@var{context_size}: length of the  @code{extra} variable.

@var{context}: optional extra data to seed the PRF with.

@var{outsize}: size of pre-allocated output buffer to hold the output.

@var{out}: pre-allocated buffer to hold the generated data.

Exports keying material from TLS/DTLS session to an application, as
specified in RFC5705.

In the TLS versions prior to 1.3, it applies the TLS
Pseudo-Random-Function (PRF) on the master secret and the provided
data, seeded with the client and server random fields.

In TLS 1.3, it applies HKDF on the exporter master secret derived
from the master secret.

The  @code{label} variable usually contains a string denoting the purpose
for the generated data.

The  @code{context} variable can be used to add more data to the seed, after
the random variables.  It can be used to make sure the
generated output is strongly connected to some additional data
(e.g., a string used in user authentication). 

The output is placed in  @code{out} , which must be pre-allocated.

Note that, to provide the RFC5705 context, the  @code{context} variable
must be non-null.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.

@strong{Since:} 3.4.4
@end deftypefun

@subheading gnutls_priority_certificate_type_list
@anchor{gnutls_priority_certificate_type_list}
@deftypefun {int} {gnutls_priority_certificate_type_list} (gnutls_priority_t @var{pcache}, const unsigned int ** @var{list})
@var{pcache}: is a @code{gnutls_priority_t}  type.

@var{list}: will point to an integer list

Get a list of available certificate types in the priority
structure.

As of version 3.6.4 this function is an alias for
gnutls_priority_certificate_type_list2 with the target parameter
set to:
- GNUTLS_CTYPE_SERVER, if the @code{SERVER_PRECEDENCE}  option is set
- GNUTLS_CTYPE_CLIENT, otherwise.

@strong{Returns:} the number of certificate types, or an error code.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_priority_certificate_type_list2
@anchor{gnutls_priority_certificate_type_list2}
@deftypefun {int} {gnutls_priority_certificate_type_list2} (gnutls_priority_t @var{pcache}, const unsigned int ** @var{list}, gnutls_ctype_target_t @var{target})
@var{pcache}: is a @code{gnutls_priority_t}  type.

@var{list}: will point to an integer list.

@var{target}: is a @code{gnutls_ctype_target_t}  type. Valid arguments are
GNUTLS_CTYPE_CLIENT and GNUTLS_CTYPE_SERVER

Get a list of available certificate types for the given target
in the priority structure.

@strong{Returns:} the number of certificate types, or an error code.

@strong{Since:} 3.6.4
@end deftypefun

@subheading gnutls_priority_cipher_list
@anchor{gnutls_priority_cipher_list}
@deftypefun {int} {gnutls_priority_cipher_list} (gnutls_priority_t @var{pcache}, const unsigned int ** @var{list})
@var{pcache}: is a @code{gnutls_priority_t}  type.

@var{list}: will point to an integer list

Get a list of available ciphers in the priority
structure.

@strong{Returns:} the number of items, or an error code.

@strong{Since:} 3.2.3
@end deftypefun

@subheading gnutls_priority_deinit
@anchor{gnutls_priority_deinit}
@deftypefun {void} {gnutls_priority_deinit} (gnutls_priority_t @var{priority_cache})
@var{priority_cache}: is a @code{gnutls_priority_t}  type.

Deinitializes the priority cache.
@end deftypefun

@subheading gnutls_priority_ecc_curve_list
@anchor{gnutls_priority_ecc_curve_list}
@deftypefun {int} {gnutls_priority_ecc_curve_list} (gnutls_priority_t @var{pcache}, const unsigned int ** @var{list})
@var{pcache}: is a @code{gnutls_priority_t}  type.

@var{list}: will point to an integer list

Get a list of available elliptic curves in the priority
structure.

@strong{Deprecated:} This function has been replaced by
@code{gnutls_priority_group_list()}  since 3.6.0.

@strong{Returns:} the number of items, or an error code.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_priority_get_cipher_suite_index
@anchor{gnutls_priority_get_cipher_suite_index}
@deftypefun {int} {gnutls_priority_get_cipher_suite_index} (gnutls_priority_t @var{pcache}, unsigned int @var{idx}, unsigned int * @var{sidx})
@var{pcache}: is a @code{gnutls_priority_t}  type.

@var{idx}: is an index number.

@var{sidx}: internal index of cipher suite to get information about.

Provides the internal ciphersuite index to be used with
@code{gnutls_cipher_suite_info()} . The index  @code{idx} provided is an
index kept at the priorities structure. It might be that a valid
priorities index does not correspond to a ciphersuite and in
that case @code{GNUTLS_E_UNKNOWN_CIPHER_SUITE}  will be returned.
Once the last available index is crossed then
@code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE}  will be returned.

@strong{Returns:} On success it returns @code{GNUTLS_E_SUCCESS}  (0), or a negative error value otherwise.

@strong{Since:} 3.0.9
@end deftypefun

@subheading gnutls_priority_group_list
@anchor{gnutls_priority_group_list}
@deftypefun {int} {gnutls_priority_group_list} (gnutls_priority_t @var{pcache}, const unsigned int ** @var{list})
@var{pcache}: is a @code{gnutls_priority_t}  type.

@var{list}: will point to an integer list

Get a list of available groups in the priority
structure.

@strong{Returns:} the number of items, or an error code.

@strong{Since:} 3.6.0
@end deftypefun

@subheading gnutls_priority_init
@anchor{gnutls_priority_init}
@deftypefun {int} {gnutls_priority_init} (gnutls_priority_t * @var{priority_cache}, const char * @var{priorities}, const char ** @var{err_pos})
@var{priority_cache}: is a @code{gnutls_priority_t}  type.

@var{priorities}: is a string describing priorities (may be @code{NULL} )

@var{err_pos}: In case of an error this will have the position in the string the error occurred

For applications that do not modify their crypto settings per release, consider
using @code{gnutls_priority_init2()}  with @code{GNUTLS_PRIORITY_INIT_DEF_APPEND}  flag
instead. We suggest to use centralized crypto settings handled by the GnuTLS
library, and applications modifying the default settings to their needs.

This function is identical to @code{gnutls_priority_init2()}  with zero
flags.

A @code{NULL}   @code{priorities} string indicates the default priorities to be
used (this is available since GnuTLS 3.3.0).

@strong{Returns:} On syntax error @code{GNUTLS_E_INVALID_REQUEST}  is returned,
@code{GNUTLS_E_SUCCESS}  on success, or an error code.
@end deftypefun

@subheading gnutls_priority_init2
@anchor{gnutls_priority_init2}
@deftypefun {int} {gnutls_priority_init2} (gnutls_priority_t * @var{priority_cache}, const char * @var{priorities}, const char ** @var{err_pos}, unsigned @var{flags})
@var{priority_cache}: is a @code{gnutls_priority_t}  type.

@var{priorities}: is a string describing priorities (may be @code{NULL} )

@var{err_pos}: In case of an error this will have the position in the string the error occurred

@var{flags}: zero or @code{GNUTLS_PRIORITY_INIT_DEF_APPEND} 

Sets priorities for the ciphers, key exchange methods, and macs.
The  @code{priority_cache} should be deinitialized
using @code{gnutls_priority_deinit()} .

The @code{priorities}  option allows you to specify a colon
separated list of the cipher priorities to enable.
Some keywords are defined to provide quick access
to common preferences.

When  @code{flags} is set to @code{GNUTLS_PRIORITY_INIT_DEF_APPEND}  then the  @code{priorities} specified will be appended to the default options.

Unless there is a special need, use the "NORMAL" keyword to
apply a reasonable security level, or "NORMAL:%COMPAT" for compatibility.

"PERFORMANCE" means all the "secure" ciphersuites are enabled,
limited to 128 bit ciphers and sorted by terms of speed
performance.

"LEGACY" the NORMAL settings for GnuTLS 3.2.x or earlier. There is
no verification profile set, and the allowed DH primes are considered
weak today.

"NORMAL" means all "secure" ciphersuites. The 256-bit ciphers are
included as a fallback only.  The ciphers are sorted by security
margin.

"PFS" means all "secure" ciphersuites that support perfect forward secrecy.
The 256-bit ciphers are included as a fallback only.
The ciphers are sorted by security margin.

"SECURE128" means all "secure" ciphersuites of security level 128-bit
or more.

"SECURE192" means all "secure" ciphersuites of security level 192-bit
or more.

"SUITEB128" means all the NSA SuiteB ciphersuites with security level
of 128.

"SUITEB192" means all the NSA SuiteB ciphersuites with security level
of 192.

"NONE" means nothing is enabled.  This disables everything, including protocols.

"@@KEYWORD1,KEYWORD2,..." The system administrator imposed settings.
The provided keyword(s) will be expanded from a configuration-time
provided file - default is: /etc/gnutls/config.
Any attributes that follow it, will be appended to the expanded
string. If multiple keywords are provided, separated by commas,
then the first keyword that exists in the configuration file
will be used. At least one of the keywords must exist, or this
function will return an error. Typical usage would be to specify
an application specified keyword first, followed by "SYSTEM" as
a default fallback. e.g., " @code{LIBVIRT} ,SYSTEM:!-VERS-SSL3.0" will
first try to find a config file entry matching "LIBVIRT", but if
that does not exist will use the entry for "SYSTEM". If "SYSTEM"
does not exist either, an error will be returned. In all cases,
the SSL3.0 protocol will be disabled. The system priority file
entries should be formatted as "KEYWORD=VALUE", e.g.,
"SYSTEM=NORMAL:+ARCFOUR-128".

Special keywords are "!", "-" and "+".
"!" or "-" appended with an algorithm will remove this algorithm.
"+" appended with an algorithm will add this algorithm.

Check the GnuTLS manual section "Priority strings" for detailed
information.

@strong{Examples:} 
"NONE:+VERS-TLS-ALL:+MAC-ALL:+RSA:+AES-128-CBC:+SIGN-ALL:+COMP-NULL"

"NORMAL:+ARCFOUR-128" means normal ciphers plus ARCFOUR-128.

"SECURE128:-VERS-SSL3.0" means that only secure ciphers are
and enabled, SSL3.0 is disabled.

"NONE:+VERS-TLS-ALL:+AES-128-CBC:+RSA:+SHA1:+COMP-NULL:+SIGN-RSA-SHA1",

"NONE:+VERS-TLS-ALL:+AES-128-CBC:+ECDHE-RSA:+SHA1:+COMP-NULL:+SIGN-RSA-SHA1:+CURVE-SECP256R1",

"SECURE256:+SECURE128",

Note that "NORMAL:%COMPAT" is the most compatible mode.

A @code{NULL}   @code{priorities} string indicates the default priorities to be
used (this is available since GnuTLS 3.3.0).

@strong{Returns:} On syntax error @code{GNUTLS_E_INVALID_REQUEST}  is returned,
@code{GNUTLS_E_SUCCESS}  on success, or an error code.

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_priority_kx_list
@anchor{gnutls_priority_kx_list}
@deftypefun {int} {gnutls_priority_kx_list} (gnutls_priority_t @var{pcache}, const unsigned int ** @var{list})
@var{pcache}: is a @code{gnutls_priority_t}  type.

@var{list}: will point to an integer list

Get a list of available key exchange methods in the priority
structure.

@strong{Returns:} the number of items, or an error code.

@strong{Since:} 3.2.3
@end deftypefun

@subheading gnutls_priority_mac_list
@anchor{gnutls_priority_mac_list}
@deftypefun {int} {gnutls_priority_mac_list} (gnutls_priority_t @var{pcache}, const unsigned int ** @var{list})
@var{pcache}: is a @code{gnutls_priority_t}  type.

@var{list}: will point to an integer list

Get a list of available MAC algorithms in the priority
structure.

@strong{Returns:} the number of items, or an error code.

@strong{Since:} 3.2.3
@end deftypefun

@subheading gnutls_priority_protocol_list
@anchor{gnutls_priority_protocol_list}
@deftypefun {int} {gnutls_priority_protocol_list} (gnutls_priority_t @var{pcache}, const unsigned int ** @var{list})
@var{pcache}: is a @code{gnutls_priority_t}  type.

@var{list}: will point to an integer list

Get a list of available TLS version numbers in the priority
structure.

@strong{Returns:} the number of protocols, or an error code.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_priority_set
@anchor{gnutls_priority_set}
@deftypefun {int} {gnutls_priority_set} (gnutls_session_t @var{session}, gnutls_priority_t @var{priority})
@var{session}: is a @code{gnutls_session_t}  type.

@var{priority}: is a @code{gnutls_priority_t}  type.

Sets the priorities to use on the ciphers, key exchange methods,
and macs. Note that this function is expected to be called once
per session; when called multiple times (e.g., before a re-handshake,
the caller should make sure that any new settings are not incompatible
with the original session).

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code on error.
@end deftypefun

@subheading gnutls_priority_set_direct
@anchor{gnutls_priority_set_direct}
@deftypefun {int} {gnutls_priority_set_direct} (gnutls_session_t @var{session}, const char * @var{priorities}, const char ** @var{err_pos})
@var{session}: is a @code{gnutls_session_t}  type.

@var{priorities}: is a string describing priorities

@var{err_pos}: In case of an error this will have the position in the string the error occurred

Sets the priorities to use on the ciphers, key exchange methods,
and macs.  This function avoids keeping a
priority cache and is used to directly set string priorities to a
TLS session.  For documentation check the @code{gnutls_priority_init()} .

To use a reasonable default, consider using @code{gnutls_set_default_priority()} ,
or @code{gnutls_set_default_priority_append()}  instead of this function.

@strong{Returns:} On syntax error @code{GNUTLS_E_INVALID_REQUEST}  is returned,
@code{GNUTLS_E_SUCCESS}  on success, or an error code.
@end deftypefun

@subheading gnutls_priority_sign_list
@anchor{gnutls_priority_sign_list}
@deftypefun {int} {gnutls_priority_sign_list} (gnutls_priority_t @var{pcache}, const unsigned int ** @var{list})
@var{pcache}: is a @code{gnutls_priority_t}  type.

@var{list}: will point to an integer list

Get a list of available signature algorithms in the priority
structure.

@strong{Returns:} the number of algorithms, or an error code.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_priority_string_list
@anchor{gnutls_priority_string_list}
@deftypefun {const char *} {gnutls_priority_string_list} (unsigned @var{iter}, unsigned int @var{flags})
@var{iter}: an integer counter starting from zero

@var{flags}: one of @code{GNUTLS_PRIORITY_LIST_INIT_KEYWORDS} , @code{GNUTLS_PRIORITY_LIST_SPECIAL} 

Can be used to iterate all available priority strings.
Due to internal implementation details, there are cases where this
function can return the empty string. In that case that string should be ignored.
When no strings are available it returns @code{NULL} .

@strong{Returns:} a priority string

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_protocol_get_id
@anchor{gnutls_protocol_get_id}
@deftypefun {gnutls_protocol_t} {gnutls_protocol_get_id} (const char * @var{name})
@var{name}: is a protocol name

The names are compared in a case insensitive way.

@strong{Returns:} an id of the specified protocol, or
@code{GNUTLS_VERSION_UNKNOWN}  on error.
@end deftypefun

@subheading gnutls_protocol_get_name
@anchor{gnutls_protocol_get_name}
@deftypefun {const char *} {gnutls_protocol_get_name} (gnutls_protocol_t @var{version})
@var{version}: is a (gnutls) version number

Convert a @code{gnutls_protocol_t}  value to a string.

@strong{Returns:} a string that contains the name of the specified TLS
version (e.g., "TLS1.0"), or @code{NULL} .
@end deftypefun

@subheading gnutls_protocol_get_version
@anchor{gnutls_protocol_get_version}
@deftypefun {gnutls_protocol_t} {gnutls_protocol_get_version} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get TLS version, a @code{gnutls_protocol_t}  value.

@strong{Returns:} The version of the currently used protocol.
@end deftypefun

@subheading gnutls_protocol_list
@anchor{gnutls_protocol_list}
@deftypefun {const gnutls_protocol_t *} {gnutls_protocol_list} ( @var{void})

Get a list of supported protocols, e.g. SSL 3.0, TLS 1.0 etc.

This function is not thread safe.

@strong{Returns:} a (0)-terminated list of @code{gnutls_protocol_t}  integers
indicating the available protocols.
@end deftypefun

@subheading gnutls_protocol_set_enabled
@anchor{gnutls_protocol_set_enabled}
@deftypefun {int} {gnutls_protocol_set_enabled} (gnutls_protocol_t @var{version}, unsigned int @var{enabled})
@var{version}: is a (gnutls) version number

@var{enabled}: whether to enable the protocol

Control the previous system-wide setting that marked  @code{version} as
enabled or disabled.  Calling this fuction is allowed
only if allowlisting mode is set in the configuration file,
and only if the system-wide TLS priority string
has not been initialized yet.
The intended usage is to provide applications with a way
to expressly deviate from the distribution or site defaults
inherited from the configuration file.
The modification is composable with further modifications
performed through the priority string mechanism.

This function is not thread-safe and is intended to be called
in the main thread at the beginning of the process execution.

@strong{Returns:} 0 on success or negative error code otherwise.

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_psk_allocate_client_credentials
@anchor{gnutls_psk_allocate_client_credentials}
@deftypefun {int} {gnutls_psk_allocate_client_credentials} (gnutls_psk_client_credentials_t *            @var{sc})
@var{sc}: is a pointer to a @code{gnutls_psk_server_credentials_t}  type.

Allocate a gnutls_psk_client_credentials_t structure.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_psk_allocate_server_credentials
@anchor{gnutls_psk_allocate_server_credentials}
@deftypefun {int} {gnutls_psk_allocate_server_credentials} (gnutls_psk_server_credentials_t *            @var{sc})
@var{sc}: is a pointer to a @code{gnutls_psk_server_credentials_t}  type.

Allocate a gnutls_psk_server_credentials_t structure.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_psk_client_get_hint
@anchor{gnutls_psk_client_get_hint}
@deftypefun {const char *} {gnutls_psk_client_get_hint} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

The PSK identity hint may give the client help in deciding which
username to use.  This should only be called in case of PSK
authentication and in case of a client.

@strong{Note:} there is no hint in TLS 1.3, so this function will return @code{NULL} 
if TLS 1.3 has been negotiated.

@strong{Returns:} the identity hint of the peer, or @code{NULL}  in case of an error or if TLS 1.3 is being used.

@strong{Since:} 2.4.0
@end deftypefun

@subheading gnutls_psk_free_client_credentials
@anchor{gnutls_psk_free_client_credentials}
@deftypefun {void} {gnutls_psk_free_client_credentials} (gnutls_psk_client_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_psk_client_credentials_t}  type.

Free a gnutls_psk_client_credentials_t structure.
@end deftypefun

@subheading gnutls_psk_free_server_credentials
@anchor{gnutls_psk_free_server_credentials}
@deftypefun {void} {gnutls_psk_free_server_credentials} (gnutls_psk_server_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_psk_server_credentials_t}  type.

Free a gnutls_psk_server_credentials_t structure.
@end deftypefun

@subheading gnutls_psk_server_get_username
@anchor{gnutls_psk_server_get_username}
@deftypefun {const char *} {gnutls_psk_server_get_username} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

This should only be called in case of PSK authentication and in
case of a server.

The returned pointer should be considered constant (do not free) and valid 
for the lifetime of the session.

This function will return @code{NULL}  if the username has embedded NULL bytes.
In that case, @code{gnutls_psk_server_get_username2()}  should be used to retrieve the username.

@strong{Returns:} the username of the peer, or @code{NULL}  in case of an error,
or if the username has embedded NULLs.
@end deftypefun

@subheading gnutls_psk_server_get_username2
@anchor{gnutls_psk_server_get_username2}
@deftypefun {int} {gnutls_psk_server_get_username2} (gnutls_session_t @var{session}, gnutls_datum_t * @var{username})
@var{session}: is a gnutls session

@var{username}: a datum that will be filled in by this function

Return a pointer to the username of the peer in the supplied datum. Does not
need to be null-terminated.

This should only be called in case of PSK authentication and in
case of a server.

The returned pointer should be considered constant (do not free) and valid 
for the lifetime of the session.

@strong{Returns:} @code{GNUTLS_E_SUCCESS} , or a negative value in case of an error.
@end deftypefun

@subheading gnutls_psk_set_client_credentials
@anchor{gnutls_psk_set_client_credentials}
@deftypefun {int} {gnutls_psk_set_client_credentials} (gnutls_psk_client_credentials_t @var{res}, const char * @var{username}, const gnutls_datum_t * @var{key}, gnutls_psk_key_flags @var{flags})
@var{res}: is a @code{gnutls_psk_client_credentials_t}  type.

@var{username}: is the user's zero-terminated userid

@var{key}: is the user's key

@var{flags}: indicate the format of the key, either
@code{GNUTLS_PSK_KEY_RAW}  or @code{GNUTLS_PSK_KEY_HEX} .

This function sets the username and password, in a
gnutls_psk_client_credentials_t type.  Those will be used in
PSK authentication.   @code{username} should be an ASCII string or UTF-8
string. In case of a UTF-8 string it is recommended to be following
the PRECIS framework for usernames (rfc8265). The key can be either
in raw byte format or in Hex format (without the 0x prefix).

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_psk_set_client_credentials2
@anchor{gnutls_psk_set_client_credentials2}
@deftypefun {int} {gnutls_psk_set_client_credentials2} (gnutls_psk_client_credentials_t @var{res}, const gnutls_datum_t * @var{username}, const gnutls_datum_t * @var{key}, gnutls_psk_key_flags @var{flags})
@var{res}: is a @code{gnutls_psk_client_credentials_t}  type.

@var{username}: is the userid

@var{key}: is the user's key

@var{flags}: indicate the format of the key, either
@code{GNUTLS_PSK_KEY_RAW}  or @code{GNUTLS_PSK_KEY_HEX} .

This function is identical to @code{gnutls_psk_set_client_credentials()} ,
except that it allows a non-null-terminated username to be introduced.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_psk_set_client_credentials_function
@anchor{gnutls_psk_set_client_credentials_function}
@deftypefun {void} {gnutls_psk_set_client_credentials_function} (gnutls_psk_client_credentials_t         @var{cred}, gnutls_psk_client_credentials_function         * @var{func})
@var{cred}: is a @code{gnutls_psk_server_credentials_t}  type.

@var{func}: is the callback function

This function can be used to set a callback to retrieve the username and
password for client PSK authentication.
The callback's function form is:
int (*callback)(gnutls_session_t, char** username,
gnutls_datum_t* key);

The  @code{username} and  @code{key} ->data must be allocated using @code{gnutls_malloc()} .
The  @code{username} should be an ASCII string or UTF-8
string. In case of a UTF-8 string it is recommended to be following
the PRECIS framework for usernames (rfc8265).

The callback function will be called once per handshake.

The callback function should return 0 on success.
-1 indicates an error.
@end deftypefun

@subheading gnutls_psk_set_client_credentials_function2
@anchor{gnutls_psk_set_client_credentials_function2}
@deftypefun {void} {gnutls_psk_set_client_credentials_function2} (gnutls_psk_client_credentials_t @var{cred}, gnutls_psk_client_credentials_function2 * @var{func})
@var{cred}: is a @code{gnutls_psk_server_credentials_t}  type.

@var{func}: is the callback function

This function can be used to set a callback to retrieve the username and
password for client PSK authentication.
The callback's function form is:
int (*callback)(gnutls_session_t, gnutls_datum_t* username,
gnutls_datum_t* key);

This callback function has the same semantics as that of @code{gnutls_psk_set_client_credentials_function()} ,
but it allows non-string usernames to be used.

The  @code{username} and  @code{key} ->data must be allocated using @code{gnutls_malloc()} .
The  @code{username} should be an ASCII string or UTF-8
string. In case of a UTF-8 string it is recommended to be following
the PRECIS framework for usernames (rfc8265).

The callback function will be called once per handshake.

The callback function should return 0 on success.
-1 indicates an error.
@end deftypefun

@subheading gnutls_psk_set_params_function
@anchor{gnutls_psk_set_params_function}
@deftypefun {void} {gnutls_psk_set_params_function} (gnutls_psk_server_credentials_t @var{res}, gnutls_params_function * @var{func})
@var{res}: is a gnutls_psk_server_credentials_t type

@var{func}: is the function to be called

This function will set a callback in order for the server to get
the Diffie-Hellman or RSA parameters for PSK authentication.  The
callback should return @code{GNUTLS_E_SUCCESS}  (0) on success.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.
@end deftypefun

@subheading gnutls_psk_set_server_credentials_file
@anchor{gnutls_psk_set_server_credentials_file}
@deftypefun {int} {gnutls_psk_set_server_credentials_file} (gnutls_psk_server_credentials_t            @var{res}, const char * @var{password_file})
@var{res}: is a @code{gnutls_psk_server_credentials_t}  type.

@var{password_file}: is the PSK password file (passwd.psk)

This function sets the password file, in a
@code{gnutls_psk_server_credentials_t}  type.  This password file
holds usernames and keys and will be used for PSK authentication.

Each entry in the file consists of a username, followed by a colon
(':') and a hex-encoded key.  If the username contains a colon or
any other special character, it can be hex-encoded preceded by a
'#'.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_psk_set_server_credentials_function
@anchor{gnutls_psk_set_server_credentials_function}
@deftypefun {void} {gnutls_psk_set_server_credentials_function} (gnutls_psk_server_credentials_t         @var{cred}, gnutls_psk_server_credentials_function         * @var{func})
@var{cred}: is a @code{gnutls_psk_server_credentials_t}  type.

@var{func}: is the callback function

This function can be used to set a callback to retrieve the user's PSK credentials.
The callback's function form is:
int (*callback)(gnutls_session_t, const char* username,
gnutls_datum_t* key);

 @code{username} contains the actual username.
The  @code{key} must be filled in using the @code{gnutls_malloc()} .

In case the callback returned a negative number then gnutls will
assume that the username does not exist.

The callback function will only be called once per handshake.  The
callback function should return 0 on success, while -1 indicates
an error.
@end deftypefun

@subheading gnutls_psk_set_server_credentials_function2
@anchor{gnutls_psk_set_server_credentials_function2}
@deftypefun {void} {gnutls_psk_set_server_credentials_function2} (gnutls_psk_server_credentials_t @var{cred}, gnutls_psk_server_credentials_function2 @var{func})
@var{cred}: is a @code{gnutls_psk_server_credentials_t}  type.

@var{func}: is the callback function

This function can be used to set a callback to retrieve the user's PSK credentials.
The callback's function form is:
int (*callback)(gnutls_session_t, const gnutls_datum_t* username,
gnutls_datum_t* key);

This callback function has the same semantics as that of @code{gnutls_psk_set_server_credentials_function()} ,
but it allows non-string usernames to be used.

 @code{username} contains the actual username.
The  @code{key} must be filled in using the @code{gnutls_malloc()} .

In case the callback returned a negative number then gnutls will
assume that the username does not exist.

The callback function will only be called once per handshake.  The
callback function should return 0 on success, while -1 indicates
an error.
@end deftypefun

@subheading gnutls_psk_set_server_credentials_hint
@anchor{gnutls_psk_set_server_credentials_hint}
@deftypefun {int} {gnutls_psk_set_server_credentials_hint} (gnutls_psk_server_credentials_t @var{res}, const char * @var{hint})
@var{res}: is a @code{gnutls_psk_server_credentials_t}  type.

@var{hint}: is the PSK identity hint string

This function sets the identity hint, in a
@code{gnutls_psk_server_credentials_t}  type.  This hint is sent to
the client to help it chose a good PSK credential (i.e., username
and password).

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.

@strong{Since:} 2.4.0
@end deftypefun

@subheading gnutls_psk_set_server_dh_params
@anchor{gnutls_psk_set_server_dh_params}
@deftypefun {void} {gnutls_psk_set_server_dh_params} (gnutls_psk_server_credentials_t @var{res}, gnutls_dh_params_t @var{dh_params})
@var{res}: is a gnutls_psk_server_credentials_t type

@var{dh_params}: is a structure that holds Diffie-Hellman parameters.

This function will set the Diffie-Hellman parameters for an
anonymous server to use. These parameters will be used in
Diffie-Hellman exchange with PSK cipher suites.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.
@end deftypefun

@subheading gnutls_psk_set_server_known_dh_params
@anchor{gnutls_psk_set_server_known_dh_params}
@deftypefun {int} {gnutls_psk_set_server_known_dh_params} (gnutls_psk_server_credentials_t @var{res}, gnutls_sec_param_t @var{sec_param})
@var{res}: is a gnutls_psk_server_credentials_t type

@var{sec_param}: is an option of the @code{gnutls_sec_param_t}  enumeration

This function will set the Diffie-Hellman parameters for a
PSK server to use. These parameters will be used in
Ephemeral Diffie-Hellman cipher suites and will be selected from
the FFDHE set of RFC7919 according to the security level provided.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a
negative error value.

@strong{Since:} 3.5.6
@end deftypefun

@subheading gnutls_psk_set_server_params_function
@anchor{gnutls_psk_set_server_params_function}
@deftypefun {void} {gnutls_psk_set_server_params_function} (gnutls_psk_server_credentials_t @var{res}, gnutls_params_function * @var{func})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type

@var{func}: is the function to be called

This function will set a callback in order for the server to get
the Diffie-Hellman parameters for PSK authentication.  The callback
should return @code{GNUTLS_E_SUCCESS}  (0) on success.

@strong{Deprecated:} This function is unnecessary and discouraged on GnuTLS 3.6.0
or later. Since 3.6.0, DH parameters are negotiated
following RFC7919.
@end deftypefun

@subheading gnutls_random_art
@anchor{gnutls_random_art}
@deftypefun {int} {gnutls_random_art} (gnutls_random_art_t @var{type}, const char * @var{key_type}, unsigned int @var{key_size}, void * @var{fpr}, size_t @var{fpr_size}, gnutls_datum_t * @var{art})
@var{type}: The type of the random art (for now only @code{GNUTLS_RANDOM_ART_OPENSSH}  is supported)

@var{key_type}: The type of the key (RSA, DSA etc.)

@var{key_size}: The size of the key in bits

@var{fpr}: The fingerprint of the key

@var{fpr_size}: The size of the fingerprint

@var{art}: The returned random art

This function will convert a given fingerprint to an "artistic"
image. The returned image is allocated using @code{gnutls_malloc()} , is
null-terminated but art->size will not account the terminating null.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_range_split
@anchor{gnutls_range_split}
@deftypefun {int} {gnutls_range_split} (gnutls_session_t @var{session}, const gnutls_range_st * @var{orig}, gnutls_range_st * @var{next}, gnutls_range_st * @var{remainder})
@var{session}: is a @code{gnutls_session_t}  type

@var{orig}: is the original range provided by the user

@var{next}: is the returned range that can be conveyed in a TLS record

@var{remainder}: is the returned remaining range

This function should be used when it is required to hide the length
of very long data that cannot be directly provided to @code{gnutls_record_send_range()} .
In that case this function should be called with the desired length
hiding range in  @code{orig} . The returned  @code{next} value should then be used in
the next call to @code{gnutls_record_send_range()}  with the partial data.
That process should be repeated until  @code{remainder} is (0,0).

@strong{Returns:} 0 in case splitting succeeds, non zero in case of error.
Note that  @code{orig} is not changed, while the values of  @code{next} and  @code{remainder} are modified to store the resulting values.
@end deftypefun

@subheading gnutls_reauth
@anchor{gnutls_reauth}
@deftypefun {int} {gnutls_reauth} (gnutls_session_t @var{session}, unsigned int @var{flags})
@var{session}: is a @code{gnutls_session_t}  type.

@var{flags}: must be zero

This function performs the post-handshake authentication
for TLS 1.3. The post-handshake authentication is initiated by the server
by calling this function. Clients respond when @code{GNUTLS_E_REAUTH_REQUEST} 
has been seen while receiving data.

The non-fatal errors expected by this function are:
@code{GNUTLS_E_INTERRUPTED} , @code{GNUTLS_E_AGAIN} , as well as
@code{GNUTLS_E_GOT_APPLICATION_DATA}  when called on server side.

The former two interrupt the authentication procedure due to the transport
layer being interrupted, and the latter because there were pending data prior
to peer initiating the re-authentication. The server should read/process that
data as unauthenticated and retry calling @code{gnutls_reauth()} .

When this function is called under TLS1.2 or earlier or the peer didn't
advertise post-handshake auth, it always fails with
@code{GNUTLS_E_INVALID_REQUEST} . The verification of the received peers certificate
is delegated to the session or credentials verification callbacks. A
server can check whether post handshake authentication is supported
by the client by checking the session flags with @code{gnutls_session_get_flags()} .

Prior to calling this function in server side, the function
@code{gnutls_certificate_server_set_request()}  must be called setting expectations
for the received certificate (request or require). If none are set
this function will return with @code{GNUTLS_E_INVALID_REQUEST} .

Note that post handshake authentication is available irrespective
of the initial negotiation type (PSK or certificate). In all cases
however, certificate credentials must be set to the session prior
to calling this function.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on a successful authentication, otherwise a negative error code.
@end deftypefun

@subheading gnutls_record_can_use_length_hiding
@anchor{gnutls_record_can_use_length_hiding}
@deftypefun {unsigned} {gnutls_record_can_use_length_hiding} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

If the session supports length-hiding padding, you can
invoke @code{gnutls_record_send_range()}  to send a message whose
length is hidden in the given range. If the session does not
support length hiding padding, you can use the standard
@code{gnutls_record_send()}  function, or @code{gnutls_record_send_range()} 
making sure that the range is the same as the length of the
message you are trying to send.

@strong{Returns:} true (1) if the current session supports length-hiding
padding, false (0) if the current session does not.
@end deftypefun

@subheading gnutls_record_check_corked
@anchor{gnutls_record_check_corked}
@deftypefun {size_t} {gnutls_record_check_corked} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function checks if there pending corked
data in the gnutls buffers --see @code{gnutls_record_cork()} .

@strong{Returns:} Returns the size of the corked data or zero.

@strong{Since:} 3.2.8
@end deftypefun

@subheading gnutls_record_check_pending
@anchor{gnutls_record_check_pending}
@deftypefun {size_t} {gnutls_record_check_pending} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function checks if there are unread data
in the gnutls buffers. If the return value is
non-zero the next call to @code{gnutls_record_recv()} 
is guaranteed not to block.

@strong{Returns:} Returns the size of the data or zero.
@end deftypefun

@subheading gnutls_record_cork
@anchor{gnutls_record_cork}
@deftypefun {void} {gnutls_record_cork} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

If called, @code{gnutls_record_send()}  will no longer send any records.
Any sent records will be cached until @code{gnutls_record_uncork()}  is called.

This function is safe to use with DTLS after GnuTLS 3.3.0.

@strong{Since:} 3.1.9
@end deftypefun

@subheading gnutls_record_disable_padding
@anchor{gnutls_record_disable_padding}
@deftypefun {void} {gnutls_record_disable_padding} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Used to disabled padding in TLS 1.0 and above.  Normally you do not
need to use this function, but there are buggy clients that
complain if a server pads the encrypted data.  This of course will
disable protection against statistical attacks on the data.

This function is defunct since 3.1.7. Random padding is disabled
by default unless requested using @code{gnutls_record_send_range()} .
@end deftypefun

@subheading gnutls_record_discard_queued
@anchor{gnutls_record_discard_queued}
@deftypefun {size_t} {gnutls_record_discard_queued} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function discards all queued to be sent packets in a DTLS session.
These are the packets queued after an interrupted @code{gnutls_record_send()} .

This function can only be used with transports where @code{send()}  is
an all-or-nothing operation (e.g., UDP). When partial writes are allowed
this function will cause session errors.

@strong{Returns:} The number of bytes discarded.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_record_get_direction
@anchor{gnutls_record_get_direction}
@deftypefun {int} {gnutls_record_get_direction} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function is useful to determine whether a GnuTLS function was interrupted
while sending or receiving, so that @code{select()}  or @code{poll()}  may be called appropriately.

It provides information about the internals of the record
protocol and is only useful if a prior gnutls function call,
e.g.  @code{gnutls_handshake()} , was interrupted and returned
@code{GNUTLS_E_INTERRUPTED}  or @code{GNUTLS_E_AGAIN} . After such an interrupt
applications may call @code{select()}  or @code{poll()}  before restoring the
interrupted GnuTLS function.

This function's output is unreliable if you are using the same
 @code{session} in different threads for sending and receiving.

@strong{Returns:} 0 if interrupted while trying to read data, or 1 while trying to write data.
@end deftypefun

@subheading gnutls_record_get_max_early_data_size
@anchor{gnutls_record_get_max_early_data_size}
@deftypefun {size_t} {gnutls_record_get_max_early_data_size} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function returns the maximum early data size in this connection.
This property can only be set to servers.  The client may be
provided with the maximum allowed size through the "early_data"
extension of the NewSessionTicket handshake message.

@strong{Returns:} The maximum early data size in this connection.

@strong{Since:} 3.6.5
@end deftypefun

@subheading gnutls_record_get_max_size
@anchor{gnutls_record_get_max_size}
@deftypefun {size_t} {gnutls_record_get_max_size} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get the record size.  The maximum record size is negotiated by the
client after the first handshake message.

@strong{Returns:} The maximum record packet size in this connection.
@end deftypefun

@subheading gnutls_record_get_state
@anchor{gnutls_record_get_state}
@deftypefun {int} {gnutls_record_get_state} (gnutls_session_t @var{session}, unsigned @var{read}, gnutls_datum_t * @var{mac_key}, gnutls_datum_t * @var{IV}, gnutls_datum_t * @var{cipher_key}, unsigned char [8] @var{seq_number})
@var{session}: is a @code{gnutls_session_t}  type

@var{read}: if non-zero the read parameters are returned, otherwise the write

@var{mac_key}: the key used for MAC (if a MAC is used)

@var{IV}: the initialization vector or nonce used

@var{cipher_key}: the cipher key

@var{seq_number}: A 64-bit sequence number

This function will return the parameters of the current record state.
These are only useful to be provided to an external off-loading device
or subsystem. The returned values should be considered constant
and valid for the lifetime of the session.

In that case, to sync the state back you must call @code{gnutls_record_set_state()} .

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.

Since 3.4.0
@end deftypefun

@subheading gnutls_record_overhead_size
@anchor{gnutls_record_overhead_size}
@deftypefun {size_t} {gnutls_record_overhead_size} (gnutls_session_t @var{session})
@var{session}: is @code{gnutls_session_t} 

This function will return the size in bytes of the overhead
due to TLS (or DTLS) per record. On certain occasions
(e.g., CBC ciphers) the returned value is the maximum
possible overhead.

@strong{Since:} 3.2.2
@end deftypefun

@subheading gnutls_record_recv
@anchor{gnutls_record_recv}
@deftypefun {ssize_t} {gnutls_record_recv} (gnutls_session_t @var{session}, void * @var{data}, size_t @var{data_size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{data}: the buffer that the data will be read into

@var{data_size}: the number of requested bytes

This function has the similar semantics with @code{recv()} .  The only
difference is that it accepts a GnuTLS session, and uses different
error codes.
In the special case that the peer requests a renegotiation, the
caller will receive an error code of @code{GNUTLS_E_REHANDSHAKE} .  In case
of a client, this message may be simply ignored, replied with an alert
@code{GNUTLS_A_NO_RENEGOTIATION} , or replied with a new handshake,
depending on the client's will. A server receiving this error code
can only initiate a new handshake or terminate the session.

If @code{EINTR}  is returned by the internal pull function (the default
is @code{recv()} ) then @code{GNUTLS_E_INTERRUPTED}  will be returned.  If
@code{GNUTLS_E_INTERRUPTED}  or @code{GNUTLS_E_AGAIN}  is returned, you must
call this function again to get the data.  See also
@code{gnutls_record_get_direction()} .

@strong{Returns:} The number of bytes received and zero on EOF (for stream
connections).  A negative error code is returned in case of an error.
The number of bytes received might be less than the requested  @code{data_size} .
@end deftypefun

@subheading gnutls_record_recv_early_data
@anchor{gnutls_record_recv_early_data}
@deftypefun {ssize_t} {gnutls_record_recv_early_data} (gnutls_session_t @var{session}, void * @var{data}, size_t @var{data_size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{data}: the buffer that the data will be read into

@var{data_size}: the number of requested bytes

This function can be used by a server to retrieve data sent early
in the handshake processes when resuming a session.  This is used
to implement a zero-roundtrip (0-RTT) mode.  It has the same
semantics as @code{gnutls_record_recv()} .

This function can be called either in a handshake hook, or after
the handshake is complete.

@strong{Returns:} The number of bytes received and zero when early data
reading is complete.  A negative error code is returned in case of
an error.  If no early data is received during the handshake, this
function returns @code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE} .  The
number of bytes received might be less than the requested
 @code{data_size} .

@strong{Since:} 3.6.5
@end deftypefun

@subheading gnutls_record_recv_packet
@anchor{gnutls_record_recv_packet}
@deftypefun {ssize_t} {gnutls_record_recv_packet} (gnutls_session_t @var{session}, gnutls_packet_t * @var{packet})
@var{session}: is a @code{gnutls_session_t}  type.

@var{packet}: the structure that will hold the packet data

This is a lower-level function than @code{gnutls_record_recv()}  and allows
to directly receive the whole decrypted packet. That avoids a
memory copy, and is intended to be used by applications seeking high
performance.

The received packet is accessed using @code{gnutls_packet_get()}  and
must be deinitialized using @code{gnutls_packet_deinit()} . The returned
packet will be @code{NULL}  if the return value is zero (EOF).

@strong{Returns:} The number of bytes received and zero on EOF (for stream
connections).  A negative error code is returned in case of an error.

@strong{Since:} 3.3.5
@end deftypefun

@subheading gnutls_record_recv_seq
@anchor{gnutls_record_recv_seq}
@deftypefun {ssize_t} {gnutls_record_recv_seq} (gnutls_session_t @var{session}, void * @var{data}, size_t @var{data_size}, unsigned char * @var{seq})
@var{session}: is a @code{gnutls_session_t}  type.

@var{data}: the buffer that the data will be read into

@var{data_size}: the number of requested bytes

@var{seq}: is the packet's 64-bit sequence number. Should have space for 8 bytes.

This function is the same as @code{gnutls_record_recv()} , except that
it returns in addition to data, the sequence number of the data.
This is useful in DTLS where record packets might be received
out-of-order. The returned 8-byte sequence number is an
integer in big-endian format and should be
treated as a unique message identification.

@strong{Returns:} The number of bytes received and zero on EOF.  A negative
error code is returned in case of an error.  The number of bytes
received might be less than  @code{data_size} .

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_record_send
@anchor{gnutls_record_send}
@deftypefun {ssize_t} {gnutls_record_send} (gnutls_session_t @var{session}, const void * @var{data}, size_t @var{data_size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{data}: contains the data to send

@var{data_size}: is the length of the data

This function has the similar semantics with @code{send()} .  The only
difference is that it accepts a GnuTLS session, and uses different
error codes.
Note that if the send buffer is full, @code{send()}  will block this
function.  See the @code{send()}  documentation for more information.

You can replace the default push function which is @code{send()} , by using
@code{gnutls_transport_set_push_function()} .

If the EINTR is returned by the internal push function
then @code{GNUTLS_E_INTERRUPTED}  will be returned. If
@code{GNUTLS_E_INTERRUPTED}  or @code{GNUTLS_E_AGAIN}  is returned, you must
call this function again with the exact same parameters, or provide a
@code{NULL}  pointer for  @code{data} and 0 for  @code{data_size} , in order to write the
same data as before. If you wish to discard the previous data instead
of retrying, you must call @code{gnutls_record_discard_queued()}  before
calling this function with different parameters. Note that the latter
works only on special transports (e.g., UDP).
cf. @code{gnutls_record_get_direction()} .

Note that in DTLS this function will return the @code{GNUTLS_E_LARGE_PACKET} 
error code if the send data exceed the data MTU value - as returned
by @code{gnutls_dtls_get_data_mtu()} . The errno value EMSGSIZE
also maps to @code{GNUTLS_E_LARGE_PACKET} .
Note that since 3.2.13 this function can be called under cork in DTLS
mode, and will refuse to send data over the MTU size by returning
@code{GNUTLS_E_LARGE_PACKET} .

@strong{Returns:} The number of bytes sent, or a negative error code.  The
number of bytes sent might be less than  @code{data_size} .  The maximum
number of bytes this function can send in a single call depends
on the negotiated maximum record size.
@end deftypefun

@subheading gnutls_record_send2
@anchor{gnutls_record_send2}
@deftypefun {ssize_t} {gnutls_record_send2} (gnutls_session_t @var{session}, const void * @var{data}, size_t @var{data_size}, size_t @var{pad}, unsigned @var{flags})
@var{session}: is a @code{gnutls_session_t}  type.

@var{data}: contains the data to send

@var{data_size}: is the length of the data

@var{pad}: padding to be added to the record

@var{flags}: must be zero

This function is identical to @code{gnutls_record_send()}  except that it
takes an extra argument to specify padding to be added the record.
To determine the maximum size of padding, use
@code{gnutls_record_get_max_size()}  and @code{gnutls_record_overhead_size()} .

Note that in order for GnuTLS to provide constant time processing
of padding and data in TLS1.3, the flag @code{GNUTLS_SAFE_PADDING_CHECK} 
must be used in @code{gnutls_init()} .

@strong{Returns:} The number of bytes sent, or a negative error code.  The
number of bytes sent might be less than  @code{data_size} .  The maximum
number of bytes this function can send in a single call depends
on the negotiated maximum record size.

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_record_send_early_data
@anchor{gnutls_record_send_early_data}
@deftypefun {ssize_t} {gnutls_record_send_early_data} (gnutls_session_t @var{session}, const void * @var{data}, size_t @var{data_size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{data}: contains the data to send

@var{data_size}: is the length of the data

This function can be used by a client to send data early in the
handshake processes when resuming a session.  This is used to
implement a zero-roundtrip (0-RTT) mode.  It has the same semantics
as @code{gnutls_record_send()} .

There may be a limit to the amount of data sent as early data.  Use
@code{gnutls_record_get_max_early_data_size()}  to check the limit.  If the
limit exceeds, this function returns
@code{GNUTLS_E_RECORD_LIMIT_REACHED} .

@strong{Returns:} The number of bytes sent, or a negative error code.  The
number of bytes sent might be less than  @code{data_size} .  The maximum
number of bytes this function can send in a single call depends
on the negotiated maximum record size.

@strong{Since:} 3.6.5
@end deftypefun

@subheading gnutls_record_send_file
@anchor{gnutls_record_send_file}
@deftypefun {ssize_t} {gnutls_record_send_file} (gnutls_session_t @var{session}, int @var{fd}, off_t * @var{offset}, size_t @var{count})
@var{session}: is a @code{gnutls_session_t}  type.

@var{fd}: file descriptor from which to read data.

@var{offset}: Is relative to file offset, denotes the starting location for
reading.  after function returns, it point to position following
last read byte.

@var{count}: is the length of the data in bytes to be read from file and send.

This function sends data from  @code{fd} . If KTLS (kernel TLS) is enabled, it will
use the @code{sendfile()}  system call to avoid overhead of copying data between user
space and the kernel. Otherwise, this functionality is merely emulated by
calling @code{read()}  and @code{gnutls_record_send()} . If this implementation is
suboptimal, check whether KTLS is enabled using
@code{gnutls_transport_is_ktls_enabled()} .

If  @code{offset} is NULL then file offset is incremented by number of bytes send,
otherwise file offset remains unchanged.

@strong{Returns:} The number of bytes sent, or a negative error code.
@end deftypefun

@subheading gnutls_record_send_range
@anchor{gnutls_record_send_range}
@deftypefun {ssize_t} {gnutls_record_send_range} (gnutls_session_t @var{session}, const void * @var{data}, size_t @var{data_size}, const gnutls_range_st * @var{range})
@var{session}: is a @code{gnutls_session_t}  type.

@var{data}: contains the data to send.

@var{data_size}: is the length of the data.

@var{range}: is the range of lengths in which the real data length must be hidden.

This function operates like @code{gnutls_record_send()}  but, while
@code{gnutls_record_send()}  adds minimal padding to each TLS record,
this function uses the TLS extra-padding feature to conceal the real
data size within the range of lengths provided.
Some TLS sessions do not support extra padding (e.g. stream ciphers in standard
TLS or SSL3 sessions). To know whether the current session supports extra
padding, and hence length hiding, use the @code{gnutls_record_can_use_length_hiding()} 
function.

@strong{Note:} This function currently is limited to blocking sockets.

@strong{Returns:} The number of bytes sent (that is data_size in a successful invocation),
or a negative error code.
@end deftypefun

@subheading gnutls_record_set_max_early_data_size
@anchor{gnutls_record_set_max_early_data_size}
@deftypefun {int} {gnutls_record_set_max_early_data_size} (gnutls_session_t @var{session}, size_t @var{size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{size}: is the new size

This function sets the maximum early data size in this connection.
This property can only be set to servers.  The client may be
provided with the maximum allowed size through the "early_data"
extension of the NewSessionTicket handshake message.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

@strong{Since:} 3.6.4
@end deftypefun

@subheading gnutls_record_set_max_recv_size
@anchor{gnutls_record_set_max_recv_size}
@deftypefun {ssize_t} {gnutls_record_set_max_recv_size} (gnutls_session_t @var{session}, size_t @var{size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{size}: is the new size

This function sets the maximum amount of plaintext received in a
record in this connection.

The limit is also negotiated through a TLS extension called 'record
size limit'.  Note that while the 'record size limit' extension is
preferred, not all TLS implementations use or even understand the
extension.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

@strong{Since:} 3.6.8
@end deftypefun

@subheading gnutls_record_set_max_size
@anchor{gnutls_record_set_max_size}
@deftypefun {ssize_t} {gnutls_record_set_max_size} (gnutls_session_t @var{session}, size_t @var{size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{size}: is the new size

This function sets the maximum amount of plaintext sent and
received in a record in this connection.

Prior to 3.6.4, this function was implemented using a TLS extension
called 'max fragment length', which limits the acceptable values to
512(=2^9), 1024(=2^10), 2048(=2^11) and 4096(=2^12).

Since 3.6.4, the limit is also negotiated through a new TLS
extension called 'record size limit', which doesn't have the
limitation, as long as the value ranges between 512 and 16384.
Note that while the 'record size limit' extension is preferred, not
all TLS implementations use or even understand the extension.

@strong{Deprecated:} if the client can assume that the 'record size limit'
extension is supported by the server, we recommend using
@code{gnutls_record_set_max_recv_size()}  instead.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_record_set_state
@anchor{gnutls_record_set_state}
@deftypefun {int} {gnutls_record_set_state} (gnutls_session_t @var{session}, unsigned @var{read}, const unsigned char [8] @var{seq_number})
@var{session}: is a @code{gnutls_session_t}  type

@var{read}: if non-zero the read parameters are returned, otherwise the write

@var{seq_number}: A 64-bit sequence number

This function will set the sequence number in the current record state.
This function is useful if sending and receiving are offloaded from
gnutls. That is, if @code{gnutls_record_get_state()}  was used.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.

Since 3.4.0
@end deftypefun

@subheading gnutls_record_set_timeout
@anchor{gnutls_record_set_timeout}
@deftypefun {void} {gnutls_record_set_timeout} (gnutls_session_t @var{session}, unsigned int @var{ms})
@var{session}: is a @code{gnutls_session_t}  type.

@var{ms}: is a timeout value in milliseconds

This function sets the receive timeout for the record layer
to the provided value. Use an  @code{ms} value of zero to disable
timeout (the default), or @code{GNUTLS_INDEFINITE_TIMEOUT} , to
set an indefinite timeout.

This function requires to set a pull timeout callback. See
@code{gnutls_transport_set_pull_timeout_function()} .

@strong{Since:} 3.1.7
@end deftypefun

@subheading gnutls_record_uncork
@anchor{gnutls_record_uncork}
@deftypefun {int} {gnutls_record_uncork} (gnutls_session_t @var{session}, unsigned int @var{flags})
@var{session}: is a @code{gnutls_session_t}  type.

@var{flags}: Could be zero or @code{GNUTLS_RECORD_WAIT} 

This resets the effect of @code{gnutls_record_cork()} , and flushes any pending
data. If the @code{GNUTLS_RECORD_WAIT}  flag is specified then this
function will block until the data is sent or a fatal error
occurs (i.e., the function will retry on @code{GNUTLS_E_AGAIN}  and
@code{GNUTLS_E_INTERRUPTED} ).

If the flag @code{GNUTLS_RECORD_WAIT}  is not specified and the function
is interrupted then the @code{GNUTLS_E_AGAIN}  or @code{GNUTLS_E_INTERRUPTED} 
errors will be returned. To obtain the data left in the corked
buffer use @code{gnutls_record_check_corked()} .

@strong{Returns:} On success the number of transmitted data is returned, or
otherwise a negative error code.

@strong{Since:} 3.1.9
@end deftypefun

@subheading gnutls_rehandshake
@anchor{gnutls_rehandshake}
@deftypefun {int} {gnutls_rehandshake} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function can only be called in server side, and
instructs a TLS 1.2 or earlier client to renegotiate
parameters (perform a handshake), by sending a
hello request message.

If this function succeeds, the calling application
should call @code{gnutls_record_recv()}  until @code{GNUTLS_E_REHANDSHAKE} 
is returned to clear any pending data. If the @code{GNUTLS_E_REHANDSHAKE} 
error code is not seen, then the handshake request was
not followed by the peer (the TLS protocol does not require
the client to do, and such compliance should be handled
by the application protocol).

Once the @code{GNUTLS_E_REHANDSHAKE}  error code is seen, the
calling application should proceed to calling
@code{gnutls_handshake()}  to negotiate the new
parameters.

If the client does not wish to renegotiate parameters he
may reply with an alert message, and in that case the return code seen
by subsequent @code{gnutls_record_recv()}  will be
@code{GNUTLS_E_WARNING_ALERT_RECEIVED}  with the specific alert being
@code{GNUTLS_A_NO_RENEGOTIATION} .  A client may also choose to ignore
this request.

Under TLS 1.3 this function is equivalent to @code{gnutls_session_key_update()} 
with the @code{GNUTLS_KU_PEER}  flag. In that case subsequent calls to
@code{gnutls_record_recv()}  will not return @code{GNUTLS_E_REHANDSHAKE} , and
calls to @code{gnutls_handshake()}  in server side are a no-op.

This function always fails with @code{GNUTLS_E_INVALID_REQUEST}  when
called in client side.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.
@end deftypefun

@subheading gnutls_safe_renegotiation_status
@anchor{gnutls_safe_renegotiation_status}
@deftypefun {unsigned} {gnutls_safe_renegotiation_status} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Can be used to check whether safe renegotiation is being used
in the current session.

@strong{Returns:} 0 when safe renegotiation is not used and non (0) when
safe renegotiation is used.

@strong{Since:} 2.10.0
@end deftypefun

@subheading gnutls_sec_param_get_name
@anchor{gnutls_sec_param_get_name}
@deftypefun {const char *} {gnutls_sec_param_get_name} (gnutls_sec_param_t @var{param})
@var{param}: is a security parameter

Convert a @code{gnutls_sec_param_t}  value to a string.

@strong{Returns:} a pointer to a string that contains the name of the
specified security level, or @code{NULL} .

@strong{Since:} 2.12.0
@end deftypefun

@subheading gnutls_sec_param_to_pk_bits
@anchor{gnutls_sec_param_to_pk_bits}
@deftypefun {unsigned int} {gnutls_sec_param_to_pk_bits} (gnutls_pk_algorithm_t @var{algo}, gnutls_sec_param_t @var{param})
@var{algo}: is a public key algorithm

@var{param}: is a security parameter

When generating private and public key pairs a difficult question
is which size of "bits" the modulus will be in RSA and the group size
in DSA. The easy answer is 1024, which is also wrong. This function
will convert a human understandable security parameter to an
appropriate size for the specific algorithm.

@strong{Returns:} The number of bits, or (0).

@strong{Since:} 2.12.0
@end deftypefun

@subheading gnutls_sec_param_to_symmetric_bits
@anchor{gnutls_sec_param_to_symmetric_bits}
@deftypefun {unsigned int} {gnutls_sec_param_to_symmetric_bits} (gnutls_sec_param_t @var{param})
@var{param}: is a security parameter

This function will return the number of bits that correspond to
symmetric cipher strength for the given security parameter.

@strong{Returns:} The number of bits, or (0).

@strong{Since:} 3.3.0
@end deftypefun

@subheading gnutls_server_name_get
@anchor{gnutls_server_name_get}
@deftypefun {int} {gnutls_server_name_get} (gnutls_session_t @var{session}, void * @var{data}, size_t * @var{data_length}, unsigned int * @var{type}, unsigned int @var{indx})
@var{session}: is a @code{gnutls_session_t}  type.

@var{data}: will hold the data

@var{data_length}: will hold the data length. Must hold the maximum size of data.

@var{type}: will hold the server name indicator type

@var{indx}: is the index of the server_name

This function will allow you to get the name indication (if any), a
client has sent.  The name indication may be any of the enumeration
gnutls_server_name_type_t.

If  @code{type} is GNUTLS_NAME_DNS, then this function is to be used by
servers that support virtual hosting, and the data will be a null
terminated IDNA ACE string (prior to GnuTLS 3.4.0 it was a UTF-8 string).

If  @code{data} has not enough size to hold the server name
GNUTLS_E_SHORT_MEMORY_BUFFER is returned, and  @code{data_length} will
hold the required size.

 @code{indx} is used to retrieve more than one server names (if sent by
the client).  The first server name has an index of 0, the second 1
and so on.  If no name with the given index exists
GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE is returned.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, on UTF-8
decoding error @code{GNUTLS_E_IDNA_ERROR}  is returned, otherwise a negative
error code is returned.
@end deftypefun

@subheading gnutls_server_name_set
@anchor{gnutls_server_name_set}
@deftypefun {int} {gnutls_server_name_set} (gnutls_session_t @var{session}, gnutls_server_name_type_t @var{type}, const void * @var{name}, size_t @var{name_length})
@var{session}: is a @code{gnutls_session_t}  type.

@var{type}: specifies the indicator type

@var{name}: is a string that contains the server name.

@var{name_length}: holds the length of name excluding the terminating null byte

This function is to be used by clients that want to inform (via a
TLS extension mechanism) the server of the name they connected to.
This should be used by clients that connect to servers that do
virtual hosting.

The value of  @code{name} depends on the  @code{type} type.  In case of
@code{GNUTLS_NAME_DNS} , a UTF-8 null-terminated domain name string,
without the trailing dot, is expected.

IPv4 or IPv6 addresses are not permitted to be set by this function.
If the function is called with a name of  @code{name_length} zero it will clear
all server names set.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.
@end deftypefun

@subheading gnutls_session_channel_binding
@anchor{gnutls_session_channel_binding}
@deftypefun {int} {gnutls_session_channel_binding} (gnutls_session_t @var{session}, gnutls_channel_binding_t @var{cbtype}, gnutls_datum_t * @var{cb})
@var{session}: is a @code{gnutls_session_t}  type.

@var{cbtype}: an @code{gnutls_channel_binding_t}  enumeration type

@var{cb}: output buffer array with data

Extract given channel binding data of the  @code{cbtype} (e.g.,
@code{GNUTLS_CB_TLS_UNIQUE} ) type.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success,
@code{GNUTLS_E_UNIMPLEMENTED_FEATURE}  if the  @code{cbtype} is unsupported,
@code{GNUTLS_E_CHANNEL_BINDING_NOT_AVAILABLE}  if the data is not
currently available, or an error code.

@strong{Since:} 2.12.0
@end deftypefun

@subheading gnutls_session_enable_compatibility_mode
@anchor{gnutls_session_enable_compatibility_mode}
@deftypefun {void} {gnutls_session_enable_compatibility_mode} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function can be used to disable certain (security) features in
TLS in order to maintain maximum compatibility with buggy
clients. Because several trade-offs with security are enabled,
if required they will be reported through the audit subsystem.

Normally only servers that require maximum compatibility with
everything out there, need to call this function.

Note that this function must be called after any call to gnutls_priority
functions.

@strong{Since:} 2.1.4
@end deftypefun

@subheading gnutls_session_etm_status
@anchor{gnutls_session_etm_status}
@deftypefun {unsigned} {gnutls_session_etm_status} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get the status of the encrypt-then-mac extension negotiation.
This is in accordance to rfc7366

@strong{Returns:} Non-zero if the negotiation was successful or zero otherwise.
@end deftypefun

@subheading gnutls_session_ext_master_secret_status
@anchor{gnutls_session_ext_master_secret_status}
@deftypefun {unsigned} {gnutls_session_ext_master_secret_status} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get the status of the extended master secret extension negotiation.
This is in accordance to RFC7627. That information is also
available to the more generic @code{gnutls_session_get_flags()} .

@strong{Returns:} Non-zero if the negotiation was successful or zero otherwise.
@end deftypefun

@subheading gnutls_session_ext_register
@anchor{gnutls_session_ext_register}
@deftypefun {int} {gnutls_session_ext_register} (gnutls_session_t @var{session}, const char * @var{name}, int @var{id}, gnutls_ext_parse_type_t @var{parse_point}, gnutls_ext_recv_func @var{recv_func}, gnutls_ext_send_func @var{send_func}, gnutls_ext_deinit_data_func @var{deinit_func}, gnutls_ext_pack_func @var{pack_func}, gnutls_ext_unpack_func @var{unpack_func}, unsigned @var{flags})
@var{session}: the session for which this extension will be set

@var{name}: the name of the extension to register

@var{id}: the numeric id of the extension

@var{parse_point}: the parse type of the extension (see gnutls_ext_parse_type_t)

@var{recv_func}: a function to receive the data

@var{send_func}: a function to send the data

@var{deinit_func}: a function deinitialize any private data

@var{pack_func}: a function which serializes the extension's private data (used on session packing for resumption)

@var{unpack_func}: a function which will deserialize the extension's private data

@var{flags}: must be zero or flags from @code{gnutls_ext_flags_t} 

This function will register a new extension type. The extension will be
only usable within the registered session. If the extension type
is already registered then @code{GNUTLS_E_ALREADY_REGISTERED}  will be returned,
unless the flag @code{GNUTLS_EXT_FLAG_OVERRIDE_INTERNAL}  is specified. The latter
flag when specified can be used to override certain extensions introduced
after 3.6.0. It is expected to be used by applications which handle
custom extensions that are not currently supported in GnuTLS, but direct
support for them may be added in the future.

Each registered extension can store temporary data into the gnutls_session_t
structure using @code{gnutls_ext_set_data()} , and they can be retrieved using
@code{gnutls_ext_get_data()} .

The validity of the extension registered can be given by the appropriate flags
of @code{gnutls_ext_flags_t} . If no validity is given, then the registered extension
will be valid for client and TLS1.2 server hello (or encrypted extensions for TLS1.3).

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.5.5
@end deftypefun

@subheading gnutls_session_force_valid
@anchor{gnutls_session_force_valid}
@deftypefun {void} {gnutls_session_force_valid} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Clears the invalid flag in a session. That means
that sessions were corrupt or invalid data were received 
can be re-used. Use only when debugging or experimenting
with the TLS protocol. Should not be used in typical
applications.
@end deftypefun

@subheading gnutls_session_get_data
@anchor{gnutls_session_get_data}
@deftypefun {int} {gnutls_session_get_data} (gnutls_session_t @var{session}, void * @var{session_data}, size_t * @var{session_data_size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{session_data}: is a pointer to space to hold the session.

@var{session_data_size}: is the session_data's size, or it will be set by the function.

Returns all session parameters needed to be stored to support resumption,
in a pre-allocated buffer.

See @code{gnutls_session_get_data2()}  for more information.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_session_get_data2
@anchor{gnutls_session_get_data2}
@deftypefun {int} {gnutls_session_get_data2} (gnutls_session_t @var{session}, gnutls_datum_t * @var{data})
@var{session}: is a @code{gnutls_session_t}  type.

@var{data}: is a pointer to a datum that will hold the session.

Returns necessary parameters to support resumption. The client
should call this function and store the returned session data. A session
can be resumed later by calling @code{gnutls_session_set_data()}  with the returned
data. Note that under TLS 1.3, it is recommended for clients to use
session parameters only once, to prevent passive-observers from correlating
the different connections.

The returned  @code{data} are allocated and must be released using @code{gnutls_free()} .

This function will fail if called prior to handshake completion. In
case of false start TLS, the handshake completes only after data have
been successfully received from the peer.

Under TLS1.3 session resumption is possible only after a session ticket
is received by the client. To ensure that such a ticket has been received use
@code{gnutls_session_get_flags()}  and check for flag @code{GNUTLS_SFLAGS_SESSION_TICKET} ;
if this flag is not set, this function will wait for a new ticket within
an estimated roundtrip, and if not received will return dummy data which
cannot lead to resumption.

To get notified when new tickets are received by the server
use @code{gnutls_handshake_set_hook_function()}  to wait for @code{GNUTLS_HANDSHAKE_NEW_SESSION_TICKET} 
messages. Each call of @code{gnutls_session_get_data2()}  after a ticket is
received, will return session resumption data corresponding to the last
received ticket.

Note that this function under TLS1.3 requires a callback to be set with
@code{gnutls_transport_set_pull_timeout_function()}  for successful operation. There
was a bug before 3.6.10 which could make this function fail if that callback
was not set. On later versions if not set, the function will return a successful
error code, but will return dummy data that cannot lead to a resumption.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_session_get_desc
@anchor{gnutls_session_get_desc}
@deftypefun {char *} {gnutls_session_get_desc} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

This function returns a string describing the current session.
The string is null terminated and allocated using @code{gnutls_malloc()} .

If initial negotiation is not complete when this function is called,
@code{NULL}  will be returned.

@strong{Returns:} a description of the protocols and algorithms in the current session.

@strong{Since:} 3.1.10
@end deftypefun

@subheading gnutls_session_get_flags
@anchor{gnutls_session_get_flags}
@deftypefun {unsigned} {gnutls_session_get_flags} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

This function will return a series (ORed) of flags, applicable
for the current session.

This replaces individual informational functions such as
@code{gnutls_safe_renegotiation_status()} , @code{gnutls_session_ext_master_secret_status()} ,
etc.

@strong{Returns:} An ORed sequence of flags (see @code{gnutls_session_flags_t} )

@strong{Since:} 3.5.0
@end deftypefun

@subheading gnutls_session_get_id
@anchor{gnutls_session_get_id}
@deftypefun {int} {gnutls_session_get_id} (gnutls_session_t @var{session}, void * @var{session_id}, size_t * @var{session_id_size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{session_id}: is a pointer to space to hold the session id.

@var{session_id_size}: initially should contain the maximum  @code{session_id} size and will be updated.

Returns the TLS session identifier. The session ID is selected by the
server, and in older versions of TLS was a unique identifier shared
between client and server which was persistent across resumption.
In the latest version of TLS (1.3) or TLS with session tickets, the
notion of session identifiers is undefined and cannot be relied for uniquely
identifying sessions across client and server.

In client side this function returns the identifier returned by the
server, and cannot be assumed to have any relation to session resumption.
In server side this function is guaranteed to return a persistent
identifier of the session since GnuTLS 3.6.4, which may not necessarily
map into the TLS session ID value. Prior to that version the value
could only be considered a persistent identifier, under TLS1.2 or earlier
and when no session tickets were in use.

The session identifier value returned is always less than
@code{GNUTLS_MAX_SESSION_ID_SIZE} .

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_session_get_id2
@anchor{gnutls_session_get_id2}
@deftypefun {int} {gnutls_session_get_id2} (gnutls_session_t @var{session}, gnutls_datum_t * @var{session_id})
@var{session}: is a @code{gnutls_session_t}  type.

@var{session_id}: will point to the session ID.

Returns the TLS session identifier. The session ID is selected by the
server, and in older versions of TLS was a unique identifier shared
between client and server which was persistent across resumption.
In the latest version of TLS (1.3) or TLS 1.2 with session tickets, the
notion of session identifiers is undefined and cannot be relied for uniquely
identifying sessions across client and server.

In client side this function returns the identifier returned by the
server, and cannot be assumed to have any relation to session resumption.
In server side this function is guaranteed to return a persistent
identifier of the session since GnuTLS 3.6.4, which may not necessarily
map into the TLS session ID value. Prior to that version the value
could only be considered a persistent identifier, under TLS1.2 or earlier
and when no session tickets were in use.

The session identifier value returned is always less than
@code{GNUTLS_MAX_SESSION_ID_SIZE}  and should be treated as constant.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.

@strong{Since:} 3.1.4
@end deftypefun

@subheading gnutls_session_get_keylog_function
@anchor{gnutls_session_get_keylog_function}
@deftypefun {gnutls_keylog_func} {gnutls_session_get_keylog_function} (const gnutls_session_t @var{session})
@var{session}: is @code{gnutls_session_t}  type

This function will return the callback function set using
@code{gnutls_session_set_keylog_function()} .

@strong{Returns:} The function set or @code{NULL}  otherwise.

@strong{Since:} 3.6.13
@end deftypefun

@subheading gnutls_session_get_master_secret
@anchor{gnutls_session_get_master_secret}
@deftypefun {void} {gnutls_session_get_master_secret} (gnutls_session_t @var{session}, gnutls_datum_t * @var{secret})
@var{session}: is a @code{gnutls_session_t}  type.

@var{secret}: the session's master secret

This function returns pointers to the master secret
used in the TLS session. The pointers are not to be modified or deallocated.

This function is only applicable under TLS 1.2 or earlier versions.

@strong{Since:} 3.5.0
@end deftypefun

@subheading gnutls_session_get_ptr
@anchor{gnutls_session_get_ptr}
@deftypefun {void *} {gnutls_session_get_ptr} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Get user pointer for session.  Useful in callbacks.  This is the
pointer set with @code{gnutls_session_set_ptr()} .

@strong{Returns:} the user given pointer from the session structure, or
@code{NULL}  if it was never set.
@end deftypefun

@subheading gnutls_session_get_random
@anchor{gnutls_session_get_random}
@deftypefun {void} {gnutls_session_get_random} (gnutls_session_t @var{session}, gnutls_datum_t * @var{client}, gnutls_datum_t * @var{server})
@var{session}: is a @code{gnutls_session_t}  type.

@var{client}: the client part of the random

@var{server}: the server part of the random

This function returns pointers to the client and server
random fields used in the TLS handshake. The pointers are
not to be modified or deallocated.

If a client random value has not yet been established, the output
will be garbage.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_session_get_verify_cert_status
@anchor{gnutls_session_get_verify_cert_status}
@deftypefun {unsigned int} {gnutls_session_get_verify_cert_status} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

This function returns the status of the verification when initiated
via auto-verification, i.e., by @code{gnutls_session_set_verify_cert2()}  or
@code{gnutls_session_set_verify_cert()} . If no certificate verification
was occurred then the return value would be set to ((unsigned int)-1).

The certificate verification status is the same as in @code{gnutls_certificate_verify_peers()} .

@strong{Returns:} the certificate verification status.

@strong{Since:} 3.4.6
@end deftypefun

@subheading gnutls_session_is_resumed
@anchor{gnutls_session_is_resumed}
@deftypefun {int} {gnutls_session_is_resumed} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Checks whether session is resumed or not. This is functional
for both server and client side.

@strong{Returns:} non zero if this session is resumed, or a zero if this is
a new session.
@end deftypefun

@subheading gnutls_session_key_update
@anchor{gnutls_session_key_update}
@deftypefun {int} {gnutls_session_key_update} (gnutls_session_t @var{session}, unsigned @var{flags})
@var{session}: is a @code{gnutls_session_t}  type.

@var{flags}: zero of @code{GNUTLS_KU_PEER} 

This function will update/refresh the session keys when the
TLS protocol is 1.3 or better. The peer is notified of the
update by sending a message, so this function should be
treated similarly to @code{gnutls_record_send()}  --i.e., it may
return @code{GNUTLS_E_AGAIN}  or @code{GNUTLS_E_INTERRUPTED} .

When this flag @code{GNUTLS_KU_PEER}  is specified, this function
in addition to updating the local keys, will ask the peer to
refresh its keys too.

If the negotiated version is not TLS 1.3 or better this
function will return @code{GNUTLS_E_INVALID_REQUEST} .

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_session_resumption_requested
@anchor{gnutls_session_resumption_requested}
@deftypefun {int} {gnutls_session_resumption_requested} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Check whether the client has asked for session resumption.
This function is valid only on server side.

@strong{Returns:} non zero if session resumption was asked, or a zero if not.
@end deftypefun

@subheading gnutls_session_set_data
@anchor{gnutls_session_set_data}
@deftypefun {int} {gnutls_session_set_data} (gnutls_session_t @var{session}, const void * @var{session_data}, size_t @var{session_data_size})
@var{session}: is a @code{gnutls_session_t}  type.

@var{session_data}: is a pointer to space to hold the session.

@var{session_data_size}: is the session's size

Sets all session parameters, in order to resume a previously
established session.  The session data given must be the one
returned by @code{gnutls_session_get_data()} .  This function should be
called before @code{gnutls_handshake()} .

Keep in mind that session resuming is advisory. The server may
choose not to resume the session, thus a full handshake will be
performed.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_session_set_id
@anchor{gnutls_session_set_id}
@deftypefun {int} {gnutls_session_set_id} (gnutls_session_t @var{session}, const gnutls_datum_t * @var{sid})
@var{session}: is a @code{gnutls_session_t}  type.

@var{sid}: the session identifier

This function sets the session ID to be used in a client hello.
This is a function intended for exceptional uses. Do not use this
function unless you are implementing a custom protocol.

To set session resumption parameters use @code{gnutls_session_set_data()}  instead.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.

@strong{Since:} 3.2.1
@end deftypefun

@subheading gnutls_session_set_keylog_function
@anchor{gnutls_session_set_keylog_function}
@deftypefun {void} {gnutls_session_set_keylog_function} (gnutls_session_t @var{session}, gnutls_keylog_func @var{func})
@var{session}: is @code{gnutls_session_t}  type

@var{func}: is the function to be called

This function will set a callback to be called when a new secret is
derived and installed during handshake.

@strong{Since:} 3.6.13
@end deftypefun

@subheading gnutls_session_set_premaster
@anchor{gnutls_session_set_premaster}
@deftypefun {int} {gnutls_session_set_premaster} (gnutls_session_t @var{session}, unsigned int @var{entity}, gnutls_protocol_t @var{version}, gnutls_kx_algorithm_t @var{kx}, gnutls_cipher_algorithm_t @var{cipher}, gnutls_mac_algorithm_t @var{mac}, gnutls_compression_method_t @var{comp}, const gnutls_datum_t * @var{master}, const gnutls_datum_t * @var{session_id})
@var{session}: is a @code{gnutls_session_t}  type.

@var{entity}: GNUTLS_SERVER or GNUTLS_CLIENT

@var{version}: the TLS protocol version

@var{kx}: the key exchange method

@var{cipher}: the cipher

@var{mac}: the MAC algorithm

@var{comp}: the compression method (ignored)

@var{master}: the master key to use

@var{session_id}: the session identifier

This function sets the premaster secret in a session. This is
a function intended for exceptional uses. Do not use this
function unless you are implementing a legacy protocol.
Use @code{gnutls_session_set_data()}  instead.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun

@subheading gnutls_session_set_ptr
@anchor{gnutls_session_set_ptr}
@deftypefun {void} {gnutls_session_set_ptr} (gnutls_session_t @var{session}, void * @var{ptr})
@var{session}: is a @code{gnutls_session_t}  type.

@var{ptr}: is the user pointer

This function will set (associate) the user given pointer  @code{ptr} to
the session structure.  This pointer can be accessed with
@code{gnutls_session_get_ptr()} .
@end deftypefun

@subheading gnutls_session_set_verify_cert
@anchor{gnutls_session_set_verify_cert}
@deftypefun {void} {gnutls_session_set_verify_cert} (gnutls_session_t @var{session}, const char * @var{hostname}, unsigned @var{flags})
@var{session}: is a gnutls session

@var{hostname}: is the expected name of the peer; may be @code{NULL} 

@var{flags}: flags for certificate verification -- @code{gnutls_certificate_verify_flags} 

This function instructs GnuTLS to verify the peer's certificate
using the provided hostname. If the verification fails the handshake
will also fail with @code{GNUTLS_E_CERTIFICATE_VERIFICATION_ERROR} . In that
case the verification result can be obtained using @code{gnutls_session_get_verify_cert_status()} .

The  @code{hostname} pointer provided must remain valid for the lifetime
of the session. More precisely it should be available during any subsequent
handshakes. If no hostname is provided, no hostname verification
will be performed. For a more advanced verification function check
@code{gnutls_session_set_verify_cert2()} .

If  @code{flags} is provided which contain a profile, this function should be
called after any session priority setting functions.

The @code{gnutls_session_set_verify_cert()}  function is intended to be used by TLS
clients to verify the server's certificate.

@strong{Since:} 3.4.6
@end deftypefun

@subheading gnutls_session_set_verify_cert2
@anchor{gnutls_session_set_verify_cert2}
@deftypefun {void} {gnutls_session_set_verify_cert2} (gnutls_session_t @var{session}, gnutls_typed_vdata_st * @var{data}, unsigned @var{elements}, unsigned @var{flags})
@var{session}: is a gnutls session

@var{data}: an array of typed data

@var{elements}: the number of data elements

@var{flags}: flags for certificate verification -- @code{gnutls_certificate_verify_flags} 

This function instructs GnuTLS to verify the peer's certificate
using the provided typed data information. If the verification fails the handshake
will also fail with @code{GNUTLS_E_CERTIFICATE_VERIFICATION_ERROR} . In that
case the verification result can be obtained using @code{gnutls_session_get_verify_cert_status()} .

The acceptable typed data are the same as in @code{gnutls_certificate_verify_peers()} ,
and once set must remain valid for the lifetime of the session. More precisely
they should be available during any subsequent handshakes.

If  @code{flags} is provided which contain a profile, this function should be
called after any session priority setting functions.

@strong{Since:} 3.4.6
@end deftypefun

@subheading gnutls_session_set_verify_function
@anchor{gnutls_session_set_verify_function}
@deftypefun {void} {gnutls_session_set_verify_function} (gnutls_session_t @var{session}, gnutls_certificate_verify_function * @var{func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{func}: is the callback function

This function sets a callback to be called when peer's certificate
has been received in order to verify it on receipt rather than
doing after the handshake is completed. This overrides any callback
set using @code{gnutls_certificate_set_verify_function()} .

The callback's function prototype is:
int (*callback)(gnutls_session_t);

If the callback function is provided then gnutls will call it, in the
handshake, just after the certificate message has been received.
To verify or obtain the certificate the @code{gnutls_certificate_verify_peers2()} ,
@code{gnutls_certificate_type_get()} , @code{gnutls_certificate_get_peers()}  functions
can be used.

The callback function should return 0 for the handshake to continue
or non-zero to terminate.

@strong{Since:} 3.4.6
@end deftypefun

@subheading gnutls_session_supplemental_register
@anchor{gnutls_session_supplemental_register}
@deftypefun {int} {gnutls_session_supplemental_register} (gnutls_session_t @var{session}, const char * @var{name}, gnutls_supplemental_data_format_type_t @var{type}, gnutls_supp_recv_func @var{recv_func}, gnutls_supp_send_func @var{send_func}, unsigned @var{flags})
@var{session}: the session for which this will be registered

@var{name}: the name of the supplemental data to register

@var{type}: the type of the supplemental data format

@var{recv_func}: the function to receive the data

@var{send_func}: the function to send the data

@var{flags}: must be zero

This function will register a new supplemental data type (rfc4680).
The registered supplemental functions will be used for that specific
session. The provided  @code{type} must be an unassigned type in
@code{gnutls_supplemental_data_format_type_t} .

If the type is already registered or handled by GnuTLS internally
@code{GNUTLS_E_ALREADY_REGISTERED}  will be returned.

As supplemental data are not defined under TLS 1.3, this function will
disable TLS 1.3 support for the given session.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.5.5
@end deftypefun

@subheading gnutls_session_ticket_enable_client
@anchor{gnutls_session_ticket_enable_client}
@deftypefun {int} {gnutls_session_ticket_enable_client} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Request that the client should attempt session resumption using
SessionTicket. This call is typically unnecessary as session
tickets are enabled by default.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, or an
error code.

@strong{Since:} 2.10.0
@end deftypefun

@subheading gnutls_session_ticket_enable_server
@anchor{gnutls_session_ticket_enable_server}
@deftypefun {int} {gnutls_session_ticket_enable_server} (gnutls_session_t @var{session}, const gnutls_datum_t * @var{key})
@var{session}: is a @code{gnutls_session_t}  type.

@var{key}: key to encrypt session parameters.

Request that the server should attempt session resumption using
session tickets, i.e., by delegating storage to the client.
 @code{key} must be initialized using @code{gnutls_session_ticket_key_generate()} .
To avoid leaking that key, use @code{gnutls_memset()}  prior to
releasing it.

The default ticket expiration time can be overridden using
@code{gnutls_db_set_cache_expiration()} .

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, or an
error code.

@strong{Since:} 2.10.0
@end deftypefun

@subheading gnutls_session_ticket_key_generate
@anchor{gnutls_session_ticket_key_generate}
@deftypefun {int} {gnutls_session_ticket_key_generate} (gnutls_datum_t * @var{key})
@var{key}: is a pointer to a @code{gnutls_datum_t}  which will contain a newly
created key.

Generate a random key to encrypt security parameters within
SessionTicket.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, or an
error code.

@strong{Since:} 2.10.0
@end deftypefun

@subheading gnutls_session_ticket_send
@anchor{gnutls_session_ticket_send}
@deftypefun {int} {gnutls_session_ticket_send} (gnutls_session_t @var{session}, unsigned @var{nr}, unsigned @var{flags})
@var{session}: is a @code{gnutls_session_t}  type.

@var{nr}: the number of tickets to send

@var{flags}: must be zero

Sends a fresh session ticket to the peer. This is relevant only
in server side under TLS1.3. This function may also return @code{GNUTLS_E_AGAIN} 
or @code{GNUTLS_E_INTERRUPTED}  and in that case it must be called again.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or a negative error code.
@end deftypefun

@subheading gnutls_set_default_priority
@anchor{gnutls_set_default_priority}
@deftypefun {int} {gnutls_set_default_priority} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Sets the default priority on the ciphers, key exchange methods,
and macs. This is the recommended method of
setting the defaults, in order to promote consistency between applications
using GnuTLS, and to allow GnuTLS using applications to update settings
in par with the library. For client applications which require
maximum compatibility consider calling @code{gnutls_session_enable_compatibility_mode()} 
after this function.

For an application to specify additional options to priority string
consider using @code{gnutls_set_default_priority_append()} .

To allow a user to override the defaults (e.g., when a user interface
or configuration file is available), the functions
@code{gnutls_priority_set_direct()}  or @code{gnutls_priority_set()}  can
be used.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.

@strong{Since:} 2.1.4
@end deftypefun

@subheading gnutls_set_default_priority_append
@anchor{gnutls_set_default_priority_append}
@deftypefun {int} {gnutls_set_default_priority_append} (gnutls_session_t @var{session}, const char * @var{add_prio}, const char ** @var{err_pos}, unsigned @var{flags})
@var{session}: is a @code{gnutls_session_t}  type.

@var{add_prio}: is a string describing priorities to be appended to default

@var{err_pos}: In case of an error this will have the position in the string the error occurred

@var{flags}: must be zero

Sets the default priority on the ciphers, key exchange methods,
and macs with the additional options in  @code{add_prio} . This is the recommended method of
setting the defaults when only few additional options are to be added. This promotes
consistency between applications using GnuTLS, and allows GnuTLS using applications
to update settings in par with the library.

The  @code{add_prio} string should start as a normal priority string, e.g.,
'-VERS-TLS-ALL:+VERS-TLS1.3:%COMPAT' or '%FORCE_ETM'. That is, it must not start
with ':'.

To allow a user to override the defaults (e.g., when a user interface
or configuration file is available), the functions
@code{gnutls_priority_set_direct()}  or @code{gnutls_priority_set()}  can
be used.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, or an error code.

@strong{Since:} 3.6.3
@end deftypefun

@subheading gnutls_sign_algorithm_get
@anchor{gnutls_sign_algorithm_get}
@deftypefun {int} {gnutls_sign_algorithm_get} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Returns the signature algorithm that is (or will be) used in this
session by the server to sign data. This function should be
used only with TLS 1.2 or later.

@strong{Returns:} The sign algorithm or @code{GNUTLS_SIGN_UNKNOWN} .

@strong{Since:} 3.1.1
@end deftypefun

@subheading gnutls_sign_algorithm_get_client
@anchor{gnutls_sign_algorithm_get_client}
@deftypefun {int} {gnutls_sign_algorithm_get_client} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Returns the signature algorithm that is (or will be) used in this
session by the client to sign data. This function should be
used only with TLS 1.2 or later.

@strong{Returns:} The sign algorithm or @code{GNUTLS_SIGN_UNKNOWN} .

@strong{Since:} 3.1.11
@end deftypefun

@subheading gnutls_sign_algorithm_get_requested
@anchor{gnutls_sign_algorithm_get_requested}
@deftypefun {int} {gnutls_sign_algorithm_get_requested} (gnutls_session_t @var{session}, size_t @var{indx}, gnutls_sign_algorithm_t * @var{algo})
@var{session}: is a @code{gnutls_session_t}  type.

@var{indx}: is an index of the signature algorithm to return

@var{algo}: the returned certificate type will be stored there

Returns the signature algorithm specified by index that was
requested by the peer. If the specified index has no data available
this function returns @code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE} .  If
the negotiated TLS version does not support signature algorithms
then @code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE}  will be returned even
for the first index.  The first index is 0.

This function is useful in the certificate callback functions
to assist in selecting the correct certificate.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.

@strong{Since:} 2.10.0
@end deftypefun

@subheading gnutls_sign_get_hash_algorithm
@anchor{gnutls_sign_get_hash_algorithm}
@deftypefun {gnutls_digest_algorithm_t} {gnutls_sign_get_hash_algorithm} (gnutls_sign_algorithm_t @var{sign})
@var{sign}: is a signature algorithm

This function returns the digest algorithm corresponding to
the given signature algorithms.

@strong{Since:} 3.1.1

@strong{Returns:} return a @code{gnutls_digest_algorithm_t}  value, or @code{GNUTLS_DIG_UNKNOWN}  on error.
@end deftypefun

@subheading gnutls_sign_get_id
@anchor{gnutls_sign_get_id}
@deftypefun {gnutls_sign_algorithm_t} {gnutls_sign_get_id} (const char * @var{name})
@var{name}: is a sign algorithm name

The names are compared in a case insensitive way.

@strong{Returns:} return a @code{gnutls_sign_algorithm_t}  value corresponding to
the specified algorithm, or @code{GNUTLS_SIGN_UNKNOWN}  on error.
@end deftypefun

@subheading gnutls_sign_get_name
@anchor{gnutls_sign_get_name}
@deftypefun {const char *} {gnutls_sign_get_name} (gnutls_sign_algorithm_t @var{algorithm})
@var{algorithm}: is a sign algorithm

Convert a @code{gnutls_sign_algorithm_t}  value to a string.

@strong{Returns:} a string that contains the name of the specified sign
algorithm, or @code{NULL} .
@end deftypefun

@subheading gnutls_sign_get_oid
@anchor{gnutls_sign_get_oid}
@deftypefun {const char *} {gnutls_sign_get_oid} (gnutls_sign_algorithm_t @var{sign})
@var{sign}: is a sign algorithm

Convert a @code{gnutls_sign_algorithm_t}  value to its object identifier.

@strong{Returns:} a string that contains the object identifier of the specified sign
algorithm, or @code{NULL} .

@strong{Since:} 3.4.3
@end deftypefun

@subheading gnutls_sign_get_pk_algorithm
@anchor{gnutls_sign_get_pk_algorithm}
@deftypefun {gnutls_pk_algorithm_t} {gnutls_sign_get_pk_algorithm} (gnutls_sign_algorithm_t @var{sign})
@var{sign}: is a signature algorithm

This function returns the public key algorithm corresponding to
the given signature algorithms. Note that there may be multiple
public key algorithms supporting a particular signature type;
when dealing with such algorithms use instead @code{gnutls_sign_supports_pk_algorithm()} .

@strong{Since:} 3.1.1

@strong{Returns:} return a @code{gnutls_pk_algorithm_t}  value, or @code{GNUTLS_PK_UNKNOWN}  on error.
@end deftypefun

@subheading gnutls_sign_is_secure
@anchor{gnutls_sign_is_secure}
@deftypefun {unsigned} {gnutls_sign_is_secure} (gnutls_sign_algorithm_t @var{algorithm})
@var{algorithm}: is a sign algorithm


@strong{Returns:} Non-zero if the provided signature algorithm is considered to be secure.
@end deftypefun

@subheading gnutls_sign_is_secure2
@anchor{gnutls_sign_is_secure2}
@deftypefun {unsigned} {gnutls_sign_is_secure2} (gnutls_sign_algorithm_t @var{algorithm}, unsigned int @var{flags})
@var{algorithm}: is a sign algorithm

@var{flags}: zero or @code{GNUTLS_SIGN_FLAG_SECURE_FOR_CERTS} 


@strong{Returns:} Non-zero if the provided signature algorithm is considered to be secure.
@end deftypefun

@subheading gnutls_sign_list
@anchor{gnutls_sign_list}
@deftypefun {const gnutls_sign_algorithm_t *} {gnutls_sign_list} ( @var{void})

Get a list of supported public key signature algorithms.
This function is not thread safe.

@strong{Returns:} a (0)-terminated list of @code{gnutls_sign_algorithm_t} 
integers indicating the available ciphers.
@end deftypefun

@subheading gnutls_sign_set_secure
@anchor{gnutls_sign_set_secure}
@deftypefun {int} {gnutls_sign_set_secure} (gnutls_sign_algorithm_t @var{sign}, unsigned int @var{secure})
@var{sign}: the sign algorithm

@var{secure}: whether to mark the sign algorithm secure

Modify the previous system wide setting that marked  @code{sign} as secure
or insecure.  Calling this function is allowed
only if allowlisting mode is set in the configuration file,
and only if the system-wide TLS priority string
has not been initialized yet.
The intended usage is to provide applications with a way
to expressly deviate from the distribution or site defaults
inherited from the configuration file.
The modification is composable with further modifications
performed through the priority string mechanism.

This function is not thread-safe and is intended to be called
in the main thread at the beginning of the process execution.

Even when  @code{secure} is true,  @code{sign} is not marked as secure for the
use in certificates.  Use @code{gnutls_sign_set_secure_for_certs()}  to
mark it secure as well for certificates.

@strong{Returns:} 0 on success or negative error code otherwise.

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_sign_set_secure_for_certs
@anchor{gnutls_sign_set_secure_for_certs}
@deftypefun {int} {gnutls_sign_set_secure_for_certs} (gnutls_sign_algorithm_t @var{sign}, unsigned int @var{secure})
@var{sign}: the sign algorithm

@var{secure}: whether to mark the sign algorithm secure for certificates

Modify the previous system wide setting that marked  @code{sign} as secure
or insecure for the use in certificates.  Calling this fuction is allowed
only if allowlisting mode is set in the configuration file,
and only if the system-wide TLS priority string
has not been initialized yet.
The intended usage is to provide applications with a way
to expressly deviate from the distribution or site defaults
inherited from the configuration file.
The modification is composable with further modifications
performed through the priority string mechanism.

This function is not thread-safe and is intended to be called
in the main thread at the beginning of the process execution.
When  @code{secure} is true,  @code{sign} is marked as secure for any use unlike
@code{gnutls_sign_set_secure()} .  Otherwise, it is marked as insecure only
for the use in certificates.  Use @code{gnutls_sign_set_secure()}  to mark
it insecure for any uses.

@strong{Returns:} 0 on success or negative error code otherwise.

@strong{Since:} 3.7.3
@end deftypefun

@subheading gnutls_sign_supports_pk_algorithm
@anchor{gnutls_sign_supports_pk_algorithm}
@deftypefun {unsigned} {gnutls_sign_supports_pk_algorithm} (gnutls_sign_algorithm_t @var{sign}, gnutls_pk_algorithm_t @var{pk})
@var{sign}: is a signature algorithm

@var{pk}: is a public key algorithm

This function returns non-zero if the public key algorithm corresponds to
the given signature algorithm. That is, if that signature can be generated
from the given private key algorithm.

@strong{Since:} 3.6.0

@strong{Returns:} return non-zero when the provided algorithms are compatible.
@end deftypefun

@subheading gnutls_srp_allocate_client_credentials
@anchor{gnutls_srp_allocate_client_credentials}
@deftypefun {int} {gnutls_srp_allocate_client_credentials} (gnutls_srp_client_credentials_t *            @var{sc})
@var{sc}: is a pointer to a @code{gnutls_srp_server_credentials_t}  type.

Allocate a gnutls_srp_client_credentials_t structure.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, or an
error code.
@end deftypefun

@subheading gnutls_srp_allocate_server_credentials
@anchor{gnutls_srp_allocate_server_credentials}
@deftypefun {int} {gnutls_srp_allocate_server_credentials} (gnutls_srp_server_credentials_t *            @var{sc})
@var{sc}: is a pointer to a @code{gnutls_srp_server_credentials_t}  type.

Allocate a gnutls_srp_server_credentials_t structure.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, or an
error code.
@end deftypefun

@subheading gnutls_srp_base64_decode
@anchor{gnutls_srp_base64_decode}
@deftypefun {int} {gnutls_srp_base64_decode} (const gnutls_datum_t * @var{b64_data}, char * @var{result}, size_t * @var{result_size})
@var{b64_data}: contain the encoded data

@var{result}: the place where decoded data will be copied

@var{result_size}: holds the size of the result

This function will decode the given encoded data, using the base64
encoding found in libsrp.

Note that  @code{b64_data} should be null terminated.

Warning!  This base64 encoding is not the "standard" encoding, so
do not use it for non-SRP purposes.

@strong{Returns:} @code{GNUTLS_E_SHORT_MEMORY_BUFFER}  if the buffer given is not
long enough, or 0 on success.
@end deftypefun

@subheading gnutls_srp_base64_decode2
@anchor{gnutls_srp_base64_decode2}
@deftypefun {int} {gnutls_srp_base64_decode2} (const gnutls_datum_t * @var{b64_data}, gnutls_datum_t * @var{result})
@var{b64_data}: contains the encoded data

@var{result}: the place where decoded data lie

This function will decode the given encoded data. The decoded data
will be allocated, and stored into result.  It will decode using
the base64 algorithm as used in libsrp.

You should use @code{gnutls_free()}  to free the returned data.

Warning!  This base64 encoding is not the "standard" encoding, so
do not use it for non-SRP purposes.

@strong{Returns:} 0 on success, or an error code.
@end deftypefun

@subheading gnutls_srp_base64_encode
@anchor{gnutls_srp_base64_encode}
@deftypefun {int} {gnutls_srp_base64_encode} (const gnutls_datum_t * @var{data}, char * @var{result}, size_t * @var{result_size})
@var{data}: contain the raw data

@var{result}: the place where base64 data will be copied

@var{result_size}: holds the size of the result

This function will convert the given data to printable data, using
the base64 encoding, as used in the libsrp.  This is the encoding
used in SRP password files.  If the provided buffer is not long
enough GNUTLS_E_SHORT_MEMORY_BUFFER is returned.

Warning!  This base64 encoding is not the "standard" encoding, so
do not use it for non-SRP purposes.

@strong{Returns:} @code{GNUTLS_E_SHORT_MEMORY_BUFFER}  if the buffer given is not
long enough, or 0 on success.
@end deftypefun

@subheading gnutls_srp_base64_encode2
@anchor{gnutls_srp_base64_encode2}
@deftypefun {int} {gnutls_srp_base64_encode2} (const gnutls_datum_t * @var{data}, gnutls_datum_t * @var{result})
@var{data}: contains the raw data

@var{result}: will hold the newly allocated encoded data

This function will convert the given data to printable data, using
the base64 encoding.  This is the encoding used in SRP password
files.  This function will allocate the required memory to hold
the encoded data.

You should use @code{gnutls_free()}  to free the returned data.

Warning!  This base64 encoding is not the "standard" encoding, so
do not use it for non-SRP purposes.

@strong{Returns:} 0 on success, or an error code.
@end deftypefun

@subheading gnutls_srp_free_client_credentials
@anchor{gnutls_srp_free_client_credentials}
@deftypefun {void} {gnutls_srp_free_client_credentials} (gnutls_srp_client_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_srp_client_credentials_t}  type.

Free a gnutls_srp_client_credentials_t structure.
@end deftypefun

@subheading gnutls_srp_free_server_credentials
@anchor{gnutls_srp_free_server_credentials}
@deftypefun {void} {gnutls_srp_free_server_credentials} (gnutls_srp_server_credentials_t @var{sc})
@var{sc}: is a @code{gnutls_srp_server_credentials_t}  type.

Free a gnutls_srp_server_credentials_t structure.
@end deftypefun

@subheading gnutls_srp_server_get_username
@anchor{gnutls_srp_server_get_username}
@deftypefun {const char *} {gnutls_srp_server_get_username} (gnutls_session_t @var{session})
@var{session}: is a gnutls session

This function will return the username of the peer.  This should
only be called in case of SRP authentication and in case of a
server.  Returns NULL in case of an error.

@strong{Returns:} SRP username of the peer, or NULL in case of error.
@end deftypefun

@subheading gnutls_srp_set_client_credentials
@anchor{gnutls_srp_set_client_credentials}
@deftypefun {int} {gnutls_srp_set_client_credentials} (gnutls_srp_client_credentials_t @var{res}, const char * @var{username}, const char * @var{password})
@var{res}: is a @code{gnutls_srp_client_credentials_t}  type.

@var{username}: is the user's userid

@var{password}: is the user's password

This function sets the username and password, in a
@code{gnutls_srp_client_credentials_t}  type.  Those will be used in
SRP authentication.   @code{username} should be an ASCII string or UTF-8
string. In case of a UTF-8 string it is recommended to be following
the PRECIS framework for usernames (rfc8265). The password can
be in ASCII format, or normalized using @code{gnutls_utf8_password_normalize()} .

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, or an
error code.
@end deftypefun

@subheading gnutls_srp_set_client_credentials_function
@anchor{gnutls_srp_set_client_credentials_function}
@deftypefun {void} {gnutls_srp_set_client_credentials_function} (gnutls_srp_client_credentials_t         @var{cred}, gnutls_srp_client_credentials_function         * @var{func})
@var{cred}: is a @code{gnutls_srp_server_credentials_t}  type.

@var{func}: is the callback function

This function can be used to set a callback to retrieve the
username and password for client SRP authentication.  The
callback's function form is:

int (*callback)(gnutls_session_t, char** username, char**password);

The  @code{username} and  @code{password} must be allocated using
@code{gnutls_malloc()} .

The  @code{username} should be an ASCII string or UTF-8
string. In case of a UTF-8 string it is recommended to be following
the PRECIS framework for usernames (rfc8265). The password can
be in ASCII format, or normalized using @code{gnutls_utf8_password_normalize()} .

The callback function will be called once per handshake before the
initial hello message is sent.

The callback should not return a negative error code the second
time called, since the handshake procedure will be aborted.

The callback function should return 0 on success.
-1 indicates an error.
@end deftypefun

@subheading gnutls_srp_set_prime_bits
@anchor{gnutls_srp_set_prime_bits}
@deftypefun {void} {gnutls_srp_set_prime_bits} (gnutls_session_t @var{session}, unsigned int @var{bits})
@var{session}: is a @code{gnutls_session_t}  type.

@var{bits}: is the number of bits

This function sets the minimum accepted number of bits, for use in
an SRP key exchange.  If zero, the default 2048 bits will be used.

In the client side it sets the minimum accepted number of bits.  If
a server sends a prime with less bits than that
@code{GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER}  will be returned by the
handshake.

This function has no effect in server side.

@strong{Since:} 2.6.0
@end deftypefun

@subheading gnutls_srp_set_server_credentials_file
@anchor{gnutls_srp_set_server_credentials_file}
@deftypefun {int} {gnutls_srp_set_server_credentials_file} (gnutls_srp_server_credentials_t @var{res}, const char * @var{password_file}, const char * @var{password_conf_file})
@var{res}: is a @code{gnutls_srp_server_credentials_t}  type.

@var{password_file}: is the SRP password file (tpasswd)

@var{password_conf_file}: is the SRP password conf file (tpasswd.conf)

This function sets the password files, in a
@code{gnutls_srp_server_credentials_t}  type.  Those password files
hold usernames and verifiers and will be used for SRP
authentication.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, or an
error code.
@end deftypefun

@subheading gnutls_srp_set_server_credentials_function
@anchor{gnutls_srp_set_server_credentials_function}
@deftypefun {void} {gnutls_srp_set_server_credentials_function} (gnutls_srp_server_credentials_t         @var{cred}, gnutls_srp_server_credentials_function         * @var{func})
@var{cred}: is a @code{gnutls_srp_server_credentials_t}  type.

@var{func}: is the callback function

This function can be used to set a callback to retrieve the user's
SRP credentials.  The callback's function form is:

int (*callback)(gnutls_session_t, const char* username,
gnutls_datum_t *salt, gnutls_datum_t *verifier, gnutls_datum_t *generator,
gnutls_datum_t *prime);

 @code{username} contains the actual username.
The  @code{salt} ,  @code{verifier} ,  @code{generator} and  @code{prime} must be filled
in using the @code{gnutls_malloc()} . For convenience  @code{prime} and  @code{generator} may also be one of the static parameters defined in gnutls.h.

Initially, the data field is NULL in every @code{gnutls_datum_t} 
structure that the callback has to fill in. When the
callback is done GnuTLS deallocates all of those buffers
which are non-NULL, regardless of the return value.

In order to prevent attackers from guessing valid usernames,
if a user does not exist, g and n values should be filled in
using a random user's parameters. In that case the callback must
return the special value (1).
See @code{gnutls_srp_set_server_fake_salt_seed}  too.
If this is not required for your application, return a negative
number from the callback to abort the handshake.

The callback function will only be called once per handshake.
The callback function should return 0 on success, while
-1 indicates an error.
@end deftypefun

@subheading gnutls_srp_set_server_fake_salt_seed
@anchor{gnutls_srp_set_server_fake_salt_seed}
@deftypefun {void} {gnutls_srp_set_server_fake_salt_seed} (gnutls_srp_server_credentials_t @var{cred}, const gnutls_datum_t * @var{seed}, unsigned int @var{salt_length})
@var{cred}: is a @code{gnutls_srp_server_credentials_t}  type

@var{seed}: is the seed data, only needs to be valid until the function
returns; size of the seed must be greater than zero

@var{salt_length}: is the length of the generated fake salts

This function sets the seed that is used to generate salts for
invalid (non-existent) usernames.

In order to prevent attackers from guessing valid usernames,
when a user does not exist gnutls generates a salt and a verifier
and proceeds with the protocol as usual.
The authentication will ultimately fail, but the client cannot tell
whether the username is valid (exists) or invalid.

If an attacker learns the seed, given a salt (which is part of the
handshake) which was generated when the seed was in use, it can tell
whether or not the authentication failed because of an unknown username.
This seed cannot be used to reveal application data or passwords.

 @code{salt_length} should represent the salt length your application uses.
Generating fake salts longer than 20 bytes is not supported.

By default the seed is a random value, different each time a
@code{gnutls_srp_server_credentials_t}  is allocated and fake salts are
16 bytes long.

@strong{Since:} 3.3.0
@end deftypefun

@subheading gnutls_srp_verifier
@anchor{gnutls_srp_verifier}
@deftypefun {int} {gnutls_srp_verifier} (const char * @var{username}, const char * @var{password}, const gnutls_datum_t * @var{salt}, const gnutls_datum_t * @var{generator}, const gnutls_datum_t * @var{prime}, gnutls_datum_t * @var{res})
@var{username}: is the user's name

@var{password}: is the user's password

@var{salt}: should be some randomly generated bytes

@var{generator}: is the generator of the group

@var{prime}: is the group's prime

@var{res}: where the verifier will be stored.

This function will create an SRP verifier, as specified in
RFC2945.  The  @code{prime} and  @code{generator} should be one of the static
parameters defined in gnutls/gnutls.h or may be generated.

The verifier will be allocated with  @code{gnutls_malloc} () and will be stored in
 @code{res} using binary format.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, or an
error code.
@end deftypefun

@subheading gnutls_srtp_get_keys
@anchor{gnutls_srtp_get_keys}
@deftypefun {int} {gnutls_srtp_get_keys} (gnutls_session_t @var{session}, void * @var{key_material}, unsigned int @var{key_material_size}, gnutls_datum_t * @var{client_key}, gnutls_datum_t * @var{client_salt}, gnutls_datum_t * @var{server_key}, gnutls_datum_t * @var{server_salt})
@var{session}: is a @code{gnutls_session_t}  type.

@var{key_material}: Space to hold the generated key material

@var{key_material_size}: The maximum size of the key material

@var{client_key}: The master client write key, pointing inside the key material

@var{client_salt}: The master client write salt, pointing inside the key material

@var{server_key}: The master server write key, pointing inside the key material

@var{server_salt}: The master server write salt, pointing inside the key material

This is a helper function to generate the keying material for SRTP.
It requires the space of the key material to be pre-allocated (should be at least
2x the maximum key size and salt size). The  @code{client_key} ,  @code{client_salt} ,  @code{server_key} and  @code{server_salt} are convenience datums that point inside the key material. They may
be @code{NULL} .

@strong{Returns:} On success the size of the key material is returned,
otherwise, @code{GNUTLS_E_SHORT_MEMORY_BUFFER}  if the buffer given is not 
sufficient, or a negative error code.

Since 3.1.4
@end deftypefun

@subheading gnutls_srtp_get_mki
@anchor{gnutls_srtp_get_mki}
@deftypefun {int} {gnutls_srtp_get_mki} (gnutls_session_t @var{session}, gnutls_datum_t * @var{mki})
@var{session}: is a @code{gnutls_session_t}  type.

@var{mki}: will hold the MKI

This function exports the negotiated Master Key Identifier,
received by the peer if any. The returned value in  @code{mki} should be 
treated as constant and valid only during the session's lifetime.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

Since 3.1.4
@end deftypefun

@subheading gnutls_srtp_get_profile_id
@anchor{gnutls_srtp_get_profile_id}
@deftypefun {int} {gnutls_srtp_get_profile_id} (const char * @var{name}, gnutls_srtp_profile_t * @var{profile})
@var{name}: The name of the profile to look up

@var{profile}: Will hold the profile id

This function allows you to look up a profile based on a string.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

Since 3.1.4
@end deftypefun

@subheading gnutls_srtp_get_profile_name
@anchor{gnutls_srtp_get_profile_name}
@deftypefun {const char *} {gnutls_srtp_get_profile_name} (gnutls_srtp_profile_t @var{profile})
@var{profile}: The profile to look up a string for

This function allows you to get the corresponding name for a
SRTP protection profile.

@strong{Returns:} On success, the name of a SRTP profile as a string,
otherwise NULL.

Since 3.1.4
@end deftypefun

@subheading gnutls_srtp_get_selected_profile
@anchor{gnutls_srtp_get_selected_profile}
@deftypefun {int} {gnutls_srtp_get_selected_profile} (gnutls_session_t @var{session}, gnutls_srtp_profile_t * @var{profile})
@var{session}: is a @code{gnutls_session_t}  type.

@var{profile}: will hold the profile

This function allows you to get the negotiated SRTP profile.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

Since 3.1.4
@end deftypefun

@subheading gnutls_srtp_set_mki
@anchor{gnutls_srtp_set_mki}
@deftypefun {int} {gnutls_srtp_set_mki} (gnutls_session_t @var{session}, const gnutls_datum_t * @var{mki})
@var{session}: is a @code{gnutls_session_t}  type.

@var{mki}: holds the MKI

This function sets the Master Key Identifier, to be
used by this session (if any).

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

Since 3.1.4
@end deftypefun

@subheading gnutls_srtp_set_profile
@anchor{gnutls_srtp_set_profile}
@deftypefun {int} {gnutls_srtp_set_profile} (gnutls_session_t @var{session}, gnutls_srtp_profile_t @var{profile})
@var{session}: is a @code{gnutls_session_t}  type.

@var{profile}: is the profile id to add.

This function is to be used by both clients and servers, to declare
what SRTP profiles they support, to negotiate with the peer.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
otherwise a negative error code is returned.

Since 3.1.4
@end deftypefun

@subheading gnutls_srtp_set_profile_direct
@anchor{gnutls_srtp_set_profile_direct}
@deftypefun {int} {gnutls_srtp_set_profile_direct} (gnutls_session_t @var{session}, const char * @var{profiles}, const char ** @var{err_pos})
@var{session}: is a @code{gnutls_session_t}  type.

@var{profiles}: is a string that contains the supported SRTP profiles,
separated by colons.

@var{err_pos}: In case of an error this will have the position in the string the error occurred, may be NULL.

This function is to be used by both clients and servers, to declare
what SRTP profiles they support, to negotiate with the peer.

@strong{Returns:} On syntax error @code{GNUTLS_E_INVALID_REQUEST}  is returned,
@code{GNUTLS_E_SUCCESS}  on success, or an error code.

Since 3.1.4
@end deftypefun

@subheading gnutls_store_commitment
@anchor{gnutls_store_commitment}
@deftypefun {int} {gnutls_store_commitment} (const char * @var{db_name}, gnutls_tdb_t @var{tdb}, const char * @var{host}, const char * @var{service}, gnutls_digest_algorithm_t @var{hash_algo}, const gnutls_datum_t * @var{hash}, time_t @var{expiration}, unsigned int @var{flags})
@var{db_name}: A file specifying the stored keys (use NULL for the default)

@var{tdb}: A storage structure or NULL to use the default

@var{host}: The peer's name

@var{service}: non-NULL if this key is specific to a service (e.g. http)

@var{hash_algo}: The hash algorithm type

@var{hash}: The raw hash

@var{expiration}: The expiration time (use 0 to disable expiration)

@var{flags}: should be 0 or @code{GNUTLS_SCOMMIT_FLAG_ALLOW_BROKEN} .

This function will store the provided hash commitment to
the list of stored public keys. The key with the given
hash will be considered valid until the provided expiration time.

The  @code{tdb} variable if non-null specifies a custom backend for
the storage of entries. If it is NULL then the
default file backend will be used.

Note that this function is not thread safe with the default backend.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a
negative error value.

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_store_pubkey
@anchor{gnutls_store_pubkey}
@deftypefun {int} {gnutls_store_pubkey} (const char * @var{db_name}, gnutls_tdb_t @var{tdb}, const char * @var{host}, const char * @var{service}, gnutls_certificate_type_t @var{cert_type}, const gnutls_datum_t * @var{cert}, time_t @var{expiration}, unsigned int @var{flags})
@var{db_name}: A file specifying the stored keys (use NULL for the default)

@var{tdb}: A storage structure or NULL to use the default

@var{host}: The peer's name

@var{service}: non-NULL if this key is specific to a service (e.g. http)

@var{cert_type}: The type of the certificate

@var{cert}: The data of the certificate

@var{expiration}: The expiration time (use 0 to disable expiration)

@var{flags}: should be 0.

This function will store a raw public-key or a public-key provided via
a raw (DER-encoded) certificate to the list of stored public keys. The key
will be considered valid until the provided expiration time.

The  @code{tdb} variable if non-null specifies a custom backend for
the storage of entries. If it is NULL then the
default file backend will be used.

Unless an alternative  @code{tdb} is provided, the storage format is a textual format
consisting of a line for each host with fields separated by '|'. The contents of
the fields are a format-identifier which is set to 'g0', the hostname that the
rest of the data applies to, the numeric port or host name, the expiration
time in seconds since the epoch (0 for no expiration), and a base64
encoding of the raw (DER) public key information (SPKI) of the peer.

As of GnuTLS 3.6.6 this function also accepts raw public keys.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a
negative error value.

@strong{Since:} 3.0.13
@end deftypefun

@subheading gnutls_strerror
@anchor{gnutls_strerror}
@deftypefun {const char *} {gnutls_strerror} (int @var{error})
@var{error}: is a GnuTLS error code, a negative error code

This function is similar to strerror.  The difference is that it
accepts an error number returned by a gnutls function; In case of
an unknown error a descriptive string is sent instead of @code{NULL} .

Error codes are always a negative error code.

@strong{Returns:} A string explaining the GnuTLS error message.
@end deftypefun

@subheading gnutls_strerror_name
@anchor{gnutls_strerror_name}
@deftypefun {const char *} {gnutls_strerror_name} (int @var{error})
@var{error}: is an error returned by a gnutls function.

Return the GnuTLS error code define as a string.  For example,
gnutls_strerror_name (GNUTLS_E_DH_PRIME_UNACCEPTABLE) will return
the string "GNUTLS_E_DH_PRIME_UNACCEPTABLE".

@strong{Returns:} A string corresponding to the symbol name of the error
code.

@strong{Since:} 2.6.0
@end deftypefun

@subheading gnutls_supplemental_get_name
@anchor{gnutls_supplemental_get_name}
@deftypefun {const char     *} {gnutls_supplemental_get_name} (gnutls_supplemental_data_format_type_t       @var{type})
@var{type}: is a supplemental data format type

Convert a @code{gnutls_supplemental_data_format_type_t}  value to a
string.

@strong{Returns:} a string that contains the name of the specified
supplemental data format type, or @code{NULL}  for unknown types.
@end deftypefun

@subheading gnutls_supplemental_recv
@anchor{gnutls_supplemental_recv}
@deftypefun {void} {gnutls_supplemental_recv} (gnutls_session_t @var{session}, unsigned @var{do_recv_supplemental})
@var{session}: is a @code{gnutls_session_t}  type.

@var{do_recv_supplemental}: non-zero in order to expect supplemental data

This function is to be called by an extension handler to
instruct gnutls to attempt to receive supplemental data
during the handshake process.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_supplemental_register
@anchor{gnutls_supplemental_register}
@deftypefun {int} {gnutls_supplemental_register} (const char * @var{name}, gnutls_supplemental_data_format_type_t @var{type}, gnutls_supp_recv_func @var{recv_func}, gnutls_supp_send_func @var{send_func})
@var{name}: the name of the supplemental data to register

@var{type}: the type of the supplemental data format

@var{recv_func}: the function to receive the data

@var{send_func}: the function to send the data

This function will register a new supplemental data type (rfc4680).
The registered data will remain until @code{gnutls_global_deinit()} 
is called. The provided  @code{type} must be an unassigned type in
@code{gnutls_supplemental_data_format_type_t} . If the type is already
registered or handled by GnuTLS internally @code{GNUTLS_E_ALREADY_REGISTERED} 
will be returned.

This function is not thread safe. As supplemental data are not defined under
TLS 1.3, this function will disable TLS 1.3 support globally.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_supplemental_send
@anchor{gnutls_supplemental_send}
@deftypefun {void} {gnutls_supplemental_send} (gnutls_session_t @var{session}, unsigned @var{do_send_supplemental})
@var{session}: is a @code{gnutls_session_t}  type.

@var{do_send_supplemental}: non-zero in order to send supplemental data

This function is to be called by an extension handler to
instruct gnutls to send supplemental data during the handshake process.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_system_recv_timeout
@anchor{gnutls_system_recv_timeout}
@deftypefun {int} {gnutls_system_recv_timeout} (gnutls_transport_ptr_t @var{ptr}, unsigned int @var{ms})
@var{ptr}: A file descriptor (wrapped in a gnutls_transport_ptr_t pointer)

@var{ms}: The number of milliseconds to wait.

Wait for data to be received from the provided socket ( @code{ptr} ) within a
timeout period in milliseconds, using @code{select()}  on the provided  @code{ptr} .

This function is provided as a helper for constructing custom
callbacks for @code{gnutls_transport_set_pull_timeout_function()} ,
which can be used if you rely on socket file descriptors.

Returns -1 on error, 0 on timeout, positive value if data are available for reading.

@strong{Since:} 3.4.0
@end deftypefun

@subheading gnutls_tdb_deinit
@anchor{gnutls_tdb_deinit}
@deftypefun {void} {gnutls_tdb_deinit} (gnutls_tdb_t @var{tdb})
@var{tdb}: The structure to be deinitialized

This function will deinitialize a public key trust storage structure.
@end deftypefun

@subheading gnutls_tdb_init
@anchor{gnutls_tdb_init}
@deftypefun {int} {gnutls_tdb_init} (gnutls_tdb_t * @var{tdb})
@var{tdb}: A pointer to the type to be initialized

This function will initialize a public key trust storage structure.

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise a
negative error value.
@end deftypefun

@subheading gnutls_tdb_set_store_commitment_func
@anchor{gnutls_tdb_set_store_commitment_func}
@deftypefun {void} {gnutls_tdb_set_store_commitment_func} (gnutls_tdb_t @var{tdb}, gnutls_tdb_store_commitment_func        @var{cstore})
@var{tdb}: The trust storage

@var{cstore}: The commitment storage function

This function will associate a commitment (hash) storage function with the
trust storage structure. The function is of the following form.

int gnutls_tdb_store_commitment_func(const char* db_name, const char* host,
const char* service, time_t expiration,
gnutls_digest_algorithm_t, const gnutls_datum_t* hash);

The  @code{db_name} should be used to pass any private data to this function.
@end deftypefun

@subheading gnutls_tdb_set_store_func
@anchor{gnutls_tdb_set_store_func}
@deftypefun {void} {gnutls_tdb_set_store_func} (gnutls_tdb_t @var{tdb}, gnutls_tdb_store_func @var{store})
@var{tdb}: The trust storage

@var{store}: The storage function

This function will associate a storage function with the
trust storage structure. The function is of the following form.

int gnutls_tdb_store_func(const char* db_name, const char* host,
const char* service, time_t expiration,
const gnutls_datum_t* pubkey);

The  @code{db_name} should be used to pass any private data to this function.
@end deftypefun

@subheading gnutls_tdb_set_verify_func
@anchor{gnutls_tdb_set_verify_func}
@deftypefun {void} {gnutls_tdb_set_verify_func} (gnutls_tdb_t @var{tdb}, gnutls_tdb_verify_func @var{verify})
@var{tdb}: The trust storage

@var{verify}: The verification function

This function will associate a retrieval function with the
trust storage structure. The function is of the following form.

int gnutls_tdb_verify_func(const char* db_name, const char* host,
const char* service, const gnutls_datum_t* pubkey);

The verify function should return zero on a match, @code{GNUTLS_E_CERTIFICATE_KEY_MISMATCH} 
if there is a mismatch and any other negative error code otherwise.

The  @code{db_name} should be used to pass any private data to this function.
@end deftypefun

@subheading gnutls_transport_get_int
@anchor{gnutls_transport_get_int}
@deftypefun {int} {gnutls_transport_get_int} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Used to get the first argument of the transport function (like
PUSH and PULL).  This must have been set using
@code{gnutls_transport_set_int()} .

@strong{Returns:} The first argument of the transport function.

@strong{Since:} 3.1.9
@end deftypefun

@subheading gnutls_transport_get_int2
@anchor{gnutls_transport_get_int2}
@deftypefun {void} {gnutls_transport_get_int2} (gnutls_session_t @var{session}, int * @var{recv_int}, int * @var{send_int})
@var{session}: is a @code{gnutls_session_t}  type.

@var{recv_int}: will hold the value for the pull function

@var{send_int}: will hold the value for the push function

Used to get the arguments of the transport functions (like PUSH
and PULL).  These should have been set using
@code{gnutls_transport_set_int2()} .

@strong{Since:} 3.1.9
@end deftypefun

@subheading gnutls_transport_get_ptr
@anchor{gnutls_transport_get_ptr}
@deftypefun {gnutls_transport_ptr_t} {gnutls_transport_get_ptr} (gnutls_session_t @var{session})
@var{session}: is a @code{gnutls_session_t}  type.

Used to get the first argument of the transport function (like
PUSH and PULL).  This must have been set using
@code{gnutls_transport_set_ptr()} .

@strong{Returns:} The first argument of the transport function.
@end deftypefun

@subheading gnutls_transport_get_ptr2
@anchor{gnutls_transport_get_ptr2}
@deftypefun {void} {gnutls_transport_get_ptr2} (gnutls_session_t @var{session}, gnutls_transport_ptr_t * @var{recv_ptr}, gnutls_transport_ptr_t * @var{send_ptr})
@var{session}: is a @code{gnutls_session_t}  type.

@var{recv_ptr}: will hold the value for the pull function

@var{send_ptr}: will hold the value for the push function

Used to get the arguments of the transport functions (like PUSH
and PULL).  These should have been set using
@code{gnutls_transport_set_ptr2()} .
@end deftypefun

@subheading gnutls_transport_set_errno
@anchor{gnutls_transport_set_errno}
@deftypefun {void} {gnutls_transport_set_errno} (gnutls_session_t @var{session}, int @var{err})
@var{session}: is a @code{gnutls_session_t}  type.

@var{err}: error value to store in session-specific errno variable.

Store  @code{err} in the session-specific errno variable.  Useful values
for  @code{err} are EINTR, EAGAIN and EMSGSIZE, other values are treated will be
treated as real errors in the push/pull function.

This function is useful in replacement push and pull functions set by
@code{gnutls_transport_set_push_function()}  and
@code{gnutls_transport_set_pull_function()}  under Windows, where the
replacements may not have access to the same  @code{errno} variable that is used by GnuTLS (e.g., the application is linked to
msvcr71.dll and gnutls is linked to msvcrt.dll).

This function is unreliable if you are using the same
 @code{session} in different threads for sending and receiving.
@end deftypefun

@subheading gnutls_transport_set_errno_function
@anchor{gnutls_transport_set_errno_function}
@deftypefun {void} {gnutls_transport_set_errno_function} (gnutls_session_t @var{session}, gnutls_errno_func @var{errno_func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{errno_func}: a callback function similar to @code{write()} 

This is the function where you set a function to retrieve errno
after a failed push or pull operation.

 @code{errno_func} is of the form,
int (*gnutls_errno_func)(gnutls_transport_ptr_t);
and should return the errno.

@strong{Since:} 2.12.0
@end deftypefun

@subheading gnutls_transport_set_int
@anchor{gnutls_transport_set_int}
@deftypefun {void} {gnutls_transport_set_int} (gnutls_session_t @var{session}, int @var{fd})
@var{session}: is a @code{gnutls_session_t}  type.

@var{fd}: is the socket descriptor for the connection.

This function sets the first argument of the transport function, such
as @code{send()}  and @code{recv()}  for the default callbacks using the
system's socket API.

This function is equivalent to calling @code{gnutls_transport_set_ptr()} 
with the descriptor, but requires no casts.

@strong{Since:} 3.1.9
@end deftypefun

@subheading gnutls_transport_set_int2
@anchor{gnutls_transport_set_int2}
@deftypefun {void} {gnutls_transport_set_int2} (gnutls_session_t @var{session}, int @var{recv_fd}, int @var{send_fd})
@var{session}: is a @code{gnutls_session_t}  type.

@var{recv_fd}: is socket descriptor for the pull function

@var{send_fd}: is socket descriptor for the push function

This function sets the first argument of the transport functions,
such as @code{send()}  and @code{recv()}  for the default callbacks using the
system's socket API. With this function you can set two different
descriptors for receiving and sending.

This function is equivalent to calling @code{gnutls_transport_set_ptr2()} 
with the descriptors, but requires no casts.

@strong{Since:} 3.1.9
@end deftypefun

@subheading gnutls_transport_set_ptr
@anchor{gnutls_transport_set_ptr}
@deftypefun {void} {gnutls_transport_set_ptr} (gnutls_session_t @var{session}, gnutls_transport_ptr_t @var{ptr})
@var{session}: is a @code{gnutls_session_t}  type.

@var{ptr}: is the value.

Used to set the first argument of the transport function (for push
and pull callbacks). In berkeley style sockets this function will set the
connection descriptor.
@end deftypefun

@subheading gnutls_transport_set_ptr2
@anchor{gnutls_transport_set_ptr2}
@deftypefun {void} {gnutls_transport_set_ptr2} (gnutls_session_t @var{session}, gnutls_transport_ptr_t @var{recv_ptr}, gnutls_transport_ptr_t @var{send_ptr})
@var{session}: is a @code{gnutls_session_t}  type.

@var{recv_ptr}: is the value for the pull function

@var{send_ptr}: is the value for the push function

Used to set the first argument of the transport function (for push
and pull callbacks). In berkeley style sockets this function will set the
connection descriptor.  With this function you can use two different
pointers for receiving and sending.
@end deftypefun

@subheading gnutls_transport_set_pull_function
@anchor{gnutls_transport_set_pull_function}
@deftypefun {void} {gnutls_transport_set_pull_function} (gnutls_session_t @var{session}, gnutls_pull_func @var{pull_func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{pull_func}: a callback function similar to @code{read()} 

This is the function where you set a function for gnutls to receive
data.  Normally, if you use berkeley style sockets, do not need to
use this function since the default recv(2) will probably be ok.
The callback should return 0 on connection termination, a positive
number indicating the number of bytes received, and -1 on error.

 @code{gnutls_pull_func} is of the form,
ssize_t (*gnutls_pull_func)(gnutls_transport_ptr_t, void*, size_t);
@end deftypefun

@subheading gnutls_transport_set_pull_timeout_function
@anchor{gnutls_transport_set_pull_timeout_function}
@deftypefun {void} {gnutls_transport_set_pull_timeout_function} (gnutls_session_t @var{session}, gnutls_pull_timeout_func @var{func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{func}: a callback function

This is the function where you set a function for gnutls to know
whether data are ready to be received. It should wait for data a
given time frame in milliseconds. The callback should return 0 on 
timeout, a positive number if data can be received, and -1 on error.
You'll need to override this function if @code{select()}  is not suitable
for the provided transport calls.

As with @code{select()} , if the timeout value is zero the callback should return
zero if no data are immediately available. The special value
@code{GNUTLS_INDEFINITE_TIMEOUT}  indicates that the callback should wait indefinitely
for data.

 @code{gnutls_pull_timeout_func} is of the form,
int (*gnutls_pull_timeout_func)(gnutls_transport_ptr_t, unsigned int ms);

This callback is necessary when @code{gnutls_handshake_set_timeout()}  or 
@code{gnutls_record_set_timeout()}  are set, under TLS1.3 and for enforcing the DTLS
mode timeouts when in blocking mode.

For compatibility with future GnuTLS versions this callback must be set when
a custom pull function is registered. The callback will not be used when the
session is in TLS mode with non-blocking sockets. That is, when @code{GNUTLS_NONBLOCK} 
is specified for a TLS session in @code{gnutls_init()} .

The helper function @code{gnutls_system_recv_timeout()}  is provided to
simplify writing callbacks. 

@strong{Since:} 3.0
@end deftypefun

@subheading gnutls_transport_set_push_function
@anchor{gnutls_transport_set_push_function}
@deftypefun {void} {gnutls_transport_set_push_function} (gnutls_session_t @var{session}, gnutls_push_func @var{push_func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{push_func}: a callback function similar to @code{write()} 

This is the function where you set a push function for gnutls to
use in order to send data.  If you are going to use berkeley style
sockets, you do not need to use this function since the default
send(2) will probably be ok.  Otherwise you should specify this
function for gnutls to be able to send data.
The callback should return a positive number indicating the
bytes sent, and -1 on error.

 @code{push_func} is of the form,
ssize_t (*gnutls_push_func)(gnutls_transport_ptr_t, const void*, size_t);
@end deftypefun

@subheading gnutls_transport_set_vec_push_function
@anchor{gnutls_transport_set_vec_push_function}
@deftypefun {void} {gnutls_transport_set_vec_push_function} (gnutls_session_t @var{session}, gnutls_vec_push_func @var{vec_func})
@var{session}: is a @code{gnutls_session_t}  type.

@var{vec_func}: a callback function similar to @code{writev()} 

Using this function you can override the default writev(2)
function for gnutls to send data. Setting this callback 
instead of @code{gnutls_transport_set_push_function()}  is recommended
since it introduces less overhead in the TLS handshake process.

 @code{vec_func} is of the form,
ssize_t (*gnutls_vec_push_func) (gnutls_transport_ptr_t, const giovec_t * iov, int iovcnt);

@strong{Since:} 2.12.0
@end deftypefun

@subheading gnutls_url_is_supported
@anchor{gnutls_url_is_supported}
@deftypefun {unsigned} {gnutls_url_is_supported} (const char * @var{url})
@var{url}: A URI to be tested

Check whether the provided  @code{url} is supported.  Depending on the system libraries
GnuTLS may support pkcs11, tpmkey or other URLs.

@strong{Returns:} return non-zero if the given URL is supported, and zero if
it is not known.

@strong{Since:} 3.1.0
@end deftypefun

@subheading gnutls_utf8_password_normalize
@anchor{gnutls_utf8_password_normalize}
@deftypefun {int} {gnutls_utf8_password_normalize} (const unsigned char * @var{password}, unsigned @var{plen}, gnutls_datum_t * @var{out}, unsigned @var{flags})
@var{password}: contain the UTF-8 formatted password

@var{plen}: the length of the provided password

@var{out}: the result in an null-terminated allocated string

@var{flags}: should be zero

This function will convert the provided UTF-8 password according
to the normalization rules in RFC7613.

If the flag @code{GNUTLS_UTF8_IGNORE_ERRS}  is specified, any UTF-8 encoding
errors will be ignored, and in that case the output will be a copy of the input.

@strong{Returns:} @code{GNUTLS_E_INVALID_UTF8_STRING}  on invalid UTF-8 data, or 0 on success.

@strong{Since:} 3.5.7
@end deftypefun

@subheading gnutls_verify_stored_pubkey
@anchor{gnutls_verify_stored_pubkey}
@deftypefun {int} {gnutls_verify_stored_pubkey} (const char * @var{db_name}, gnutls_tdb_t @var{tdb}, const char * @var{host}, const char * @var{service}, gnutls_certificate_type_t @var{cert_type}, const gnutls_datum_t * @var{cert}, unsigned int @var{flags})
@var{db_name}: A file specifying the stored keys (use NULL for the default)

@var{tdb}: A storage structure or NULL to use the default

@var{host}: The peer's name

@var{service}: non-NULL if this key is specific to a service (e.g. http)

@var{cert_type}: The type of the certificate

@var{cert}: The raw (der) data of the certificate

@var{flags}: should be 0.

This function will try to verify a raw public-key or a public-key provided via
a raw (DER-encoded) certificate using a list of stored public keys.
The  @code{service} field if non-NULL should be a port number.

The  @code{db_name} variable if non-null specifies a custom backend for
the retrieval of entries. If it is NULL then the
default file backend will be used. In POSIX-like systems the
file backend uses the $HOME/.gnutls/known_hosts file.

Note that if the custom storage backend is provided the
retrieval function should return @code{GNUTLS_E_CERTIFICATE_KEY_MISMATCH} 
if the host/service pair is found but key doesn't match,
@code{GNUTLS_E_NO_CERTIFICATE_FOUND}  if no such host/service with
the given key is found, and 0 if it was found. The storage
function should return 0 on success.

As of GnuTLS 3.6.6 this function also verifies raw public keys.

@strong{Returns:} If no associated public key is found
then @code{GNUTLS_E_NO_CERTIFICATE_FOUND}  will be returned. If a key
is found but does not match @code{GNUTLS_E_CERTIFICATE_KEY_MISMATCH} 
is returned. On success, @code{GNUTLS_E_SUCCESS}  (0) is returned,
or a negative error value on other errors.

@strong{Since:} 3.0.13
@end deftypefun