path: root/man/man8/tlsproxy.8

.TH TLSPROXY 8 
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.SH NAME
tlsproxy
\-
Postfix TLS proxy
.SH "SYNOPSIS"
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\fBtlsproxy\fR [generic Postfix daemon options]
.SH DESCRIPTION
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The \fBtlsproxy\fR(8) server implements a two\-way TLS proxy. It
is used by the \fBpostscreen\fR(8) server to talk SMTP\-over\-TLS
with remote SMTP clients that are not allowlisted (including
clients whose allowlist status has expired), and by the
\fBsmtp\fR(8) client to support TLS connection reuse, but it
should also work for non\-SMTP protocols.

Although one \fBtlsproxy\fR(8) process can serve multiple
sessions at the same time, it is a good idea to allow the
number of processes to increase with load, so that the
service remains responsive.
.SH "PROTOCOL EXAMPLE"
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The example below concerns \fBpostscreen\fR(8). However,
the \fBtlsproxy\fR(8) server is agnostic of the application
protocol, and the example is easily adapted to other
applications.

After receiving a valid remote SMTP client STARTTLS command,
the \fBpostscreen\fR(8) server sends the remote SMTP client
endpoint string, the requested role (server), and the
requested timeout to \fBtlsproxy\fR(8).  \fBpostscreen\fR(8)
then receives a "TLS available" indication from \fBtlsproxy\fR(8).
If the TLS service is available, \fBpostscreen\fR(8) sends
the remote SMTP client file descriptor to \fBtlsproxy\fR(8),
and sends the plaintext 220 greeting to the remote SMTP
client.  This triggers TLS negotiations between the remote
SMTP client and \fBtlsproxy\fR(8).  Upon completion of the
TLS\-level handshake, \fBtlsproxy\fR(8) translates between
plaintext from/to \fBpostscreen\fR(8) and ciphertext to/from
the remote SMTP client.
.SH "SECURITY"
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The \fBtlsproxy\fR(8) server is moderately security\-sensitive.
It talks to untrusted clients on the network. The process
can be run chrooted at fixed low privilege.
.SH DIAGNOSTICS
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Problems and transactions are logged to \fBsyslogd\fR(8)
or \fBpostlogd\fR(8).
.SH "CONFIGURATION PARAMETERS"
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Changes to \fBmain.cf\fR are not picked up automatically,
as \fBtlsproxy\fR(8) processes may run for a long time
depending on mail server load.  Use the command "\fBpostfix
reload\fR" to speed up a change.

The text below provides only a parameter summary. See
\fBpostconf\fR(5) for more details including examples.
.SH "STARTTLS GLOBAL CONTROLS"
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The following settings are global and therefore cannot be
overruled by information specified in a \fBtlsproxy\fR(8)
client request.
.IP "\fBtls_append_default_CA (no)\fR"
Append the system\-supplied default Certification Authority
certificates to the ones specified with *_tls_CApath or *_tls_CAfile.
.IP "\fBtls_daemon_random_bytes (32)\fR"
The number of pseudo\-random bytes that an \fBsmtp\fR(8) or \fBsmtpd\fR(8)
process requests from the \fBtlsmgr\fR(8) server in order to seed its
internal pseudo random number generator (PRNG).
.IP "\fBtls_high_cipherlist (see 'postconf -d' output)\fR"
The OpenSSL cipherlist for "high" grade ciphers.
.IP "\fBtls_medium_cipherlist (see 'postconf -d' output)\fR"
The OpenSSL cipherlist for "medium" or higher grade ciphers.
.IP "\fBtls_null_cipherlist (eNULL:!aNULL)\fR"
The OpenSSL cipherlist for "NULL" grade ciphers that provide
authentication without encryption.
.IP "\fBtls_eecdh_strong_curve (prime256v1)\fR"
The elliptic curve used by the Postfix SMTP server for sensibly
strong
ephemeral ECDH key exchange.
.IP "\fBtls_eecdh_ultra_curve (secp384r1)\fR"
The elliptic curve used by the Postfix SMTP server for maximally
strong
ephemeral ECDH key exchange.
.IP "\fBtls_disable_workarounds (see 'postconf -d' output)\fR"
List or bit\-mask of OpenSSL bug work\-arounds to disable.
.IP "\fBtls_preempt_cipherlist (no)\fR"
With SSLv3 and later, use the Postfix SMTP server's cipher
preference order instead of the remote client's cipher preference
order.
.PP
Available in Postfix version 2.8..3.7:
.IP "\fBtls_low_cipherlist (see 'postconf -d' output)\fR"
The OpenSSL cipherlist for "low" or higher grade ciphers.
.IP "\fBtls_export_cipherlist (see 'postconf -d' output)\fR"
The OpenSSL cipherlist for "export" or higher grade ciphers.
.PP
Available in Postfix version 2.9 and later:
.IP "\fBtls_legacy_public_key_fingerprints (no)\fR"
A temporary migration aid for sites that use certificate
\fIpublic\-key\fR fingerprints with Postfix 2.9.0..2.9.5, which use
an incorrect algorithm.
.PP
Available in Postfix version 2.11\-3.1:
.IP "\fBtls_dane_digest_agility (on)\fR"
Configure RFC7671 DANE TLSA digest algorithm agility.
.IP "\fBtls_dane_trust_anchor_digest_enable (yes)\fR"
Enable support for RFC 6698 (DANE TLSA) DNS records that contain
digests of trust\-anchors with certificate usage "2".
.PP
Available in Postfix version 2.11 and later:
.IP "\fBtlsmgr_service_name (tlsmgr)\fR"
The name of the \fBtlsmgr\fR(8) service entry in master.cf.
.PP
Available in Postfix version 3.0 and later:
.IP "\fBtls_session_ticket_cipher (Postfix >= 3.0: aes\-256\-cbc, Postfix < 3.0: aes\-128\-cbc)\fR"
Algorithm used to encrypt RFC5077 TLS session tickets.
.IP "\fBopenssl_path (openssl)\fR"
The location of the OpenSSL command line program \fBopenssl\fR(1).
.PP
Available in Postfix version 3.2 and later:
.IP "\fBtls_eecdh_auto_curves (see 'postconf -d' output)\fR"
The prioritized list of elliptic curves supported by the Postfix
SMTP client and server.
.PP
Available in Postfix version 3.4 and later:
.IP "\fBtls_server_sni_maps (empty)\fR"
Optional lookup tables that map names received from remote SMTP
clients via the TLS Server Name Indication (SNI) extension to the
appropriate keys and certificate chains.
.PP
Available in Postfix 3.5, 3.4.6, 3.3.5, 3.2.10, 3.1.13 and later:
.IP "\fBtls_fast_shutdown_enable (yes)\fR"
A workaround for implementations that hang Postfix while shutting
down a TLS session, until Postfix times out.
.PP
Available in Postfix version 3.8 and later:
.IP "\fBtls_ffdhe_auto_groups (see 'postconf -d' output)\fR"
The prioritized list of finite\-field Diffie\-Hellman ephemeral
(FFDHE) key exchange groups supported by the Postfix SMTP client and
server.
.PP
Available in Postfix 3.9, 3.8.1, 3.7.6, 3.6.10, 3.5.20 and later:
.IP "\fBtls_config_file (default)\fR"
Optional configuration file with baseline OpenSSL settings.
.IP "\fBtls_config_name (empty)\fR"
The application name passed by Postfix to OpenSSL library
initialization functions.
.SH "STARTTLS SERVER CONTROLS"
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These settings are clones of Postfix SMTP server settings.
They allow \fBtlsproxy\fR(8) to load the same certificate
and private key information as the Postfix SMTP server,
before dropping privileges, so that the key files can be
kept read\-only for root. These settings can currently not
be overruled by information in a \fBtlsproxy\fR(8) client
request, but that limitation may be removed in a future
version.
.IP "\fBtlsproxy_tls_CAfile ($smtpd_tls_CAfile)\fR"
A file containing (PEM format) CA certificates of root CAs
trusted to sign either remote SMTP client certificates or intermediate
CA certificates.
.IP "\fBtlsproxy_tls_CApath ($smtpd_tls_CApath)\fR"
A directory containing (PEM format) CA certificates of root CAs
trusted to sign either remote SMTP client certificates or intermediate
CA certificates.
.IP "\fBtlsproxy_tls_always_issue_session_ids ($smtpd_tls_always_issue_session_ids)\fR"
Force the Postfix \fBtlsproxy\fR(8) server to issue a TLS session id,
even when TLS session caching is turned off.
.IP "\fBtlsproxy_tls_ask_ccert ($smtpd_tls_ask_ccert)\fR"
Ask a remote SMTP client for a client certificate.
.IP "\fBtlsproxy_tls_ccert_verifydepth ($smtpd_tls_ccert_verifydepth)\fR"
The verification depth for remote SMTP client certificates.
.IP "\fBtlsproxy_tls_cert_file ($smtpd_tls_cert_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) server RSA certificate in PEM
format.
.IP "\fBtlsproxy_tls_ciphers ($smtpd_tls_ciphers)\fR"
The minimum TLS cipher grade that the Postfix \fBtlsproxy\fR(8) server
will use with opportunistic TLS encryption.
.IP "\fBtlsproxy_tls_dcert_file ($smtpd_tls_dcert_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) server DSA certificate in PEM
format.
.IP "\fBtlsproxy_tls_dh1024_param_file ($smtpd_tls_dh1024_param_file)\fR"
File with DH parameters that the Postfix \fBtlsproxy\fR(8) server
should use with non\-export EDH ciphers.
.IP "\fBtlsproxy_tls_dh512_param_file ($smtpd_tls_dh512_param_file)\fR"
File with DH parameters that the Postfix \fBtlsproxy\fR(8) server
should use with export\-grade EDH ciphers.
.IP "\fBtlsproxy_tls_dkey_file ($smtpd_tls_dkey_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) server DSA private key in PEM
format.
.IP "\fBtlsproxy_tls_eccert_file ($smtpd_tls_eccert_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) server ECDSA certificate in PEM
format.
.IP "\fBtlsproxy_tls_eckey_file ($smtpd_tls_eckey_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) server ECDSA private key in PEM
format.
.IP "\fBtlsproxy_tls_eecdh_grade ($smtpd_tls_eecdh_grade)\fR"
The Postfix \fBtlsproxy\fR(8) server security grade for ephemeral
elliptic\-curve Diffie\-Hellman (EECDH) key exchange.
.IP "\fBtlsproxy_tls_exclude_ciphers ($smtpd_tls_exclude_ciphers)\fR"
List of ciphers or cipher types to exclude from the \fBtlsproxy\fR(8)
server cipher list at all TLS security levels.
.IP "\fBtlsproxy_tls_fingerprint_digest ($smtpd_tls_fingerprint_digest)\fR"
The message digest algorithm to construct remote SMTP
client\-certificate
fingerprints.
.IP "\fBtlsproxy_tls_key_file ($smtpd_tls_key_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) server RSA private key in PEM
format.
.IP "\fBtlsproxy_tls_loglevel ($smtpd_tls_loglevel)\fR"
Enable additional Postfix \fBtlsproxy\fR(8) server logging of TLS
activity.
.IP "\fBtlsproxy_tls_mandatory_ciphers ($smtpd_tls_mandatory_ciphers)\fR"
The minimum TLS cipher grade that the Postfix \fBtlsproxy\fR(8) server
will use with mandatory TLS encryption.
.IP "\fBtlsproxy_tls_mandatory_exclude_ciphers ($smtpd_tls_mandatory_exclude_ciphers)\fR"
Additional list of ciphers or cipher types to exclude from the
\fBtlsproxy\fR(8) server cipher list at mandatory TLS security levels.
.IP "\fBtlsproxy_tls_mandatory_protocols ($smtpd_tls_mandatory_protocols)\fR"
The SSL/TLS protocols accepted by the Postfix \fBtlsproxy\fR(8) server
with mandatory TLS encryption.
.IP "\fBtlsproxy_tls_protocols ($smtpd_tls_protocols)\fR"
List of TLS protocols that the Postfix \fBtlsproxy\fR(8) server will
exclude or include with opportunistic TLS encryption.
.IP "\fBtlsproxy_tls_req_ccert ($smtpd_tls_req_ccert)\fR"
With mandatory TLS encryption, require a trusted remote SMTP
client certificate in order to allow TLS connections to proceed.
.IP "\fBtlsproxy_tls_security_level ($smtpd_tls_security_level)\fR"
The SMTP TLS security level for the Postfix \fBtlsproxy\fR(8) server;
when a non\-empty value is specified, this overrides the obsolete
parameters smtpd_use_tls and smtpd_enforce_tls.
.IP "\fBtlsproxy_tls_chain_files ($smtpd_tls_chain_files)\fR"
Files with the Postfix \fBtlsproxy\fR(8) server keys and certificate
chains in PEM format.
.SH "STARTTLS CLIENT CONTROLS"
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These settings are clones of Postfix SMTP client settings.
They allow \fBtlsproxy\fR(8) to load the same certificate
and private key information as the Postfix SMTP client,
before dropping privileges, so that the key files can be
kept read\-only for root. Some settings may be overruled by
information in a \fBtlsproxy\fR(8) client request.
.PP
Available in Postfix version 3.4 and later:
.IP "\fBtlsproxy_client_CAfile ($smtp_tls_CAfile)\fR"
A file containing CA certificates of root CAs trusted to sign
either remote TLS server certificates or intermediate CA certificates.
.IP "\fBtlsproxy_client_CApath ($smtp_tls_CApath)\fR"
Directory with PEM format Certification Authority certificates
that the Postfix \fBtlsproxy\fR(8) client uses to verify a remote TLS
server certificate.
.IP "\fBtlsproxy_client_chain_files ($smtp_tls_chain_files)\fR"
Files with the Postfix \fBtlsproxy\fR(8) client keys and certificate
chains in PEM format.
.IP "\fBtlsproxy_client_cert_file ($smtp_tls_cert_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) client RSA certificate in PEM
format.
.IP "\fBtlsproxy_client_key_file ($smtp_tls_key_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) client RSA private key in PEM
format.
.IP "\fBtlsproxy_client_dcert_file ($smtp_tls_dcert_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) client DSA certificate in PEM
format.
.IP "\fBtlsproxy_client_dkey_file ($smtp_tls_dkey_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) client DSA private key in PEM
format.
.IP "\fBtlsproxy_client_eccert_file ($smtp_tls_eccert_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) client ECDSA certificate in PEM
format.
.IP "\fBtlsproxy_client_eckey_file ($smtp_tls_eckey_file)\fR"
File with the Postfix \fBtlsproxy\fR(8) client ECDSA private key in PEM
format.
.IP "\fBtlsproxy_client_fingerprint_digest ($smtp_tls_fingerprint_digest)\fR"
The message digest algorithm used to construct remote TLS server
certificate fingerprints.
.IP "\fBtlsproxy_client_loglevel ($smtp_tls_loglevel)\fR"
Enable additional Postfix \fBtlsproxy\fR(8) client logging of TLS
activity.
.IP "\fBtlsproxy_client_loglevel_parameter (smtp_tls_loglevel)\fR"
The name of the parameter that provides the tlsproxy_client_loglevel
value.
.IP "\fBtlsproxy_client_scert_verifydepth ($smtp_tls_scert_verifydepth)\fR"
The verification depth for remote TLS server certificates.
.IP "\fBtlsproxy_client_use_tls ($smtp_use_tls)\fR"
Opportunistic mode: use TLS when a remote server announces TLS
support.
.IP "\fBtlsproxy_client_enforce_tls ($smtp_enforce_tls)\fR"
Enforcement mode: require that SMTP servers use TLS encryption.
.IP "\fBtlsproxy_client_per_site ($smtp_tls_per_site)\fR"
Optional lookup tables with the Postfix \fBtlsproxy\fR(8) client TLS
usage policy by next\-hop destination and by remote TLS server
hostname.
.PP
Available in Postfix version 3.4\-3.6:
.IP "\fBtlsproxy_client_level ($smtp_tls_security_level)\fR"
The default TLS security level for the Postfix \fBtlsproxy\fR(8)
client.
.IP "\fBtlsproxy_client_policy ($smtp_tls_policy_maps)\fR"
Optional lookup tables with the Postfix \fBtlsproxy\fR(8) client TLS
security policy by next\-hop destination.
.PP
Available in Postfix version 3.7 and later:
.IP "\fBtlsproxy_client_security_level ($smtp_tls_security_level)\fR"
The default TLS security level for the Postfix \fBtlsproxy\fR(8)
client.
.IP "\fBtlsproxy_client_policy_maps ($smtp_tls_policy_maps)\fR"
Optional lookup tables with the Postfix \fBtlsproxy\fR(8) client TLS
security policy by next\-hop destination.
.SH "OBSOLETE STARTTLS SUPPORT CONTROLS"
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These parameters are supported for compatibility with
\fBsmtpd\fR(8) legacy parameters.
.IP "\fBtlsproxy_use_tls ($smtpd_use_tls)\fR"
Opportunistic TLS: announce STARTTLS support to remote SMTP clients,
but do not require that clients use TLS encryption.
.IP "\fBtlsproxy_enforce_tls ($smtpd_enforce_tls)\fR"
Mandatory TLS: announce STARTTLS support to remote SMTP clients, and
require that clients use TLS encryption.
.IP "\fBtlsproxy_client_use_tls ($smtp_use_tls)\fR"
Opportunistic mode: use TLS when a remote server announces TLS
support.
.IP "\fBtlsproxy_client_enforce_tls ($smtp_enforce_tls)\fR"
Enforcement mode: require that SMTP servers use TLS encryption.
.SH "RESOURCE CONTROLS"
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.IP "\fBtlsproxy_watchdog_timeout (10s)\fR"
How much time a \fBtlsproxy\fR(8) process may take to process local
or remote I/O before it is terminated by a built\-in watchdog timer.
.SH "MISCELLANEOUS CONTROLS"
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.IP "\fBconfig_directory (see 'postconf -d' output)\fR"
The default location of the Postfix main.cf and master.cf
configuration files.
.IP "\fBprocess_id (read\-only)\fR"
The process ID of a Postfix command or daemon process.
.IP "\fBprocess_name (read\-only)\fR"
The process name of a Postfix command or daemon process.
.IP "\fBsyslog_facility (mail)\fR"
The syslog facility of Postfix logging.
.IP "\fBsyslog_name (see 'postconf -d' output)\fR"
A prefix that is prepended to the process name in syslog
records, so that, for example, "smtpd" becomes "prefix/smtpd".
.PP
Available in Postfix 3.3 and later:
.IP "\fBservice_name (read\-only)\fR"
The master.cf service name of a Postfix daemon process.
.SH "SEE ALSO"
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postscreen(8), Postfix zombie blocker
smtpd(8), Postfix SMTP server
postconf(5), configuration parameters
postlogd(8), Postfix logging
syslogd(8), system logging
.SH "LICENSE"
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The Secure Mailer license must be distributed with this software.
.SH HISTORY
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This service was introduced with Postfix version 2.8.
.SH "AUTHOR(S)"
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Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA

Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA