Adding upstream version 4.22.0.upstream/4.22.0

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1349 insertions, 0 deletions

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+.\"	$OpenBSD: ssh-keygen.1,v 1.230 2023/09/04 10:29:58 job Exp $
+.\"
+.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
+.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+.\"                    All rights reserved
+.\"
+.\" As far as I am concerned, the code I have written for this software
+.\" can be used freely for any purpose.  Any derived versions of this
+.\" software must be clearly marked as such, and if the derived work is
+.\" incompatible with the protocol description in the RFC file, it must be
+.\" called by a name other than "ssh" or "Secure Shell".
+.\"
+.\"
+.\" Copyright (c) 1999,2000 Markus Friedl.  All rights reserved.
+.\" Copyright (c) 1999 Aaron Campbell.  All rights reserved.
+.\" Copyright (c) 1999 Theo de Raadt.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"
+.Dd $Mdocdate: September 4 2023 $
+.Dt SSH-KEYGEN 1
+.Os
+.Sh NAME
+.Nm ssh-keygen
+.Nd OpenSSH authentication key utility
+.Sh SYNOPSIS
+.Nm ssh-keygen
+.Op Fl q
+.Op Fl a Ar rounds
+.Op Fl b Ar bits
+.Op Fl C Ar comment
+.Op Fl f Ar output_keyfile
+.Op Fl m Ar format
+.Op Fl N Ar new_passphrase
+.Op Fl O Ar option
+.Op Fl t Cm dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa
+.Op Fl w Ar provider
+.Op Fl Z Ar cipher
+.Nm ssh-keygen
+.Fl p
+.Op Fl a Ar rounds
+.Op Fl f Ar keyfile
+.Op Fl m Ar format
+.Op Fl N Ar new_passphrase
+.Op Fl P Ar old_passphrase
+.Op Fl Z Ar cipher
+.Nm ssh-keygen
+.Fl i
+.Op Fl f Ar input_keyfile
+.Op Fl m Ar key_format
+.Nm ssh-keygen
+.Fl e
+.Op Fl f Ar input_keyfile
+.Op Fl m Ar key_format
+.Nm ssh-keygen
+.Fl y
+.Op Fl f Ar input_keyfile
+.Nm ssh-keygen
+.Fl c
+.Op Fl a Ar rounds
+.Op Fl C Ar comment
+.Op Fl f Ar keyfile
+.Op Fl P Ar passphrase
+.Nm ssh-keygen
+.Fl l
+.Op Fl v
+.Op Fl E Ar fingerprint_hash
+.Op Fl f Ar input_keyfile
+.Nm ssh-keygen
+.Fl B
+.Op Fl f Ar input_keyfile
+.Nm ssh-keygen
+.Fl D Ar pkcs11
+.Nm ssh-keygen
+.Fl F Ar hostname
+.Op Fl lv
+.Op Fl f Ar known_hosts_file
+.Nm ssh-keygen
+.Fl H
+.Op Fl f Ar known_hosts_file
+.Nm ssh-keygen
+.Fl K
+.Op Fl a Ar rounds
+.Op Fl w Ar provider
+.Nm ssh-keygen
+.Fl R Ar hostname
+.Op Fl f Ar known_hosts_file
+.Nm ssh-keygen
+.Fl r Ar hostname
+.Op Fl g
+.Op Fl f Ar input_keyfile
+.Nm ssh-keygen
+.Fl M Cm generate
+.Op Fl O Ar option
+.Ar output_file
+.Nm ssh-keygen
+.Fl M Cm screen
+.Op Fl f Ar input_file
+.Op Fl O Ar option
+.Ar output_file
+.Nm ssh-keygen
+.Fl I Ar certificate_identity
+.Fl s Ar ca_key
+.Op Fl hU
+.Op Fl D Ar pkcs11_provider
+.Op Fl n Ar principals
+.Op Fl O Ar option
+.Op Fl V Ar validity_interval
+.Op Fl z Ar serial_number
+.Ar
+.Nm ssh-keygen
+.Fl L
+.Op Fl f Ar input_keyfile
+.Nm ssh-keygen
+.Fl A
+.Op Fl a Ar rounds
+.Op Fl f Ar prefix_path
+.Nm ssh-keygen
+.Fl k
+.Fl f Ar krl_file
+.Op Fl u
+.Op Fl s Ar ca_public
+.Op Fl z Ar version_number
+.Ar
+.Nm ssh-keygen
+.Fl Q
+.Op Fl l
+.Fl f Ar krl_file
+.Ar
+.Nm ssh-keygen
+.Fl Y Cm find-principals
+.Op Fl O Ar option
+.Fl s Ar signature_file
+.Fl f Ar allowed_signers_file
+.Nm ssh-keygen
+.Fl Y Cm match-principals
+.Fl I Ar signer_identity
+.Fl f Ar allowed_signers_file
+.Nm ssh-keygen
+.Fl Y Cm check-novalidate
+.Op Fl O Ar option
+.Fl n Ar namespace
+.Fl s Ar signature_file
+.Nm ssh-keygen
+.Fl Y Cm sign
+.Op Fl O Ar option
+.Fl f Ar key_file
+.Fl n Ar namespace
+.Ar
+.Nm ssh-keygen
+.Fl Y Cm verify
+.Op Fl O Ar option
+.Fl f Ar allowed_signers_file
+.Fl I Ar signer_identity
+.Fl n Ar namespace
+.Fl s Ar signature_file
+.Op Fl r Ar revocation_file
+.Sh DESCRIPTION
+.Nm
+generates, manages and converts authentication keys for
+.Xr ssh 1 .
+.Nm
+can create keys for use by SSH protocol version 2.
+.Pp
+The type of key to be generated is specified with the
+.Fl t
+option.
+If invoked without any arguments,
+.Nm
+will generate an Ed25519 key.
+.Pp
+.Nm
+is also used to generate groups for use in Diffie-Hellman group
+exchange (DH-GEX).
+See the
+.Sx MODULI GENERATION
+section for details.
+.Pp
+Finally,
+.Nm
+can be used to generate and update Key Revocation Lists, and to test whether
+given keys have been revoked by one.
+See the
+.Sx KEY REVOCATION LISTS
+section for details.
+.Pp
+Normally each user wishing to use SSH
+with public key authentication runs this once to create the authentication
+key in
+.Pa ~/.ssh/id_dsa ,
+.Pa ~/.ssh/id_ecdsa ,
+.Pa ~/.ssh/id_ecdsa_sk ,
+.Pa ~/.ssh/id_ed25519 ,
+.Pa ~/.ssh/id_ed25519_sk
+or
+.Pa ~/.ssh/id_rsa .
+Additionally, the system administrator may use this to generate host keys,
+as seen in
+.Pa /etc/rc .
+.Pp
+Normally this program generates the key and asks for a file in which
+to store the private key.
+The public key is stored in a file with the same name but
+.Dq .pub
+appended.
+The program also asks for a passphrase.
+The passphrase may be empty to indicate no passphrase
+(host keys must have an empty passphrase), or it may be a string of
+arbitrary length.
+A passphrase is similar to a password, except it can be a phrase with a
+series of words, punctuation, numbers, whitespace, or any string of
+characters you want.
+Good passphrases are 10-30 characters long, are
+not simple sentences or otherwise easily guessable (English
+prose has only 1-2 bits of entropy per character, and provides very bad
+passphrases), and contain a mix of upper and lowercase letters,
+numbers, and non-alphanumeric characters.
+The passphrase can be changed later by using the
+.Fl p
+option.
+.Pp
+There is no way to recover a lost passphrase.
+If the passphrase is lost or forgotten, a new key must be generated
+and the corresponding public key copied to other machines.
+.Pp
+.Nm
+will by default write keys in an OpenSSH-specific format.
+This format is preferred as it offers better protection for
+keys at rest as well as allowing storage of key comments within
+the private key file itself.
+The key comment may be useful to help identify the key.
+The comment is initialized to
+.Dq user@host
+when the key is created, but can be changed using the
+.Fl c
+option.
+.Pp
+It is still possible for
+.Nm
+to write the previously-used PEM format private keys using the
+.Fl m
+flag.
+This may be used when generating new keys, and existing new-format
+keys may be converted using this option in conjunction with the
+.Fl p
+(change passphrase) flag.
+.Pp
+After a key is generated,
+.Nm
+will ask where the keys
+should be placed to be activated.
+.Pp
+The options are as follows:
+.Bl -tag -width Ds
+.It Fl A
+Generate host keys of all default key types (rsa, ecdsa, and
+ed25519) if they do not already exist.
+The host keys are generated with the default key file path,
+an empty passphrase, default bits for the key type, and default comment.
+If
+.Fl f
+has also been specified, its argument is used as a prefix to the
+default path for the resulting host key files.
+This is used by
+.Pa /etc/rc
+to generate new host keys.
+.It Fl a Ar rounds
+When saving a private key, this option specifies the number of KDF
+(key derivation function, currently
+.Xr bcrypt_pbkdf 3 )
+rounds used.
+Higher numbers result in slower passphrase verification and increased
+resistance to brute-force password cracking (should the keys be stolen).
+The default is 16 rounds.
+.It Fl B
+Show the bubblebabble digest of specified private or public key file.
+.It Fl b Ar bits
+Specifies the number of bits in the key to create.
+For RSA keys, the minimum size is 1024 bits and the default is 3072 bits.
+Generally, 3072 bits is considered sufficient.
+DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
+For ECDSA keys, the
+.Fl b
+flag determines the key length by selecting from one of three elliptic
+curve sizes: 256, 384 or 521 bits.
+Attempting to use bit lengths other than these three values for ECDSA keys
+will fail.
+ECDSA-SK, Ed25519 and Ed25519-SK keys have a fixed length and the
+.Fl b
+flag will be ignored.
+.It Fl C Ar comment
+Provides a new comment.
+.It Fl c
+Requests changing the comment in the private and public key files.
+The program will prompt for the file containing the private keys, for
+the passphrase if the key has one, and for the new comment.
+.It Fl D Ar pkcs11
+Download the public keys provided by the PKCS#11 shared library
+.Ar pkcs11 .
+When used in combination with
+.Fl s ,
+this option indicates that a CA key resides in a PKCS#11 token (see the
+.Sx CERTIFICATES
+section for details).
+.It Fl E Ar fingerprint_hash
+Specifies the hash algorithm used when displaying key fingerprints.
+Valid options are:
+.Dq md5
+and
+.Dq sha256 .
+The default is
+.Dq sha256 .
+.It Fl e
+This option will read a private or public OpenSSH key file and
+print to stdout a public key in one of the formats specified by the
+.Fl m
+option.
+The default export format is
+.Dq RFC4716 .
+This option allows exporting OpenSSH keys for use by other programs, including
+several commercial SSH implementations.
+.It Fl F Ar hostname | [hostname]:port
+Search for the specified
+.Ar hostname
+(with optional port number)
+in a
+.Pa known_hosts
+file, listing any occurrences found.
+This option is useful to find hashed host names or addresses and may also be
+used in conjunction with the
+.Fl H
+option to print found keys in a hashed format.
+.It Fl f Ar filename
+Specifies the filename of the key file.
+.It Fl g
+Use generic DNS format when printing fingerprint resource records using the
+.Fl r
+command.
+.It Fl H
+Hash a
+.Pa known_hosts
+file.
+This replaces all hostnames and addresses with hashed representations
+within the specified file; the original content is moved to a file with
+a .old suffix.
+These hashes may be used normally by
+.Nm ssh
+and
+.Nm sshd ,
+but they do not reveal identifying information should the file's contents
+be disclosed.
+This option will not modify existing hashed hostnames and is therefore safe
+to use on files that mix hashed and non-hashed names.
+.It Fl h
+When signing a key, create a host certificate instead of a user
+certificate.
+See the
+.Sx CERTIFICATES
+section for details.
+.It Fl I Ar certificate_identity
+Specify the key identity when signing a public key.
+See the
+.Sx CERTIFICATES
+section for details.
+.It Fl i
+This option will read an unencrypted private (or public) key file
+in the format specified by the
+.Fl m
+option and print an OpenSSH compatible private
+(or public) key to stdout.
+This option allows importing keys from other software, including several
+commercial SSH implementations.
+The default import format is
+.Dq RFC4716 .
+.It Fl K
+Download resident keys from a FIDO authenticator.
+Public and private key files will be written to the current directory for
+each downloaded key.
+If multiple FIDO authenticators are attached, keys will be downloaded from
+the first touched authenticator.
+See the
+.Sx FIDO AUTHENTICATOR
+section for more information.
+.It Fl k
+Generate a KRL file.
+In this mode,
+.Nm
+will generate a KRL file at the location specified via the
+.Fl f
+flag that revokes every key or certificate presented on the command line.
+Keys/certificates to be revoked may be specified by public key file or
+using the format described in the
+.Sx KEY REVOCATION LISTS
+section.
+.It Fl L
+Prints the contents of one or more certificates.
+.It Fl l
+Show fingerprint of specified public key file.
+For RSA and DSA keys
+.Nm
+tries to find the matching public key file and prints its fingerprint.
+If combined with
+.Fl v ,
+a visual ASCII art representation of the key is supplied with the
+fingerprint.
+.It Fl M Cm generate
+Generate candidate Diffie-Hellman Group Exchange (DH-GEX) parameters for
+eventual use by the
+.Sq diffie-hellman-group-exchange-*
+key exchange methods.
+The numbers generated by this operation must be further screened before
+use.
+See the
+.Sx MODULI GENERATION
+section for more information.
+.It Fl M Cm screen
+Screen candidate parameters for Diffie-Hellman Group Exchange.
+This will accept a list of candidate numbers and test that they are
+safe (Sophie Germain) primes with acceptable group generators.
+The results of this operation may be added to the
+.Pa /etc/ssh/moduli
+file.
+See the
+.Sx MODULI GENERATION
+section for more information.
+.It Fl m Ar key_format
+Specify a key format for key generation, the
+.Fl i
+(import),
+.Fl e
+(export) conversion options, and the
+.Fl p
+change passphrase operation.
+The latter may be used to convert between OpenSSH private key and PEM
+private key formats.
+The supported key formats are:
+.Dq RFC4716
+(RFC 4716/SSH2 public or private key),
+.Dq PKCS8
+(PKCS8 public or private key)
+or
+.Dq PEM
+(PEM public key).
+By default OpenSSH will write newly-generated private keys in its own
+format, but when converting public keys for export the default format is
+.Dq RFC4716 .
+Setting a format of
+.Dq PEM
+when generating or updating a supported private key type will cause the
+key to be stored in the legacy PEM private key format.
+.It Fl N Ar new_passphrase
+Provides the new passphrase.
+.It Fl n Ar principals
+Specify one or more principals (user or host names) to be included in
+a certificate when signing a key.
+Multiple principals may be specified, separated by commas.
+See the
+.Sx CERTIFICATES
+section for details.
+.It Fl O Ar option
+Specify a key/value option.
+These are specific to the operation that
+.Nm
+has been requested to perform.
+.Pp
+When signing certificates, one of the options listed in the
+.Sx CERTIFICATES
+section may be specified here.
+.Pp
+When performing moduli generation or screening, one of the options
+listed in the
+.Sx MODULI GENERATION
+section may be specified.
+.Pp
+When generating FIDO authenticator-backed keys, the options listed in the
+.Sx FIDO AUTHENTICATOR
+section may be specified.
+.Pp
+When performing signature-related options using the
+.Fl Y
+flag, the following options are accepted:
+.Bl -tag -width Ds
+.It Cm hashalg Ns = Ns Ar algorithm
+Selects the hash algorithm to use for hashing the message to be signed.
+Valid algorithms are
+.Dq sha256
+and
+.Dq sha512.
+The default is
+.Dq sha512.
+.It Cm print-pubkey
+Print the full public key to standard output after signature verification.
+.It Cm verify-time Ns = Ns Ar timestamp
+Specifies a time to use when validating signatures instead of the current
+time.
+The time may be specified as a date or time in the YYYYMMDD[Z] or
+in YYYYMMDDHHMM[SS][Z] formats.
+Dates and times will be interpreted in the current system time zone unless
+suffixed with a Z character, which causes them to be interpreted in the
+UTC time zone.
+.El
+.Pp
+When generating SSHFP DNS records from public keys using the
+.Fl r
+flag, the following options are accepted:
+.Bl -tag -width Ds
+.It Cm hashalg Ns = Ns Ar algorithm
+Selects a hash algorithm to use when printing SSHFP records using the
+.Fl D
+flag.
+Valid algorithms are
+.Dq sha1
+and
+.Dq sha256 .
+The default is to print both.
+.El
+.Pp
+The
+.Fl O
+option may be specified multiple times.
+.It Fl P Ar passphrase
+Provides the (old) passphrase.
+.It Fl p
+Requests changing the passphrase of a private key file instead of
+creating a new private key.
+The program will prompt for the file
+containing the private key, for the old passphrase, and twice for the
+new passphrase.
+.It Fl Q
+Test whether keys have been revoked in a KRL.
+If the
+.Fl l
+option is also specified then the contents of the KRL will be printed.
+.It Fl q
+Silence
+.Nm ssh-keygen .
+.It Fl R Ar hostname | [hostname]:port
+Removes all keys belonging to the specified
+.Ar hostname
+(with optional port number)
+from a
+.Pa known_hosts
+file.
+This option is useful to delete hashed hosts (see the
+.Fl H
+option above).
+.It Fl r Ar hostname
+Print the SSHFP fingerprint resource record named
+.Ar hostname
+for the specified public key file.
+.It Fl s Ar ca_key
+Certify (sign) a public key using the specified CA key.
+See the
+.Sx CERTIFICATES
+section for details.
+.Pp
+When generating a KRL,
+.Fl s
+specifies a path to a CA public key file used to revoke certificates directly
+by key ID or serial number.
+See the
+.Sx KEY REVOCATION LISTS
+section for details.
+.It Fl t Cm dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa
+Specifies the type of key to create.
+The possible values are
+.Dq dsa ,
+.Dq ecdsa ,
+.Dq ecdsa-sk ,
+.Dq ed25519 ,
+.Dq ed25519-sk ,
+or
+.Dq rsa .
+.Pp
+This flag may also be used to specify the desired signature type when
+signing certificates using an RSA CA key.
+The available RSA signature variants are
+.Dq ssh-rsa
+(SHA1 signatures, not recommended),
+.Dq rsa-sha2-256 ,
+and
+.Dq rsa-sha2-512
+(the default).
+.It Fl U
+When used in combination with
+.Fl s
+or
+.Fl Y Cm sign ,
+this option indicates that a CA key resides in a
+.Xr ssh-agent 1 .
+See the
+.Sx CERTIFICATES
+section for more information.
+.It Fl u
+Update a KRL.
+When specified with
+.Fl k ,
+keys listed via the command line are added to the existing KRL rather than
+a new KRL being created.
+.It Fl V Ar validity_interval
+Specify a validity interval when signing a certificate.
+A validity interval may consist of a single time, indicating that the
+certificate is valid beginning now and expiring at that time, or may consist
+of two times separated by a colon to indicate an explicit time interval.
+.Pp
+The start time may be specified as:
+.Bl -bullet -compact
+.It
+The string
+.Dq always
+to indicate the certificate has no specified start time.
+.It
+A date or time in the system time zone formatted as YYYYMMDD or
+YYYYMMDDHHMM[SS].
+.It
+A date or time in the UTC time zone as YYYYMMDDZ or YYYYMMDDHHMM[SS]Z.
+.It
+A relative time before the current system time consisting of a minus sign
+followed by an interval in the format described in the
+TIME FORMATS section of
+.Xr sshd_config 5 .
+.It
+A raw seconds since epoch (Jan 1 1970 00:00:00 UTC) as a hexadecimal
+number beginning with
+.Dq 0x .
+.El
+.Pp
+The end time may be specified similarly to the start time:
+.Bl -bullet -compact
+.It
+The string
+.Dq forever
+to indicate the certificate has no specified end time.
+.It
+A date or time in the system time zone formatted as YYYYMMDD or
+YYYYMMDDHHMM[SS].
+.It
+A date or time in the UTC time zone as YYYYMMDDZ or YYYYMMDDHHMM[SS]Z.
+.It
+A relative time after the current system time consisting of a plus sign
+followed by an interval in the format described in the
+TIME FORMATS section of
+.Xr sshd_config 5 .
+.It
+A raw seconds since epoch (Jan 1 1970 00:00:00 UTC) as a hexadecimal
+number beginning with
+.Dq 0x .
+.El
+.Pp
+For example:
+.Bl -tag -width Ds
+.It +52w1d
+Valid from now to 52 weeks and one day from now.
+.It -4w:+4w
+Valid from four weeks ago to four weeks from now.
+.It 20100101123000:20110101123000
+Valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011.
+.It 20100101123000Z:20110101123000Z
+Similar, but interpreted in the UTC time zone rather than the system time zone.
+.It -1d:20110101
+Valid from yesterday to midnight, January 1st, 2011.
+.It 0x1:0x2000000000
+Valid from roughly early 1970 to May 2033.
+.It -1m:forever
+Valid from one minute ago and never expiring.
+.El
+.It Fl v
+Verbose mode.
+Causes
+.Nm
+to print debugging messages about its progress.
+This is helpful for debugging moduli generation.
+Multiple
+.Fl v
+options increase the verbosity.
+The maximum is 3.
+.It Fl w Ar provider
+Specifies a path to a library that will be used when creating
+FIDO authenticator-hosted keys, overriding the default of using
+the internal USB HID support.
+.It Fl Y Cm find-principals
+Find the principal(s) associated with the public key of a signature,
+provided using the
+.Fl s
+flag in an authorized signers file provided using the
+.Fl f
+flag.
+The format of the allowed signers file is documented in the
+.Sx ALLOWED SIGNERS
+section below.
+If one or more matching principals are found, they are returned on
+standard output.
+.It Fl Y Cm match-principals
+Find principal matching the principal name provided using the
+.Fl I
+flag in the authorized signers file specified using the
+.Fl f
+flag.
+If one or more matching principals are found, they are returned on
+standard output.
+.It Fl Y Cm check-novalidate
+Checks that a signature generated using
+.Nm
+.Fl Y Cm sign
+has a valid structure.
+This does not validate if a signature comes from an authorized signer.
+When testing a signature,
+.Nm
+accepts a message on standard input and a signature namespace using
+.Fl n .
+A file containing the corresponding signature must also be supplied using the
+.Fl s
+flag.
+Successful testing of the signature is signalled by
+.Nm
+returning a zero exit status.
+.It Fl Y Cm sign
+Cryptographically sign a file or some data using an SSH key.
+When signing,
+.Nm
+accepts zero or more files to sign on the command-line - if no files
+are specified then
+.Nm
+will sign data presented on standard input.
+Signatures are written to the path of the input file with
+.Dq .sig
+appended, or to standard output if the message to be signed was read from
+standard input.
+.Pp
+The key used for signing is specified using the
+.Fl f
+option and may refer to either a private key, or a public key with the private
+half available via
+.Xr ssh-agent 1 .
+An additional signature namespace, used to prevent signature confusion across
+different domains of use (e.g. file signing vs email signing) must be provided
+via the
+.Fl n
+flag.
+Namespaces are arbitrary strings, and may include:
+.Dq file
+for file signing,
+.Dq email
+for email signing.
+For custom uses, it is recommended to use names following a
+NAMESPACE@YOUR.DOMAIN pattern to generate unambiguous namespaces.
+.It Fl Y Cm verify
+Request to verify a signature generated using
+.Nm
+.Fl Y Cm sign
+as described above.
+When verifying a signature,
+.Nm
+accepts a message on standard input and a signature namespace using
+.Fl n .
+A file containing the corresponding signature must also be supplied using the
+.Fl s
+flag, along with the identity of the signer using
+.Fl I
+and a list of allowed signers via the
+.Fl f
+flag.
+The format of the allowed signers file is documented in the
+.Sx ALLOWED SIGNERS
+section below.
+A file containing revoked keys can be passed using the
+.Fl r
+flag.
+The revocation file may be a KRL or a one-per-line list of public keys.
+Successful verification by an authorized signer is signalled by
+.Nm
+returning a zero exit status.
+.It Fl y
+This option will read a private
+OpenSSH format file and print an OpenSSH public key to stdout.
+.It Fl Z Ar cipher
+Specifies the cipher to use for encryption when writing an OpenSSH-format
+private key file.
+The list of available ciphers may be obtained using
+.Qq ssh -Q cipher .
+The default is
+.Dq aes256-ctr .
+.It Fl z Ar serial_number
+Specifies a serial number to be embedded in the certificate to distinguish
+this certificate from others from the same CA.
+If the
+.Ar serial_number
+is prefixed with a
+.Sq +
+character, then the serial number will be incremented for each certificate
+signed on a single command-line.
+The default serial number is zero.
+.Pp
+When generating a KRL, the
+.Fl z
+flag is used to specify a KRL version number.
+.El
+.Sh MODULI GENERATION
+.Nm
+may be used to generate groups for the Diffie-Hellman Group Exchange
+(DH-GEX) protocol.
+Generating these groups is a two-step process: first, candidate
+primes are generated using a fast, but memory intensive process.
+These candidate primes are then tested for suitability (a CPU-intensive
+process).
+.Pp
+Generation of primes is performed using the
+.Fl M Cm generate
+option.
+The desired length of the primes may be specified by the
+.Fl O Cm bits
+option.
+For example:
+.Pp
+.Dl # ssh-keygen -M generate -O bits=2048 moduli-2048.candidates
+.Pp
+By default, the search for primes begins at a random point in the
+desired length range.
+This may be overridden using the
+.Fl O Cm start
+option, which specifies a different start point (in hex).
+.Pp
+Once a set of candidates have been generated, they must be screened for
+suitability.
+This may be performed using the
+.Fl M Cm screen
+option.
+In this mode
+.Nm
+will read candidates from standard input (or a file specified using the
+.Fl f
+option).
+For example:
+.Pp
+.Dl # ssh-keygen -M screen -f moduli-2048.candidates moduli-2048
+.Pp
+By default, each candidate will be subjected to 100 primality tests.
+This may be overridden using the
+.Fl O Cm prime-tests
+option.
+The DH generator value will be chosen automatically for the
+prime under consideration.
+If a specific generator is desired, it may be requested using the
+.Fl O Cm generator
+option.
+Valid generator values are 2, 3, and 5.
+.Pp
+Screened DH groups may be installed in
+.Pa /etc/ssh/moduli .
+It is important that this file contains moduli of a range of bit lengths.
+.Pp
+A number of options are available for moduli generation and screening via the
+.Fl O
+flag:
+.Bl -tag -width Ds
+.It Ic lines Ns = Ns Ar number
+Exit after screening the specified number of lines while performing DH
+candidate screening.
+.It Ic start-line Ns = Ns Ar line-number
+Start screening at the specified line number while performing DH candidate
+screening.
+.It Ic checkpoint Ns = Ns Ar filename
+Write the last line processed to the specified file while performing DH
+candidate screening.
+This will be used to skip lines in the input file that have already been
+processed if the job is restarted.
+.It Ic memory Ns = Ns Ar mbytes
+Specify the amount of memory to use (in megabytes) when generating
+candidate moduli for DH-GEX.
+.It Ic start Ns = Ns Ar hex-value
+Specify start point (in hex) when generating candidate moduli for DH-GEX.
+.It Ic generator Ns = Ns Ar value
+Specify desired generator (in decimal) when testing candidate moduli for DH-GEX.
+.El
+.Sh CERTIFICATES
+.Nm
+supports signing of keys to produce certificates that may be used for
+user or host authentication.
+Certificates consist of a public key, some identity information, zero or
+more principal (user or host) names and a set of options that
+are signed by a Certification Authority (CA) key.
+Clients or servers may then trust only the CA key and verify its signature
+on a certificate rather than trusting many user/host keys.
+Note that OpenSSH certificates are a different, and much simpler, format to
+the X.509 certificates used in
+.Xr ssl 8 .
+.Pp
+.Nm
+supports two types of certificates: user and host.
+User certificates authenticate users to servers, whereas host certificates
+authenticate server hosts to users.
+To generate a user certificate:
+.Pp
+.Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
+.Pp
+The resultant certificate will be placed in
+.Pa /path/to/user_key-cert.pub .
+A host certificate requires the
+.Fl h
+option:
+.Pp
+.Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
+.Pp
+The host certificate will be output to
+.Pa /path/to/host_key-cert.pub .
+.Pp
+It is possible to sign using a CA key stored in a PKCS#11 token by
+providing the token library using
+.Fl D
+and identifying the CA key by providing its public half as an argument
+to
+.Fl s :
+.Pp
+.Dl $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub
+.Pp
+Similarly, it is possible for the CA key to be hosted in a
+.Xr ssh-agent 1 .
+This is indicated by the
+.Fl U
+flag and, again, the CA key must be identified by its public half.
+.Pp
+.Dl $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub
+.Pp
+In all cases,
+.Ar key_id
+is a "key identifier" that is logged by the server when the certificate
+is used for authentication.
+.Pp
+Certificates may be limited to be valid for a set of principal (user/host)
+names.
+By default, generated certificates are valid for all users or hosts.
+To generate a certificate for a specified set of principals:
+.Pp
+.Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
+.Dl "$ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub"
+.Pp
+Additional limitations on the validity and use of user certificates may
+be specified through certificate options.
+A certificate option may disable features of the SSH session, may be
+valid only when presented from particular source addresses or may
+force the use of a specific command.
+.Pp
+The options that are valid for user certificates are:
+.Pp
+.Bl -tag -width Ds -compact
+.It Ic clear
+Clear all enabled permissions.
+This is useful for clearing the default set of permissions so permissions may
+be added individually.
+.Pp
+.It Ic critical : Ns Ar name Ns Op Ns = Ns Ar contents
+.It Ic extension : Ns Ar name Ns Op Ns = Ns Ar contents
+Includes an arbitrary certificate critical option or extension.
+The specified
+.Ar name
+should include a domain suffix, e.g.\&
+.Dq name@example.com .
+If
+.Ar contents
+is specified then it is included as the contents of the extension/option
+encoded as a string, otherwise the extension/option is created with no
+contents (usually indicating a flag).
+Extensions may be ignored by a client or server that does not recognise them,
+whereas unknown critical options will cause the certificate to be refused.
+.Pp
+.It Ic force-command Ns = Ns Ar command
+Forces the execution of
+.Ar command
+instead of any shell or command specified by the user when
+the certificate is used for authentication.
+.Pp
+.It Ic no-agent-forwarding
+Disable
+.Xr ssh-agent 1
+forwarding (permitted by default).
+.Pp
+.It Ic no-port-forwarding
+Disable port forwarding (permitted by default).
+.Pp
+.It Ic no-pty
+Disable PTY allocation (permitted by default).
+.Pp
+.It Ic no-user-rc
+Disable execution of
+.Pa ~/.ssh/rc
+by
+.Xr sshd 8
+(permitted by default).
+.Pp
+.It Ic no-x11-forwarding
+Disable X11 forwarding (permitted by default).
+.Pp
+.It Ic permit-agent-forwarding
+Allows
+.Xr ssh-agent 1
+forwarding.
+.Pp
+.It Ic permit-port-forwarding
+Allows port forwarding.
+.Pp
+.It Ic permit-pty
+Allows PTY allocation.
+.Pp
+.It Ic permit-user-rc
+Allows execution of
+.Pa ~/.ssh/rc
+by
+.Xr sshd 8 .
+.Pp
+.It Ic permit-X11-forwarding
+Allows X11 forwarding.
+.Pp
+.It Ic no-touch-required
+Do not require signatures made using this key include demonstration
+of user presence (e.g. by having the user touch the authenticator).
+This option only makes sense for the FIDO authenticator algorithms
+.Cm ecdsa-sk
+and
+.Cm ed25519-sk .
+.Pp
+.It Ic source-address Ns = Ns Ar address_list
+Restrict the source addresses from which the certificate is considered valid.
+The
+.Ar address_list
+is a comma-separated list of one or more address/netmask pairs in CIDR
+format.
+.Pp
+.It Ic verify-required
+Require signatures made using this key indicate that the user was first
+verified.
+This option only makes sense for the FIDO authenticator algorithms
+.Cm ecdsa-sk
+and
+.Cm ed25519-sk .
+Currently PIN authentication is the only supported verification method,
+but other methods may be supported in the future.
+.El
+.Pp
+At present, no standard options are valid for host keys.
+.Pp
+Finally, certificates may be defined with a validity lifetime.
+The
+.Fl V
+option allows specification of certificate start and end times.
+A certificate that is presented at a time outside this range will not be
+considered valid.
+By default, certificates are valid from the
+.Ux
+Epoch to the distant future.
+.Pp
+For certificates to be used for user or host authentication, the CA
+public key must be trusted by
+.Xr sshd 8
+or
+.Xr ssh 1 .
+Refer to those manual pages for details.
+.Sh FIDO AUTHENTICATOR
+.Nm
+is able to generate FIDO authenticator-backed keys, after which
+they may be used much like any other key type supported by OpenSSH, so
+long as the hardware authenticator is attached when the keys are used.
+FIDO authenticators generally require the user to explicitly authorise
+operations by touching or tapping them.
+FIDO keys consist of two parts: a key handle part stored in the
+private key file on disk, and a per-device private key that is unique
+to each FIDO authenticator and that cannot be exported from the
+authenticator hardware.
+These are combined by the hardware at authentication time to derive
+the real key that is used to sign authentication challenges.
+Supported key types are
+.Cm ecdsa-sk
+and
+.Cm ed25519-sk .
+.Pp
+The options that are valid for FIDO keys are:
+.Bl -tag -width Ds
+.It Cm application
+Override the default FIDO application/origin string of
+.Dq ssh: .
+This may be useful when generating host or domain-specific resident keys.
+The specified application string must begin with
+.Dq ssh: .
+.It Cm challenge Ns = Ns Ar path
+Specifies a path to a challenge string that will be passed to the
+FIDO authenticator during key generation.
+The challenge string may be used as part of an out-of-band
+protocol for key enrollment
+(a random challenge is used by default).
+.It Cm device
+Explicitly specify a
+.Xr fido 4
+device to use, rather than letting the authenticator middleware select one.
+.It Cm no-touch-required
+Indicate that the generated private key should not require touch
+events (user presence) when making signatures.
+Note that
+.Xr sshd 8
+will refuse such signatures by default, unless overridden via
+an authorized_keys option.
+.It Cm resident
+Indicate that the key handle should be stored on the FIDO
+authenticator itself.
+This makes it easier to use the authenticator on multiple computers.
+Resident keys may be supported on FIDO2 authenticators and typically
+require that a PIN be set on the authenticator prior to generation.
+Resident keys may be loaded off the authenticator using
+.Xr ssh-add 1 .
+Storing both parts of a key on a FIDO authenticator increases the likelihood
+of an attacker being able to use a stolen authenticator device.
+.It Cm user
+A username to be associated with a resident key,
+overriding the empty default username.
+Specifying a username may be useful when generating multiple resident keys
+for the same application name.
+.It Cm verify-required
+Indicate that this private key should require user verification for
+each signature.
+Not all FIDO authenticators support this option.
+Currently PIN authentication is the only supported verification method,
+but other methods may be supported in the future.
+.It Cm write-attestation Ns = Ns Ar path
+May be used at key generation time to record the attestation data
+returned from FIDO authenticators during key generation.
+This information is potentially sensitive.
+By default, this information is discarded.
+.El
+.Sh KEY REVOCATION LISTS
+.Nm
+is able to manage OpenSSH format Key Revocation Lists (KRLs).
+These binary files specify keys or certificates to be revoked using a
+compact format, taking as little as one bit per certificate if they are being
+revoked by serial number.
+.Pp
+KRLs may be generated using the
+.Fl k
+flag.
+This option reads one or more files from the command line and generates a new
+KRL.
+The files may either contain a KRL specification (see below) or public keys,
+listed one per line.
+Plain public keys are revoked by listing their hash or contents in the KRL and
+certificates revoked by serial number or key ID (if the serial is zero or
+not available).
+.Pp
+Revoking keys using a KRL specification offers explicit control over the
+types of record used to revoke keys and may be used to directly revoke
+certificates by serial number or key ID without having the complete original
+certificate on hand.
+A KRL specification consists of lines containing one of the following directives
+followed by a colon and some directive-specific information.
+.Bl -tag -width Ds
+.It Cm serial : Ar serial_number Ns Op - Ns Ar serial_number
+Revokes a certificate with the specified serial number.
+Serial numbers are 64-bit values, not including zero and may be expressed
+in decimal, hex or octal.
+If two serial numbers are specified separated by a hyphen, then the range
+of serial numbers including and between each is revoked.
+The CA key must have been specified on the
+.Nm
+command line using the
+.Fl s
+option.
+.It Cm id : Ar key_id
+Revokes a certificate with the specified key ID string.
+The CA key must have been specified on the
+.Nm
+command line using the
+.Fl s
+option.
+.It Cm key : Ar public_key
+Revokes the specified key.
+If a certificate is listed, then it is revoked as a plain public key.
+.It Cm sha1 : Ar public_key
+Revokes the specified key by including its SHA1 hash in the KRL.
+.It Cm sha256 : Ar public_key
+Revokes the specified key by including its SHA256 hash in the KRL.
+KRLs that revoke keys by SHA256 hash are not supported by OpenSSH versions
+prior to 7.9.
+.It Cm hash : Ar fingerprint
+Revokes a key using a fingerprint hash, as obtained from a
+.Xr sshd 8
+authentication log message or the
+.Nm
+.Fl l
+flag.
+Only SHA256 fingerprints are supported here and resultant KRLs are
+not supported by OpenSSH versions prior to 7.9.
+.El
+.Pp
+KRLs may be updated using the
+.Fl u
+flag in addition to
+.Fl k .
+When this option is specified, keys listed via the command line are merged into
+the KRL, adding to those already there.
+.Pp
+It is also possible, given a KRL, to test whether it revokes a particular key
+(or keys).
+The
+.Fl Q
+flag will query an existing KRL, testing each key specified on the command line.
+If any key listed on the command line has been revoked (or an error encountered)
+then
+.Nm
+will exit with a non-zero exit status.
+A zero exit status will only be returned if no key was revoked.
+.Sh ALLOWED SIGNERS
+When verifying signatures,
+.Nm
+uses a simple list of identities and keys to determine whether a signature
+comes from an authorized source.
+This "allowed signers" file uses a format patterned after the
+AUTHORIZED_KEYS FILE FORMAT described in
+.Xr sshd 8 .
+Each line of the file contains the following space-separated fields:
+principals, options, keytype, base64-encoded key.
+Empty lines and lines starting with a
+.Ql #
+are ignored as comments.
+.Pp
+The principals field is a pattern-list (see PATTERNS in
+.Xr ssh_config 5 )
+consisting of one or more comma-separated USER@DOMAIN identity patterns
+that are accepted for signing.
+When verifying, the identity presented via the
+.Fl I
+option must match a principals pattern in order for the corresponding key to be
+considered acceptable for verification.
+.Pp
+The options (if present) consist of comma-separated option specifications.
+No spaces are permitted, except within double quotes.
+The following option specifications are supported (note that option keywords
+are case-insensitive):
+.Bl -tag -width Ds
+.It Cm cert-authority
+Indicates that this key is accepted as a certificate authority (CA) and
+that certificates signed by this CA may be accepted for verification.
+.It Cm namespaces Ns = Ns "namespace-list"
+Specifies a pattern-list of namespaces that are accepted for this key.
+If this option is present, the signature namespace embedded in the
+signature object and presented on the verification command-line must
+match the specified list before the key will be considered acceptable.
+.It Cm valid-after Ns = Ns "timestamp"
+Indicates that the key is valid for use at or after the specified timestamp,
+which may be a date or time in the YYYYMMDD[Z] or YYYYMMDDHHMM[SS][Z] formats.
+Dates and times will be interpreted in the current system time zone unless
+suffixed with a Z character, which causes them to be interpreted in the UTC
+time zone.
+.It Cm valid-before Ns = Ns "timestamp"
+Indicates that the key is valid for use at or before the specified timestamp.
+.El
+.Pp
+When verifying signatures made by certificates, the expected principal
+name must match both the principals pattern in the allowed signers file and
+the principals embedded in the certificate itself.
+.Pp
+An example allowed signers file:
+.Bd -literal -offset 3n
+# Comments allowed at start of line
+user1@example.com,user2@example.com ssh-rsa AAAAX1...
+# A certificate authority, trusted for all principals in a domain.
+*@example.com cert-authority ssh-ed25519 AAAB4...
+# A key that is accepted only for file signing.
+user2@example.com namespaces="file" ssh-ed25519 AAA41...
+.Ed
+.Sh ENVIRONMENT
+.Bl -tag -width Ds
+.It Ev SSH_SK_PROVIDER
+Specifies a path to a library that will be used when loading any
+FIDO authenticator-hosted keys, overriding the default of using
+the built-in USB HID support.
+.El
+.Sh FILES
+.Bl -tag -width Ds -compact
+.It Pa ~/.ssh/id_dsa
+.It Pa ~/.ssh/id_ecdsa
+.It Pa ~/.ssh/id_ecdsa_sk
+.It Pa ~/.ssh/id_ed25519
+.It Pa ~/.ssh/id_ed25519_sk
+.It Pa ~/.ssh/id_rsa
+Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519,
+authenticator-hosted Ed25519 or RSA authentication identity of the user.
+This file should not be readable by anyone but the user.
+It is possible to
+specify a passphrase when generating the key; that passphrase will be
+used to encrypt the private part of this file using 128-bit AES.
+This file is not automatically accessed by
+.Nm
+but it is offered as the default file for the private key.
+.Xr ssh 1
+will read this file when a login attempt is made.
+.Pp
+.It Pa ~/.ssh/id_dsa.pub
+.It Pa ~/.ssh/id_ecdsa.pub
+.It Pa ~/.ssh/id_ecdsa_sk.pub
+.It Pa ~/.ssh/id_ed25519.pub
+.It Pa ~/.ssh/id_ed25519_sk.pub
+.It Pa ~/.ssh/id_rsa.pub
+Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519,
+authenticator-hosted Ed25519 or RSA public key for authentication.
+The contents of this file should be added to
+.Pa ~/.ssh/authorized_keys
+on all machines
+where the user wishes to log in using public key authentication.
+There is no need to keep the contents of this file secret.
+.Pp
+.It Pa /etc/ssh/moduli
+Contains Diffie-Hellman groups used for DH-GEX.
+The file format is described in
+.Xr moduli 5 .
+.El
+.Sh SEE ALSO
+.Xr ssh 1 ,
+.Xr ssh-add 1 ,
+.Xr ssh-agent 1 ,
+.Xr moduli 5 ,
+.Xr sshd 8
+.Rs
+.%R RFC 4716
+.%T "The Secure Shell (SSH) Public Key File Format"
+.%D 2006
+.Re
+.Sh AUTHORS
+OpenSSH is a derivative of the original and free
+ssh 1.2.12 release by Tatu Ylonen.
+Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
+Theo de Raadt and Dug Song
+removed many bugs, re-added newer features and
+created OpenSSH.
+Markus Friedl contributed the support for SSH
+protocol versions 1.5 and 2.0.