path: root/ssh-keygen.0

SSH-KEYGEN(1)               General Commands Manual              SSH-KEYGEN(1)

NAME
     ssh-keygen M-bM-^@M-^S authentication key generation, management and conversion

SYNOPSIS
     ssh-keygen [-q] [-b bits] [-t dsa | ecdsa | ed25519 | rsa]
                [-N new_passphrase] [-C comment] [-f output_keyfile]
     ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile]
     ssh-keygen -i [-m key_format] [-f input_keyfile]
     ssh-keygen -e [-m key_format] [-f input_keyfile]
     ssh-keygen -y [-f input_keyfile]
     ssh-keygen -c [-P passphrase] [-C comment] [-f keyfile]
     ssh-keygen -l [-v] [-E fingerprint_hash] [-f input_keyfile]
     ssh-keygen -B [-f input_keyfile]
     ssh-keygen -D pkcs11
     ssh-keygen -F hostname [-f known_hosts_file] [-l]
     ssh-keygen -H [-f known_hosts_file]
     ssh-keygen -R hostname [-f known_hosts_file]
     ssh-keygen -r hostname [-f input_keyfile] [-g]
     ssh-keygen -G output_file [-v] [-b bits] [-M memory] [-S start_point]
     ssh-keygen -T output_file -f input_file [-v] [-a rounds] [-J num_lines]
                [-j start_line] [-K checkpt] [-W generator]
     ssh-keygen -s ca_key -I certificate_identity [-h] [-U]
                [-D pkcs11_provider] [-n principals] [-O option]
                [-V validity_interval] [-z serial_number] file ...
     ssh-keygen -L [-f input_keyfile]
     ssh-keygen -A [-f prefix_path]
     ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number]
                file ...
     ssh-keygen -Q -f krl_file file ...

DESCRIPTION
     ssh-keygen generates, manages and converts authentication keys for
     ssh(1).  ssh-keygen can create keys for use by SSH protocol version 2.

     The type of key to be generated is specified with the -t option.  If
     invoked without any arguments, ssh-keygen will generate an RSA key.

     ssh-keygen is also used to generate groups for use in Diffie-Hellman
     group exchange (DH-GEX).  See the MODULI GENERATION section for details.

     Finally, ssh-keygen can be used to generate and update Key Revocation
     Lists, and to test whether given keys have been revoked by one.  See the
     KEY REVOCATION LISTS section for details.

     Normally each user wishing to use SSH with public key authentication runs
     this once to create the authentication key in ~/.ssh/id_dsa,
     ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 or ~/.ssh/id_rsa.  Additionally, the
     system administrator may use this to generate host keys, as seen in
     /etc/rc.

     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 M-bM-^@M-^\.pubM-bM-^@M-^] 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 -p option.

     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.

     For keys stored in the newer OpenSSH format, there is also a comment
     field in the key file that is only for convenience to the user to help
     identify the key.  The comment can tell what the key is for, or whatever
     is useful.  The comment is initialized to M-bM-^@M-^\user@hostM-bM-^@M-^] when the key is
     created, but can be changed using the -c option.

     After a key is generated, instructions below detail where the keys should
     be placed to be activated.

     The options are as follows:

     -A      For each of the key types (rsa, dsa, ecdsa and ed25519) for which
             host keys do not exist, generate the host keys with the default
             key file path, an empty passphrase, default bits for the key
             type, and default comment.  If -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 /etc/rc to generate
             new host keys.

     -a rounds
             When saving a private key this option specifies the number of KDF
             (key derivation function) rounds used.  Higher numbers result in
             slower passphrase verification and increased resistance to brute-
             force password cracking (should the keys be stolen).

             When screening DH-GEX candidates (using the -T command).  This
             option specifies the number of primality tests to perform.

     -B      Show the bubblebabble digest of specified private or public key
             file.

     -b bits
             Specifies the number of bits in the key to create.  For RSA keys,
             the minimum size is 1024 bits and the default is 2048 bits.
             Generally, 2048 bits is considered sufficient.  DSA keys must be
             exactly 1024 bits as specified by FIPS 186-2.  For ECDSA keys,
             the -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.  Ed25519 keys have a fixed length and the -b flag will be
             ignored.

     -C comment
             Provides a new comment.

     -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.

     -D pkcs11
             Download the RSA public keys provided by the PKCS#11 shared
             library pkcs11.  When used in combination with -s, this option
             indicates that a CA key resides in a PKCS#11 token (see the
             CERTIFICATES section for details).

     -E fingerprint_hash
             Specifies the hash algorithm used when displaying key
             fingerprints.  Valid options are: M-bM-^@M-^\md5M-bM-^@M-^] and M-bM-^@M-^\sha256M-bM-^@M-^].  The
             default is M-bM-^@M-^\sha256M-bM-^@M-^].

     -e      This option will read a private or public OpenSSH key file and
             print to stdout the key in one of the formats specified by the -m
             option.  The default export format is M-bM-^@M-^\RFC4716M-bM-^@M-^].  This option
             allows exporting OpenSSH keys for use by other programs,
             including several commercial SSH implementations.

     -F hostname
             Search for the specified hostname in a 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
             -H option to print found keys in a hashed format.

     -f filename
             Specifies the filename of the key file.

     -G output_file
             Generate candidate primes for DH-GEX.  These primes must be
             screened for safety (using the -T option) before use.

     -g      Use generic DNS format when printing fingerprint resource records
             using the -r command.

     -H      Hash a 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 ssh and 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.

     -h      When signing a key, create a host certificate instead of a user
             certificate.  Please see the CERTIFICATES section for details.

     -I certificate_identity
             Specify the key identity when signing a public key.  Please see
             the CERTIFICATES section for details.

     -i      This option will read an unencrypted private (or public) key file
             in the format specified by the -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 M-bM-^@M-^\RFC4716M-bM-^@M-^].

     -J num_lines
             Exit after screening the specified number of lines while
             performing DH candidate screening using the -T option.

     -j start_line
             Start screening at the specified line number while performing DH
             candidate screening using the -T option.

     -K checkpt
             Write the last line processed to the file checkpt while
             performing DH candidate screening using the -T option.  This will
             be used to skip lines in the input file that have already been
             processed if the job is restarted.

     -k      Generate a KRL file.  In this mode, ssh-keygen will generate a
             KRL file at the location specified via the -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 KEY REVOCATION LISTS
             section.

     -L      Prints the contents of one or more certificates.

     -l      Show fingerprint of specified public key file.  For RSA and DSA
             keys ssh-keygen tries to find the matching public key file and
             prints its fingerprint.  If combined with -v, a visual ASCII art
             representation of the key is supplied with the fingerprint.

     -M memory
             Specify the amount of memory to use (in megabytes) when
             generating candidate moduli for DH-GEX.

     -m key_format
             Specify a key format for the -i (import) or -e (export)
             conversion options.  The supported key formats are: M-bM-^@M-^\RFC4716M-bM-^@M-^]
             (RFC 4716/SSH2 public or private key), M-bM-^@M-^\PKCS8M-bM-^@M-^] (PEM PKCS8 public
             key) or M-bM-^@M-^\PEMM-bM-^@M-^] (PEM public key).  The default conversion format is
             M-bM-^@M-^\RFC4716M-bM-^@M-^].  Setting a format of M-bM-^@M-^\PEMM-bM-^@M-^] when generating or updating
             a supported private key type will cause the key to be stored in
             the legacy PEM private key format.

     -N new_passphrase
             Provides the new passphrase.

     -n 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.  Please see the
             CERTIFICATES section for details.

     -O option
             Specify a certificate option when signing a key.  This option may
             be specified multiple times.  See also the CERTIFICATES section
             for further details.

             At present, no standard options are valid for host keys.  The
             options that are valid for user certificates are:

             clear   Clear all enabled permissions.  This is useful for
                     clearing the default set of permissions so permissions
                     may be added individually.

             critical:name[=contents]
             extension:name[=contents]
                     Includes an arbitrary certificate critical option or
                     extension.  The specified name should include a domain
                     suffix, e.g. M-bM-^@M-^\name@example.comM-bM-^@M-^].  If 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.

             force-command=command
                     Forces the execution of command instead of any shell or
                     command specified by the user when the certificate is
                     used for authentication.

             no-agent-forwarding
                     Disable ssh-agent(1) forwarding (permitted by default).

             no-port-forwarding
                     Disable port forwarding (permitted by default).

             no-pty  Disable PTY allocation (permitted by default).

             no-user-rc
                     Disable execution of ~/.ssh/rc by sshd(8) (permitted by
                     default).

             no-x11-forwarding
                     Disable X11 forwarding (permitted by default).

             permit-agent-forwarding
                     Allows ssh-agent(1) forwarding.

             permit-port-forwarding
                     Allows port forwarding.

             permit-pty
                     Allows PTY allocation.

             permit-user-rc
                     Allows execution of ~/.ssh/rc by sshd(8).

             permit-X11-forwarding
                     Allows X11 forwarding.

             source-address=address_list
                     Restrict the source addresses from which the certificate
                     is considered valid.  The address_list is a comma-
                     separated list of one or more address/netmask pairs in
                     CIDR format.

     -P passphrase
             Provides the (old) passphrase.

     -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.

     -Q      Test whether keys have been revoked in a KRL.

     -q      Silence ssh-keygen.

     -R hostname
             Removes all keys belonging to hostname from a known_hosts file.
             This option is useful to delete hashed hosts (see the -H option
             above).

     -r hostname
             Print the SSHFP fingerprint resource record named hostname for
             the specified public key file.

     -S start
             Specify start point (in hex) when generating candidate moduli for
             DH-GEX.

     -s ca_key
             Certify (sign) a public key using the specified CA key.  Please
             see the CERTIFICATES section for details.

             When generating a KRL, -s specifies a path to a CA public key
             file used to revoke certificates directly by key ID or serial
             number.  See the KEY REVOCATION LISTS section for details.

     -T output_file
             Test DH group exchange candidate primes (generated using the -G
             option) for safety.

     -t dsa | ecdsa | ed25519 | rsa
             Specifies the type of key to create.  The possible values are
             M-bM-^@M-^\dsaM-bM-^@M-^], M-bM-^@M-^\ecdsaM-bM-^@M-^], M-bM-^@M-^\ed25519M-bM-^@M-^], or M-bM-^@M-^\rsaM-bM-^@M-^].

     -U      When used in combination with -s, this option indicates that a CA
             key resides in a ssh-agent(1).  See the CERTIFICATES section for
             more information.

     -u      Update a KRL.  When specified with -k, keys listed via the
             command line are added to the existing KRL rather than a new KRL
             being created.

     -V 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.

             The start time may be specified as the string M-bM-^@M-^\alwaysM-bM-^@M-^] to
             indicate the certificate has no specified start time, a date in
             YYYYMMDD format, a time in YYYYMMDDHHMM[SS] format, a relative
             time (to the current time) consisting of a minus sign followed by
             an interval in the format described in the TIME FORMATS section
             of sshd_config(5).

             The end time may be specified as a YYYYMMDD date, a
             YYYYMMDDHHMM[SS] time, a relative time starting with a plus
             character or the string M-bM-^@M-^\foreverM-bM-^@M-^] to indicate that the
             certificate has no expirty date.

             For example: M-bM-^@M-^\+52w1dM-bM-^@M-^] (valid from now to 52 weeks and one day
             from now), M-bM-^@M-^\-4w:+4wM-bM-^@M-^] (valid from four weeks ago to four weeks
             from now), M-bM-^@M-^\20100101123000:20110101123000M-bM-^@M-^] (valid from 12:30 PM,
             January 1st, 2010 to 12:30 PM, January 1st, 2011), M-bM-^@M-^\-1d:20110101M-bM-^@M-^]
             (valid from yesterday to midnight, January 1st, 2011).
             M-bM-^@M-^\-1m:foreverM-bM-^@M-^] (valid from one minute ago and never expiring).

     -v      Verbose mode.  Causes ssh-keygen to print debugging messages
             about its progress.  This is helpful for debugging moduli
             generation.  Multiple -v options increase the verbosity.  The
             maximum is 3.

     -W generator
             Specify desired generator when testing candidate moduli for DH-
             GEX.

     -y      This option will read a private OpenSSH format file and print an
             OpenSSH public key to stdout.

     -z serial_number
             Specifies a serial number to be embedded in the certificate to
             distinguish this certificate from others from the same CA.  The
             default serial number is zero.

             When generating a KRL, the -z flag is used to specify a KRL
             version number.

MODULI GENERATION
     ssh-keygen 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).

     Generation of primes is performed using the -G option.  The desired
     length of the primes may be specified by the -b option.  For example:

           # ssh-keygen -G moduli-2048.candidates -b 2048

     By default, the search for primes begins at a random point in the desired
     length range.  This may be overridden using the -S option, which
     specifies a different start point (in hex).

     Once a set of candidates have been generated, they must be screened for
     suitability.  This may be performed using the -T option.  In this mode
     ssh-keygen will read candidates from standard input (or a file specified
     using the -f option).  For example:

           # ssh-keygen -T moduli-2048 -f moduli-2048.candidates

     By default, each candidate will be subjected to 100 primality tests.
     This may be overridden using the -a 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 -W option.  Valid
     generator values are 2, 3, and 5.

     Screened DH groups may be installed in /etc/moduli.  It is important that
     this file contains moduli of a range of bit lengths and that both ends of
     a connection share common moduli.

CERTIFICATES
     ssh-keygen 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 ssl(8).

     ssh-keygen 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:

           $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub

     The resultant certificate will be placed in /path/to/user_key-cert.pub.
     A host certificate requires the -h option:

           $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub

     The host certificate will be output to /path/to/host_key-cert.pub.

     It is possible to sign using a CA key stored in a PKCS#11 token by
     providing the token library using -D and identifying the CA key by
     providing its public half as an argument to -s:

           $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub

     Similarly, it is possible for the CA key to be hosted in a ssh-agent(1).
     This is indicated by the -U flag and, again, the CA key must be
     identified by its public half.

           $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub

     In all cases, key_id is a "key identifier" that is logged by the server
     when the certificate is used for authentication.

     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:

           $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
           $ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub

     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.  For a list of valid certificate options, see the documentation
     for the -O option above.

     Finally, certificates may be defined with a validity lifetime.  The -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 UNIX Epoch to
     the distant future.

     For certificates to be used for user or host authentication, the CA
     public key must be trusted by sshd(8) or ssh(1).  Please refer to those
     manual pages for details.

KEY REVOCATION LISTS
     ssh-keygen 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.

     KRLs may be generated using the -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).

     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.

     serial: serial_number[-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 ssh-keygen command line using the -s option.

     id: key_id
             Revokes a certificate with the specified key ID string.  The CA
             key must have been specified on the ssh-keygen command line using
             the -s option.

     key: public_key
             Revokes the specified key.  If a certificate is listed, then it
             is revoked as a plain public key.

     sha1: public_key
             Revokes the specified key by including its SHA1 hash in the KRL.

     sha256: 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.

     hash: fingerprint
             Revokes a key using a fingerprint hash, as obtained from a
             sshd(8) authentication log message or the ssh-keygen -l flag.
             Only SHA256 fingerprints are supported here and resultant KRLs
             are not supported by OpenSSH versions prior to 7.9.

     KRLs may be updated using the -u flag in addition to -k.  When this
     option is specified, keys listed via the command line are merged into the
     KRL, adding to those already there.

     It is also possible, given a KRL, to test whether it revokes a particular
     key (or keys).  The -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 ssh-keygen will exit with a
     non-zero exit status.  A zero exit status will only be returned if no key
     was revoked.

FILES
     ~/.ssh/id_dsa
     ~/.ssh/id_ecdsa
     ~/.ssh/id_ed25519
     ~/.ssh/id_rsa
             Contains the DSA, ECDSA, 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 ssh-keygen but it is offered as the default file for
             the private key.  ssh(1) will read this file when a login attempt
             is made.

     ~/.ssh/id_dsa.pub
     ~/.ssh/id_ecdsa.pub
     ~/.ssh/id_ed25519.pub
     ~/.ssh/id_rsa.pub
             Contains the DSA, ECDSA, Ed25519 or RSA public key for
             authentication.  The contents of this file should be added to
             ~/.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.

     /etc/moduli
             Contains Diffie-Hellman groups used for DH-GEX.  The file format
             is described in moduli(5).

SEE ALSO
     ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)

     The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006.

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.

OpenBSD 6.4                   September 12, 2018                   OpenBSD 6.4