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

NAME
     ssh-keygen — authentication key generation, management and conversion

SYNOPSIS
     ssh-keygen [-q] [-b bits] [-t dsa | ecdsa | ed25519 | rsa | rsa1]
                [-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] [-n principals] [-O option]
                [-V validity_interval] [-z serial_number] file ...
     ssh-keygen -L [-f input_keyfile]
     ssh-keygen -A
     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 versions 1 and 2.  Protocol 1
     should not be used and is only offered to support legacy devices.  It suffers from
     a number of cryptographic weaknesses and doesn't support many of the advanced fea‐
     tures available for protocol 2.

     The type of key to be generated is specified with the -t option.  If invoked with‐
     out any arguments, ssh-keygen will generate an RSA key for use in SSH protocol 2
     connections.

     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     to test whether given keys have been revoked by one.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/identity, ~/.ssh/id_dsa,
     ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 or ~/.ssh/id_rsa.  Additionally, the system
     administrator may use this to generate host keys.

     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 “.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 -p option.

     There is no way to recover a lost passphrase.  If the passphrase is lost or for‐
     gotten, a new key must be generated and the corresponding public key copied to
     other machines.

     For RSA1 keys and 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 “user@host” 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 (rsa1, 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 com‐
             ment.  This is used by system administration scripts to generate new host
             keys.

     -a rounds
             When saving a new-format private key (i.e. an ed25519 key or any SSH pro‐
             tocol 2 key when the -o flag is set), 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 min‐
             imum 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.  This
             operation is only supported for RSA1 keys and keys stored in the newer
             OpenSSH format.  The program will prompt for the file containing the pri‐
             vate 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: “md5” and “sha256”.  The default is “sha256”.

     -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 “RFC4716”.  This option allows exporting OpenSSH
             keys for use by other programs, including several commercial SSH implemen‐
             tations.

     -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 certifi‐
             cate.  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 “RFC4716”.

     -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 can‐
             didate 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 certifi‐
             cate 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.  Private RSA1 keys are also
             supported.  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 candi‐
             date 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: “RFC4716” (RFC 4716/SSH2 public
             or private key), “PKCS8” (PEM PKCS8 public key) or “PEM” (PEM public key).
             The default conversion format is “RFC4716”.

     -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 spec‐
             ified multiple times.  Please see the CERTIFICATES section for details.
             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 individu‐
                     ally.

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

             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 con‐
                     sidered valid.  The address_list is a comma-separated list of one
                     or more address/netmask pairs in CIDR format.

             At present, no options are valid for host keys.

     -o      Causes ssh-keygen to save private keys using the new OpenSSH format rather
             than the more compatible PEM format.  The new format has increased resis‐
             tance to brute-force password cracking but is not supported by versions of
             OpenSSH prior to 6.5.  Ed25519 keys always use the new private key 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 speci‐
             fied 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 | rsa1
             Specifies the type of key to create.  The possible values are “rsa1” for
             protocol version 1 and “dsa”, “ecdsa”, “ed25519”, or “rsa” for protocol
             version 2.

     -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 inter‐
             val 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 sepa‐
             rated by a colon to indicate an explicit time interval.  The start time
             may be specified as a date in YYYYMMDD format, a time in YYYYMMDDHHMMSS
             format or a relative time (to the current time) consisting of a minus sign
             followed by a relative time in the format described in the TIME FORMATS
             section of sshd_config(5).  The end time may be specified as a YYYYMMDD
             date, a YYYYMMDDHHMMSS time or a relative time starting with a plus char‐
             acter.

             For example: “+52w1d” (valid from now to 52 weeks and one day from now),
             “-4w:+4w” (valid from four weeks ago to four weeks from now),
             “20100101123000:20110101123000” (valid from 12:30 PM, January 1st, 2010 to
             12:30 PM, January 1st, 2011), “-1d:20110101” (valid from yesterday to mid‐
             night, January 1st, 2011).

     -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 num‐
             ber.

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, candi‐
     date primes are generated using a fast, but memory intensive process.  These can‐
     didate 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 suitabil‐
     ity.  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 automati‐
     cally 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/ssh/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 trust‐
     ing 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

     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 speci‐
     fied 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 its SHA1 hash.

     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/identity
             Contains the protocol version 1 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 3DES.  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/identity.pub
             Contains the protocol version 1 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 RSA authentication.  There
             is no need to keep the contents of this file secret.

     ~/.ssh/id_dsa
     ~/.ssh/id_ecdsa
     ~/.ssh/id_ed25519
     ~/.ssh/id_rsa
             Contains the protocol version 2 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 protocol version 2 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/ssh/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 Ylo‐
     nen.  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.

BSD                                  June 16, 2016                                  BSD

usage: ssh-keygen [-q] [-b bits] [-t dsa | ecdsa | ed25519 | rsa | rsa1]
                  [-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] [-n principals]
                  [-O option] [-V validity_interval] [-z serial_number] file ...
       ssh-keygen -L [-f input_keyfile]
       ssh-keygen -A
       ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number]
                  file ...
       ssh-keygen -Q -f krl_file file ...