ssh-keygen

     ssh-keygen [-q] [-b bits] [-t type] [-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 [-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 RSA keys for use by SSH protocol version 1
     and DSA, ECDSA, ED25519 or RSA 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 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     Lists, and to test whether given keys have been revoked by one.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 char-
     acters you want.  Good passphrases are 10-30 characters long, are not
     tell what the key is for, or whatever is useful.  The comment is initial-
     ized 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 comment.  This is used by system adminis-
             tration scripts to generate new host keys.

     -a rounds
             When saving a new-format private key (i.e. an ed25519 key or any
             SSH protocol 2 key when the -o flag is set), this option speci-
             fies 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 768 bits and the default is 2048 bits.  Gen-
             erally, 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.  The pro-
             gram 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).

     -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.

     -J num_lines
             Exit after screening the specified number of lines while perform-
             ing 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 perform-
             ing DH candidate screening using the -T option.  This will be
             used to skip lines in the input file that have already been pro-
             cessed if the job is restarted.  This option allows importing
             keys from other software, including several commercial SSH imple-
             mentations.  The default import format is ``RFC4716''.

     -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 a certificate.
             Specify a key format for the -i (import) or -e (export) conver-
             sion 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 princi-
             pals 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.  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 clear-
                     ing the default set of permissions so permissions may be
                     added individually.

             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.

             At present, no options are valid for host keys.

     -o      Causes ssh-keygen to save SSH protocol 2 private keys using the
             new OpenSSH format rather than the more compatible PEM format.
             The new format has increased resistance 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 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 type
             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 com-
             mand line are added to the existing KRL rather than a new KRL
             being created.


             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 midnight, January 1st,
             2011).

     -v      Verbose mode.  Causes ssh-keygen to print debugging messages
             about its progress.  This is helpful for debugging moduli genera-
             tion.  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 ver-
             sion 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 suitabil-
     ity (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 speci-
     fies 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
     (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 cer-
     tificates 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 pro-
     viding 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 host_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 princi-
     pals:

           $ 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 user_key.pub

     Additional limitations on the validity and use of user certificates may
     be specified through certificate options.  A certificate option may dis-
     able 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 cer-
     tificate that is presented at a time outside this range will not be con-
     sidered 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 pub-
     lic key must be trusted by sshd(8) or ssh(1).  Please refer to those man-
     ual pages for details.

KEY REVOCATION LISTS
     ssh-keygen is able to manage OpenSSH format Key Revocation Lists (KRLs).
     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 orig-
     inal certificate on hand.  A KRL specification consists of lines contain-
     ing one of the following directives followed by a colon and some direc-
     tive-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 commandline.  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 authentica-
             tion.  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.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 Ylonen.  Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
     de Raadt and Dug Song removed many bugs, re-added newer features and cre-
     ated OpenSSH.  Markus Friedl contributed the support for SSH protocol
     versions 1.5 and 2.0.

BSD                           September 21, 2018                           BSD
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