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


     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 ...


     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 features available for protocol 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     Lists, and to test whether given keys have been revoked by one.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

     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 forgotten, 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 comment.  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 protocol 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

     -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

     -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 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: "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 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 "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 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

     -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 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: "RFC4716"
         (RFC 4716/SSH2 public or private key), "PKCS8" (PEM PKCS8 public
         key) or "PEM" (PEM public key).  The default conversion format is

     -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.  Please see the CERTIFICATES section
         for details.  The options that are valid for user certificates

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

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

                 Disable ssh-agent(1) forwarding (permitted by default).

                 Disable port forwarding (permitted by default).

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

                 Disable execution of ~/.ssh/rc by sshd(8) (permitted by

                 Disable X11 forwarding (permitted by default).

                 Allows ssh-agent(1) forwarding.

                 Allows port forwarding.

                 Allows PTY allocation.

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

                 Allows X11 forwarding.

                 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.

         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 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

     -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

     -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 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 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 character.

         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
         generation.  Multiple -v options increase the verbosity.  The
         maximum is 3.

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

     -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.


     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/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.


     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/

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

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

     The host certificate will be output to /path/to/

     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 -D -I key_id

     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

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

     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.


     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.


         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.

         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.

         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.

         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.

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


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

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


     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.


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