Mac Developer Library Developer


This manual page is for Mac OS X version 10.9

If you are running a different version of Mac OS X, view the documentation locally:

  • In Terminal, using the man(1) command

Reading manual pages

Manual pages are intended as a quick reference for people who already understand a technology.

  • To learn how the manual is organized or to learn about command syntax, read the manual page for manpages(5).

  • For more information about this technology, look for other documentation in the Apple Developer Library.

  • For general information about writing shell scripts, read Shell Scripting Primer.

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

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

     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 num_trials] [-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 RSA
     keys for use by SSH protocol version 1 and DSA, ECDSA 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_ecdsa, ~/.ssh/id_dsa 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 ``.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 charac-ters characters
     ters you want.  Good passphrases are 10-30 characters long, are not simple sentences or otherwise eas-ily easily
     ily 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 charac-ters. characters.
     ters.  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, 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 com-ment comment
     ment 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 and ecdsa) 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 /etc/rc to generate new host keys.

     -a trials
             Specifies the number of primality tests to perform when screening DH-GEX candidates using the
             -T command.

     -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.  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.

     -C comment
             Provides a new comment.

     -c      Requests changing the comment in the private and public key files.  This operation is only sup-ported supported
             ported for RSA1 keys.  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 com-bination combination
             bination with -s, this option indicates that a CA key resides in a PKCS#11 token (see the
             CERTIFICATES section for details).

     -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

     -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 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 pro-cessed processed
             cessed if the job is restarted.  This option allows importing keys from other software, includ-ing including
             ing several commercial SSH implementations.  The default import format is ``RFC4716''.

     -k      Generate a KRL file.  In this mode, ssh-keygen will generate a KRL file at the location speci-fied specified
             fied 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.

     -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, an 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 ``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 sign-ing signing
             ing 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 certifi-cates certificates
             cates are:

             clear   Clear all enabled permissions.  This is useful for clearing the default set of permis-sions permissions
                     sions 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 default).

                     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

             At present, no options are valid for host keys.

     -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'' or ``rsa'' for protocol version 2.

     -u      Update a KRL.  When specified with -k, keys listed via the command line are added to the exist-ing existing
             ing 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 speci-fied specified
             fied as a YYYYMMDD date, a YYYYMMDDHHMMSS time or a relative time starting with a plus charac-ter. 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 yes-terday yesterday
             terday to midnight, January 1st, 2011).

     -v      Verbose mode.  Causes ssh-keygen to print debugging messages about its progress.  This is help-ful helpful
             ful 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.

     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

     Generation of primes is performed using the -G option.  The desired length of the primes may be speci-fied specified
     fied 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 per-formed performed
     formed 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.

     ssh-keygen supports signing of keys to produce certificates that may be used for user or host authenti-cation. authentication.
     cation.  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, gener-ated generated
     ated 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 certifi-cate certificate
     cate 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 a 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 com-plete complete
     plete original certificate on hand.  A KRL specification consists of lines containing one of the fol-lowing following
     lowing 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 speci-fied specified
             fied 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

     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

     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.

             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 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 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

             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

BSD                            October 11, 2013                            BSD

Reporting Problems

The way to report a problem with this manual page depends on the type of problem:

Content errors
Report errors in the content of this documentation to the OpenSSH project.
Bug reports
Report bugs in the functionality of the described tool or API to Apple through Bug Reporter and to the OpenSSH project through their bug reporting page.
Formatting problems
Report formatting mistakes in the online version of these pages with the feedback links below.