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SSH-KEYGEN(1)              OpenBSD Reference Manual              SSH-KEYGEN(1)

NAME

     ssh-keygen - authentication key generation, management and conversion

SYNOPSIS

     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 [-f input_keyfile]

     ssh-keygen -e [-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 reader

     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 -U reader [-f input_keyfile]

     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] [-W

                generator]

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 RSA or DSA 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.

     Normally each user wishing to use SSH with RSA or DSA authentication runs

     this once to create the authentication key in ~/.ssh/identity,

     ~/.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 se-

     ries of words, punctuation, numbers, whitespace, or any string of charac-

     ters you want.  Good passphrases are 10-30 characters long, are not sim-

     ple 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-alphanu-

     meric 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 copied to the corresponding

     public key 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 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 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.  Gen-

             erally, 2048 bits is considered sufficient.  DSA keys must be ex-

             actly 1024 bits as specified by FIPS 186-2.

     -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 reader

             Download the RSA public key stored in the smartcard in reader.

     -e      This option will read a private or public OpenSSH key file and

             print the key in RFC 4716 SSH Public Key File Format to stdout.

             This option allows exporting keys for use by 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 ad-

             dresses 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.

     -i      This option will read an unencrypted private (or public) key file

             in SSH2-compatible format and print an OpenSSH compatible private

             (or public) key to stdout.  ssh-keygen also reads the RFC 4716

             SSH Public Key File Format.  This option allows importing keys

             from several commercial SSH implementations.

     -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 sup-

             plied with the fingerprint.

     -M memory

             Specify the amount of memory to use (in megabytes) when generat-

             ing candidate moduli for DH-GEX.

     -N new_passphrase

             Provides the new passphrase.

     -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      Silence ssh-keygen.  Used by /etc/rc when creating a new key.

     -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.

     -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 ``rsa'' or ``dsa'' for proto-

             col version 2.

     -U reader

             Upload an existing RSA private key into the smartcard in reader.

     -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.

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 pro-

     cess: first, candidate primes are generated using a fast, but memory in-

     tensive 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 speci-

     fies a different start point (in hex).

     Once a set of candidates have been generated, they must be tested for

     suitability.  This may be performed using the -T option.  In this mode

     ssh-keygen will read candidates from standard input (or a file specified

     using the -f option).  For example:

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

     By default, each candidate will be subjected to 100 primality tests.

     This may be overridden using the -a option.  The DH generator value will

     be chosen automatically for the prime under consideration.  If a specific

     generator is desired, it may be requested using the -W option.  Valid

     generator values are 2, 3, and 5.

     Screened DH groups may be installed in /etc/moduli.  It is important that

     this file contains moduli of a range of bit lengths and that both ends of

     a connection share common moduli.

FILES

     ~/.ssh/identity

             Contains the protocol version 1 RSA authentication identity of

             the user.  This file should not be readable by anyone but the us-

             er.  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

             Contains the protocol version 2 DSA authentication identity of

             the user.  This file should not be readable by anyone but the us-

             er.  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/id_dsa.pub

             Contains the protocol version 2 DSA 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 public key authentication.  There is no need to keep

             the contents of this file secret.

     ~/.ssh/id_rsa

             Contains the protocol version 2 RSA authentication identity of

             the user.  This file should not be readable by anyone but the us-

             er.  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/id_rsa.pub

             Contains the protocol version 2 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 public key authentication.  There is no need to keep

             the contents of this file secret.

     /etc/moduli

             Contains Diffie-Hellman groups used for DH-GEX.  The file format

             is described in moduli(5).

SEE ALSO

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

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

AUTHORS

     OpenSSH is a derivative of the original and free ssh 1.2.12 release by

     Tatu Ylonen.  Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo

     de Raadt and Dug Song removed many bugs, re-added newer features and

     created OpenSSH.  Markus Friedl contributed the support for SSH protocol

     versions 1.5 and 2.0.

OpenBSD 4.6                      July 24, 2008                               5