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

NAME
     ssh-keygen - authentication key generation



SYNOPSIS
     ssh-keygen [-q] [-b bits] [-N new_passphrase] [-C comment]
     ssh-keygen -p [-P old_passphrase] [-N new_passphrase]
     ssh-keygen -c [-P passphrase] [-C comment]

DESCRIPTION
     ssh-keygen generates and manages authentication keys for ssh(1).  Normal-
     ly each user wishing to use SSH with RSA authentication runs this once to
     create the authentication key in $HOME/.ssh/identity. 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
     empty passphrase), or it may be a string of arbitrary length.  Good
     passphrases are 10-30 characters long and are not simple sentences or
     otherwise easily guessable (English prose has only 1-2 bits of entropy
     per word, and provides very bad passphrases).  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, you will have to generate a new key and copy the corre-
     sponding public key to other machines.

     There is also a comment field in the key file that is only for conve-
     nience 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.

     The options are as follows:

     -b bits
             Specifies the number of bits in the key to create.  Minimum is
             512 bits.  Generally 1024 bits is considered sufficient, and key
             sizes above that no longer improve security but make things slow-
             er.  The default is 1024 bits.

     -c      Requests changing the comment in the private and public key
             files.  The program will prompt for the file containing the pri-
             vate keys, for passphrase if the key has one, and for the new
             comment.

     -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.

     -C comment
             Provides the new comment.

     -N new_passphrase
             Provides the new passphrase.

     -P passphrase
             Provides the (old) passphrase.

FILES
     $HOME/.ssh/random_seed
             Used for seeding the random number generator.  This file should
             not be readable by anyone but the user.  This file is created the
             first time the program is run, and is updated every time.

     $HOME/.ssh/identity
             Contains the 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.

     $HOME/.ssh/identity.pub
             Contains the public key for authentication.  The contents of this
             file should be added to $HOME/.ssh/authorized_keys on all ma-
             chines where you wish to log in using RSA authentication.  There
             is no need to keep the contents of this file secret.

AUTHOR
     Tatu Ylonen <ylo@cs.hut.fi>

     OpenSSH is a derivative of the original (free) ssh 1.2.12 release, but
     with bugs removed and newer features re-added.   Rapidly after the 1.2.12
     release, newer versions bore successively more restrictive licenses.
     This version of OpenSSH

     -   has all components of a restrictive nature (ie. patents, see ssl(8))
         directly removed from the source code; any licensed or patented com-
         ponents are chosen from external libraries.

     -   has been updated to support ssh protocol 1.5.

     -   contains added support for kerberos(8) authentication and ticket
         passing.

     -   supports one-time password authentication with skey(1).

     The libraries described in ssl(8) are required for proper operation.

SEE ALSO
     ssh(1),  ssh-add(1),  ssh-agent(1,) sshd(8),  ssl(8)

OpenBSD 2.6                   September 25, 1999                             2