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 -U reader [-f input_keyfile]

DESCRIPTION
     ssh-keygen generates, manages and converts authentication keys for
     ssh(1). ssh-keygen defaults to generating a RSA1 key for use by SSH pro-
     tocol version 1.  Specifying the -t option instead creates a key for use
     by SSH protocol version 2.

     Normally each user wishing to use SSH with RSA or DSA authentication runs
     this once to create the authentication key in $HOME/.ssh/identity,
     $HOME/.ssh/id_dsa or $HOME/.ssh/id_rsa. Additionally, the system adminis-
     trator 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.  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 character, 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, 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:

     -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 the passphrase if the key has one, and for the new


             comment.

     -e      This option will read a private or public OpenSSH key file and
             print the key in a `SECSH Public Key File Format' to stdout.
             This option allows exporting keys for use by several commercial
             SSH implementations.

     -f filename
             Specifies the filename of the key file.

     -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 `SECSH
             Public Key File Format'. This option allows importing keys from
             several commercial SSH implementations.

     -l      Show fingerprint of specified private or public key file.

     -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.

     -y      This option will read a private OpenSSH format file and print an
             OpenSSH public key to stdout.

     -t type
             Specifies the type of the key to create.  The possible values are
             ``rsa1'' for protocol version 1 and ``rsa'' or ``dsa'' for proto-
             col version 2.  The default is ``rsa1''.

     -B      Show the bubblebabble digest of specified private or public key
             file.

     -C comment
             Provides the new comment.

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

     -N new_passphrase
             Provides the new passphrase.

     -P passphrase
             Provides the (old) passphrase.

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

FILES
     $HOME/.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.

     $HOME/.ssh/identity.pub
             Contains the protocol version 1 RSA public key for authentica-
             tion.  The contents of this file should be added to
             $HOME/.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.

     $HOME/.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.

     $HOME/.ssh/id_dsa.pub
             Contains the protocol version 2 DSA public key for authentica-
             tion.  The contents of this file should be added to
             $HOME/.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.

     $HOME/.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.

     $HOME/.ssh/id_rsa.pub
             Contains the protocol version 2 RSA public key for authentica-
             tion.  The contents of this file should be added to
             $HOME/.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.

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.

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

     J. Galbraith, and R. Thayer, SECSH Public Key File Format, draft-ietf-
     secsh-publickeyfile-01.txt, March 2001, work in progress material.

OpenBSD 3.0                   September 25, 1999                             3
