Manual Pages: ssh-keygen

## Manual Pages

    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 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.

         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.  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:

         -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.  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.

         -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 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.

         -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.

         -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 3.1                   September 25, 1999                             3

NAME | SYNOPSIS | DESCRIPTION | FILES | AUTHORS | SEE ALSO