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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]
     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.

     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 $HOME/.ssh/identity,
     $HOME/.ssh/id_dsa or $HOME/.ssh/id_rsa.  Additionally, the system admin-
     istrator 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 char-
     acters you want.  Good passphrases are 10-30 characters long, are not
     simple 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-
     alphanumeric 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.
	     DH-GEX candidates using the -T command.

     -b bits
	     Specifies the number of bits in the key to create.  Minimum is
	     512 bits.	Generally, 1024 bits is considered sufficient.	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.

     -g      Use generic DNS resource record format.

     -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.

     -G output_file
	     Generate candidate primes for DH-GEX.  These primes must be

     -P passphrase
	     Provides the (old) passphrase.

     -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.

     -W generator
	     Specify desired generator when testing candidate moduli for DH-
	     GEX.

     -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.

     -r hostname
	     Print DNS resource record with the specified hostname.

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
     process: first, candidate primes are generated using a fast, but memory
     intensive process.  These candidate primes are then tested for suitabil-
     ity (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
	     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
	     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.

     $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
	     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.

     $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.

     /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)

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

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

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