-.\" $OpenBSD: ssh-keygen.1,v 1.53 2002/02/16 14:53:37 stevesk Exp $
+.\" $OpenBSD: ssh-keygen.1,v 1.61 2003/12/22 09:16:58 djm Exp $
.\"
.\" -*- nroff -*-
.\"
.Nd authentication key generation, management and conversion
.Sh SYNOPSIS
.Nm ssh-keygen
+.Bk -words
.Op Fl q
.Op Fl b Ar bits
.Fl t Ar type
.Op Fl N Ar new_passphrase
.Op Fl C Ar comment
.Op Fl f Ar output_keyfile
+.Ek
.Nm ssh-keygen
.Fl p
.Op Fl P Ar old_passphrase
.Nm ssh-keygen
.Fl U Ar reader
.Op Fl f Ar input_keyfile
+.Nm ssh-keygen
+.Fl r Ar hostname
+.Op Fl f Ar input_keyfile
+.Op Fl g
+.Nm ssh-keygen
+.Fl G Ar output_file
+.Op Fl v
+.Op Fl b Ar bits
+.Op Fl M Ar memory
+.Op Fl S Ar start_point
+.Nm ssh-keygen
+.Fl T Ar output_file
+.Fl f Ar input_file
+.Op Fl v
+.Op Fl a Ar num_trials
+.Op Fl W Ar generator
.Sh DESCRIPTION
.Nm
generates, manages and converts authentication keys for
.Xr ssh 1 .
.Nm
-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
+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
.Fl t
option.
.Pp
+.Nm
+is also used to generate groups for use in Diffie-Hellman group
+exchange (DH-GEX).
+See the
+.Sx MODULI GENERATION
+section for details.
+.Pp
Normally each user wishing to use SSH
with RSA or DSA authentication runs this once to create the authentication
key in
.Pp
The options are as follows:
.Bl -tag -width Ds
+.It Fl a Ar trials
+Specifies the number of primality tests to perform when screening DH-GEX
+candidates using the
+.Fl T
+command.
.It Fl b Ar 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 slower.
+Generally, 1024 bits is considered sufficient.
The default is 1024 bits.
.It Fl c
Requests changing the comment in the private and public key files.
to stdout.
This option allows exporting keys for use by several commercial
SSH implementations.
+.It Fl g
+Use generic DNS resource record format.
.It Fl f Ar filename
Specifies the filename of the key file.
.It Fl i
.It Fl D Ar reader
Download the RSA public key stored in the smartcard in
.Ar reader .
+.It Fl G Ar output_file
+Generate candidate primes for DH-GEX.
+These primes must be screened for
+safety (using the
+.Fl T
+option) before use.
+.It Fl M Ar memory
+Specify the amount of memory to use (in megabytes) when generating
+candidate moduli for DH-GEX.
.It Fl N Ar new_passphrase
Provides the new passphrase.
.It Fl P Ar passphrase
Provides the (old) passphrase.
+.It Fl S Ar start
+Specify start point (in hex) when generating candidate moduli for DH-GEX.
+.It Fl T Ar output_file
+Test DH group exchange candidate primes (generated using the
+.Fl G
+option) for safety.
+.It Fl W Ar generator
+Specify desired generator when testing candidate moduli for DH-GEX.
.It Fl U Ar reader
Upload an existing RSA private key into the smartcard in
.Ar reader .
+.It Fl v
+Verbose mode.
+Causes
+.Nm
+to print debugging messages about its progress.
+This is helpful for debugging moduli generation.
+Multiple
+.Fl v
+options increase the verbosity.
+The maximum is 3.
+.It Fl r Ar hostname
+Print DNS resource record with the specified
+.Ar hostname .
.El
+.Sh MODULI GENERATION
+.Nm
+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 suitability (a CPU-intensive
+process).
+.Pp
+Generation of primes is performed using the
+.Fl G
+option.
+The desired length of the primes may be specified by the
+.Fl b
+option.
+For example:
+.Pp
+.Dl ssh-keygen -G moduli-2048.candidates -b 2048
+.Pp
+By default, the search for primes begins at a random point in the
+desired length range.
+This may be overridden using the
+.Fl S
+option, which specifies a different start point (in hex).
+.Pp
+Once a set of candidates have been generated, they must be tested for
+suitability.
+This may be performed using the
+.Fl T
+option.
+In this mode
+.Nm
+will read candidates from standard input (or a file specified using the
+.Fl f
+option).
+For example:
+.Pp
+.Dl ssh-keygen -T moduli-2048 -f moduli-2048.candidates
+.Pp
+By default, each candidate will be subjected to 100 primality tests.
+This may be overridden using the
+.Fl 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
+.Fl W
+option.
+Valid generator values are 2, 3 and 5.
+.Pp
+Screened DH groups may be installed in
+.Pa /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.
.Sh FILES
.Bl -tag -width Ds
.It Pa $HOME/.ssh/identity
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.
+.It Pa /etc/moduli
+Contains Diffie-Hellman groups used for DH-GEX.
+The file format is described in
+.Xr moduli 5 .
.El
-.Sh 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.
.Sh SEE ALSO
.Xr ssh 1 ,
.Xr ssh-add 1 ,
.Xr ssh-agent 1 ,
+.Xr moduli 5 ,
.Xr sshd 8
.Rs
.%A J. Galbraith
.%D March 2001
.%O work in progress material
.Re
+.Sh 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.