+.\" $OpenBSD: ssh-keygen.1,v 1.80 2009/10/24 00:48:34 dtucker Exp $
+.\"
.\" -*- nroff -*-
.\"
.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
.\" called by a name other than "ssh" or "Secure Shell".
.\"
.\"
-.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
-.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
-.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
+.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
+.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
+.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
-.Dd September 25, 1999
+.Dd $Mdocdate$
.Dt SSH-KEYGEN 1
.Os
.Sh NAME
.Nm ssh-keygen
-.Nd authentication key generation
+.Nd authentication key generation, management and conversion
.Sh SYNOPSIS
.Nm ssh-keygen
+.Bk -words
.Op Fl q
.Op Fl b Ar bits
-.Op Fl t Ar type
+.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
.Op Fl N Ar new_passphrase
.Op Fl f Ar keyfile
.Nm ssh-keygen
-.Fl x
+.Fl i
.Op Fl f Ar input_keyfile
.Nm ssh-keygen
-.Fl X
+.Fl e
.Op Fl f Ar input_keyfile
.Nm ssh-keygen
.Fl y
.Fl l
.Op Fl f Ar input_keyfile
.Nm ssh-keygen
-.Fl R
+.Fl B
+.Op Fl f Ar input_keyfile
+.Nm ssh-keygen
+.Fl D Ar reader
+.Nm ssh-keygen
+.Fl F Ar hostname
+.Op Fl f Ar known_hosts_file
+.Op Fl l
+.Nm ssh-keygen
+.Fl H
+.Op Fl f Ar known_hosts_file
+.Nm ssh-keygen
+.Fl R Ar hostname
+.Op Fl f Ar known_hosts_file
+.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 and manages authentication keys for
+generates, manages and converts authentication keys for
.Xr ssh 1 .
.Nm
-defaults to generating an RSA key for use by protocols 1.3 and 1.5;
-specifying 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 allows you to create a key for use by protocol 2.0.
+option.
+If invoked without any arguments,
+.Nm
+will generate an RSA key for use in SSH protocol 2 connections.
+.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
-.Pa $HOME/.ssh/identity
+.Pa ~/.ssh/identity ,
+.Pa ~/.ssh/id_dsa
or
-.Pa $HOME/.ssh/id_dsa .
+.Pa ~/.ssh/id_rsa .
Additionally, the system administrator may use this to generate host keys,
as seen in
.Pa /etc/rc .
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
+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
+characters 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 word, and provides very bad
-passphrases).
+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
.Fl p
option.
.Pp
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
+lost or forgotten, a new key must be generated and copied to the
corresponding public key to other machines.
.Pp
-For RSA, there is also a comment field in the key file that is only for
+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 initialized to
.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
+Show the bubblebabble digest of specified private or public key file.
.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.
-The default is 1024 bits.
+For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
+Generally, 2048 bits is considered sufficient.
+DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
+.It Fl C Ar comment
+Provides a new comment.
.It Fl c
Requests changing the comment in the private and public key files.
+This operation is only supported for RSA1 keys.
The program will prompt for the file containing the private keys, for
-passphrase if the key has one, and for the new comment.
-.It Fl f
+the passphrase if the key has one, and for the new comment.
+.It Fl D Ar reader
+Download the RSA public key stored in the smartcard in
+.Ar reader .
+.It Fl e
+This option will read a private or public OpenSSH key file and
+print the key in
+RFC 4716 SSH Public Key File Format
+to stdout.
+This option allows exporting keys for use by several commercial
+SSH implementations.
+.It Fl F Ar hostname
+Search for the specified
+.Ar hostname
+in a
+.Pa known_hosts
+file, listing any occurrences found.
+This option is useful to find hashed host names or addresses and may also be
+used in conjunction with the
+.Fl H
+option to print found keys in a hashed format.
+.It Fl f Ar filename
Specifies the filename of the key file.
+.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 g
+Use generic DNS format when printing fingerprint resource records using the
+.Fl r
+command.
+.It Fl H
+Hash a
+.Pa known_hosts
+file.
+This replaces all hostnames and addresses with hashed representations
+within the specified file; the original content is moved to a file with
+a .old suffix.
+These hashes may be used normally by
+.Nm ssh
+and
+.Nm sshd ,
+but they do not reveal identifying information should the file's contents
+be disclosed.
+This option will not modify existing hashed hostnames and is therefore safe
+to use on files that mix hashed and non-hashed names.
+.It Fl 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.
+.Nm
+also reads the
+RFC 4716 SSH Public Key File Format.
+This option allows importing keys from several commercial
+SSH implementations.
.It Fl l
-Show fingerprint of specified private or public key file.
+Show fingerprint of specified public key file.
+Private RSA1 keys are also supported.
+For RSA and DSA keys
+.Nm
+tries to find the matching public key file and prints its fingerprint.
+If combined with
+.Fl v ,
+an ASCII art representation of the key is supplied with the fingerprint.
+.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 p
Requests changing the passphrase of a private key file instead of
creating a new private key.
Used by
.Pa /etc/rc
when creating a new key.
+.It Fl R Ar hostname
+Removes all keys belonging to
+.Ar hostname
+from a
+.Pa known_hosts
+file.
+This option is useful to delete hashed hosts (see the
+.Fl H
+option above).
+.It Fl r Ar hostname
+Print the SSHFP fingerprint resource record named
+.Ar hostname
+for the specified public key file.
+.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 t Ar type
-Specifies the type of the key to create.
+Specifies the type of key to create.
The possible values are
.Dq rsa1
for protocol version 1 and
or
.Dq dsa
for protocol version 2.
-The default is
-.Dq rsa .
-.It Fl C Ar comment
-Provides the new comment.
-.It Fl N Ar new_passphrase
-Provides the new passphrase.
-.It Fl P Ar passphrase
-Provides the (old) passphrase.
-.It Fl R
-If RSA support is functional, immediately exits with code 0. If RSA
-support is not functional, exits with code 1. This flag will be
-removed once the RSA patent expires.
-.It Fl x
-This option will read a private
-OpenSSH DSA format file and print a SSH2-compatible public key to stdout.
-.It Fl X
-This option will read a unencrypted
-SSH2-compatible private (or public) key file and
-print an OpenSSH compatible private (or public) key to stdout.
+.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 W Ar generator
+Specify desired generator when testing candidate moduli for DH-GEX.
.It Fl y
This option will read a private
OpenSSH format file and print an OpenSSH public key to stdout.
.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
-Contains the RSA authentication identity of the user.
+.It Pa ~/.ssh/identity
+Contains the protocol version 1 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.
+used to encrypt the private part of this file using 128-bit AES.
This file is not automatically accessed by
.Nm
but it is offered as the default file for the private key.
-.Xr sshd 8
+.Xr ssh 1
will read this file when a login attempt is made.
-.It Pa $HOME/.ssh/identity.pub
-Contains the public key for authentication.
+.It Pa ~/.ssh/identity.pub
+Contains the protocol version 1 RSA public key for authentication.
The contents of this file should be added to
-.Pa $HOME/.ssh/authorized_keys
+.Pa ~/.ssh/authorized_keys
on all machines
-where you wish to log in using RSA authentication.
+where the user wishes to log in using RSA authentication.
There is no need to keep the contents of this file secret.
-.It Pa $HOME/.ssh/id_dsa
-Contains the DSA authentication identity of the user.
+.It Pa ~/.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.
+used to encrypt the private part of this file using 128-bit AES.
This file is not automatically accessed by
.Nm
but it is offered as the default file for the private key.
-.Xr sshd 8
+.Xr ssh 1
will read this file when a login attempt is made.
-.It Pa $HOME/.ssh/id_dsa.pub
-Contains the public key for authentication.
+.It Pa ~/.ssh/id_dsa.pub
+Contains the protocol version 2 DSA public key for authentication.
The contents of this file should be added to
-.Pa $HOME/.ssh/authorized_keys2
+.Pa ~/.ssh/authorized_keys
on all machines
-where you wish to log in using public key authentication.
+where the user wishes to log in using public key authentication.
There is no need to keep the contents of this file secret.
-.El
-.Sh AUTHORS
-Tatu Ylonen <ylo@cs.hut.fi>
-.Pp
-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
-.Bl -bullet
-.It
-has all components of a restrictive nature (i.e., patents, see
-.Xr crypto 3 )
-directly removed from the source code; any licensed or patented components
-are chosen from
-external libraries.
-.It
-has been updated to support ssh protocol 1.5.
-.It
-contains added support for
-.Xr kerberos 8
-authentication and ticket passing.
-.It
-supports one-time password authentication with
-.Xr skey 1 .
+.It Pa ~/.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 128-bit AES.
+This file is not automatically accessed by
+.Nm
+but it is offered as the default file for the private key.
+.Xr ssh 1
+will read this file when a login attempt is made.
+.It Pa ~/.ssh/id_rsa.pub
+Contains the protocol version 2 RSA public key for authentication.
+The contents of this file should be added to
+.Pa ~/.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.
+.It Pa /etc/moduli
+Contains Diffie-Hellman groups used for DH-GEX.
+The file format is described in
+.Xr moduli 5 .
.El
.Sh SEE ALSO
.Xr ssh 1 ,
.Xr ssh-add 1 ,
.Xr ssh-agent 1 ,
-.Xr sshd 8 ,
-.Xr crypto 3
+.Xr moduli 5 ,
+.Xr sshd 8
+.Rs
+.%R RFC 4716
+.%T "The Secure Shell (SSH) Public Key File Format"
+.%D 2006
+.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.
andersk / openssh.git / blobdiff