ssh-keygen.1 - security/openssh-library - Rivoreo Source Code Repositories

 .\"	$OpenBSD: ssh-keygen.1,v 1.88 2010/03/08 00:28:55 djm Exp $
 .\"
 .\"  -*- nroff -*-
 .\"
 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 .\"                    All rights reserved
 .\"
 .\" As far as I am concerned, the code I have written for this software
 .\" can be used freely for any purpose.  Any derived versions of this
 .\" software must be clearly marked as such, and if the derived work is
 .\" incompatible with the protocol description in the RFC file, it must be
 .\" 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.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:
 .\" 1. Redistributions of source code must retain the above copyright
 .\"    notice, this list of conditions and the following disclaimer.
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice, this list of conditions and the following disclaimer in the
 .\"    documentation and/or other materials provided with the distribution.
 .\"
 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 .\" (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 $Mdocdate: March 8 2010 $
 .Dt SSH-KEYGEN 1
 .Os
 .Sh NAME
 .Nm ssh-keygen
 .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
 .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 i
 .Op Fl f Ar input_keyfile
 .Nm ssh-keygen
 .Fl e
 .Op Fl f Ar input_keyfile
 .Nm ssh-keygen
 .Fl y
 .Op Fl f Ar input_keyfile
 .Nm ssh-keygen
 .Fl c
 .Op Fl P Ar passphrase
 .Op Fl C Ar comment
 .Op Fl f Ar keyfile
 .Nm ssh-keygen
 .Fl l
 .Op Fl f Ar input_keyfile
 .Nm ssh-keygen
 .Fl B
 .Op Fl f Ar input_keyfile
 .Nm ssh-keygen
 .Fl D Ar pkcs11
 .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 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
 .Nm ssh-keygen
 .Fl s Ar ca_key
 .Fl I Ar certificate_identity
 .Op Fl h
 .Op Fl n Ar principals
 .Op Fl O Ar constraint
 .Op Fl V Ar validity_interval
 .Ar
 .Nm ssh-keygen
 .Fl L
 .Op Fl f Ar input_keyfile
 .Ek
 .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
 .Fl t
 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 ~/.ssh/identity ,
 .Pa ~/.ssh/id_dsa
 or
 .Pa ~/.ssh/id_rsa .
 Additionally, the system administrator may use this to generate host keys,
 as seen in
 .Pa /etc/rc .
 .Pp
 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
 .Dq .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
 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 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, a new key must be generated and copied to the
 corresponding public key to other machines.
 .Pp
 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
 .Dq user@host
 when the key is created, but can be changed using the
 .Fl c
 option.
 .Pp
 After a key is generated, instructions below detail where the keys
 should be placed to be activated.
 .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.
 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
 the passphrase if the key has one, and for the new comment.
 .It Fl D Ar pkcs11
 Download the RSA public keys provided by the PKCS#11 shared library
 .Ar pkcs11 .
 .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 h
 When signing a key, create a host certificate instead of a user
 certificate.
 Please see the
 .Sx CERTIFICATES
 section for details.
 .It Fl I Ar certificate_identity
 Specify the key identity when signing a public key.
 Please see the
 .Sx CERTIFICATES
 section for details.
 .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
 Prints the contents of a certificate.
 .It Fl l
 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 n Ar principals
 Specify one or more principals (user or host names) to be included in
 a certificate when signing a key.
 Multiple principals may be specified, separated by commas.
 Please see the
 .Sx CERTIFICATES
 section for details.
 .It Fl O Ar constraint
 Specify a certificate constraint when signing a key.
 This option may be specified multiple times.
 Please see the
 .Sx CERTIFICATES
 section for details.
 The constraints that are valid for user certificates are:
 .Bl -tag -width Ds
 .It Ic no-x11-forwarding
 Disable X11 forwarding (permitted by default).
 .It Ic no-agent-forwarding
 Disable
 .Xr ssh-agent 1
 forwarding (permitted by default).
 .It Ic no-port-forwarding
 Disable port forwarding (permitted by default).
 .It Ic no-pty
 Disable PTY allocation (permitted by default).
 .It Ic no-user-rc
 Disable execution of
 .Pa ~/.ssh/rc
 by
 .Xr sshd 8
 (permitted by default).
 .It Ic clear
 Clear all enabled permissions.
 This is useful for clearing the default set of permissions so permissions may
 be added individually.
 .It Ic permit-x11-forwarding
 Allows X11 forwarding.
 .It Ic permit-agent-forwarding
 Allows
 .Xr ssh-agent 1
 forwarding.
 .It Ic permit-port-forwarding
 Allows port forwarding.
 .It Ic permit-pty
 Allows PTY allocation.
 .It Ic permit-user-rc
 Allows execution of
 .Pa ~/.ssh/rc
 by
 .Xr sshd 8 .
 .It Ic force-command=command
 Forces the execution of
 .Ar command
 instead of any shell or command specified by the user when
 the certificate is used for authentication.
 .It Ic source-address=address_list
 Restrict the source addresses from which the certificate is considered valid
 from.
 The
 .Ar address_list
 is a comma-separated list of one or more address/netmask pairs in CIDR
 format.
 .El
 .Pp
 At present, no constraints are valid for host keys.
 .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.
 The program will prompt for the file
 containing the private key, for the old passphrase, and twice for the
 new passphrase.
 .It Fl q
 Silence
 .Nm ssh-keygen .
 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 s Ar ca_key
 Certify (sign) a public key using the specified CA key.
 Please see the
 .Sx CERTIFICATES
 section for details.
 .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 key to create.
 The possible values are
 .Dq rsa1
 for protocol version 1 and
 .Dq rsa
 or
 .Dq dsa
 for protocol version 2.
 .It Fl V Ar validity_interval
 Specify a validity interval when signing a certificate.
 A validity interval may consist of a single time, indicating that the
 certificate is valid beginning now and expiring at that time, or may consist
 of two times separated by a colon to indicate an explicit time interval.
 The start time may be specified as a date in YYYYMMDD format, a time
 in YYYYMMDDHHMMSS format or a relative time (to the current time) consisting
 of a minus sign followed by a relative time in the format described in the
 .Sx TIME FORMATS
 section of
 .Xr ssh_config 5 .
 The end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMMSS time or
 a relative time starting with a plus character.
 .Pp
 For example:
 .Dq +52w1d
 (valid from now to 52 weeks and one day from now),
 .Dq -4w:+4w
 (valid from four weeks ago to four weeks from now),
 .Dq 20100101123000:20110101123000
 (valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
 .Dq -1d:20110101
 (valid from yesterday to midnight, January 1st, 2011).
 .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 CERTIFICATES
 .Nm
 supports signing of keys to produce certificates that may be used for
 user or host authentication.
 Certificates consist of a public key, some identity information, zero or
 more principal (user or host) names and an optional set of constraints that
 are signed by a Certification Authority (CA) key.
 Clients or servers may then trust only the CA key and verify its signature
 on a certificate rather than trusting many user/host keys.
 Note that OpenSSH certificates are a different, and much simpler, format to
 the X.509 certificates used in
 .Xr ssl 8 .
 .Pp
 .Nm
 supports two types of certificates: user and host.
 User certificates authenticate users to servers, whereas host certificates
 authenticate server hosts to users.
 To generate a user certificate:
 .Pp
 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
 .Pp
 The resultant certificate will be placed in
 .Pa /path/to/user_key_cert.pub .
 A host certificate requires the
 .Fl h
 option:
 .Pp
 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
 .Pp
 The host certificate will be output to
 .Pa /path/to/host_key_cert.pub .
 In both cases,
 .Ar key_id
 is a "key identifier" that is logged by the server when the certificate
 is used for authentication.
 .Pp
 Certificates may be limited to be valid for a set of principal (user/host)
 names.
 By default, generated certificates are valid for all users or hosts.
 To generate a certificate for a specified set of principals:
 .Pp
 .Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
 .Dl $ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub
 .Pp
 Additional limitations on the validity and use of user certificates may
 be specified through certificate constraints.
 A constrained certificate may disable features of the SSH session, may be
 valid only when presented from particular source addresses or may
 force the use of a specific command.
 For a list of valid certificate constraints, see the documentation for the
 .Fl O
 option above.
 .Pp
 Finally, certificates may be defined with a validity lifetime.
 The
 .Fl V
 option allows specification of certificate start and end times.
 A certificate that is presented at a time outside this range will not be
 considered valid.
 By default, certificates have a maximum validity interval.
 .Pp
 For certificates to be used for user or host authentication, the CA
 public key must be trusted by
 .Xr sshd 8
 or
 .Xr ssh 1 .
 Please refer to those manual pages for details.
 .Sh FILES
 .Bl -tag -width Ds
 .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 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/identity.pub
 Contains the protocol version 1 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 RSA authentication.
 There is no need to keep the contents of this file secret.
 .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 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_dsa.pub
 Contains the protocol version 2 DSA 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 ~/.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 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.
	.\" $OpenBSD: ssh-keygen.1,v 1.88 2010/03/08 00:28:55 djm Exp $
	.\"
	.\" -- nroff --
	.\"
	.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
	.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
	.\" All rights reserved
	.\"
	.\" As far as I am concerned, the code I have written for this software
	.\" can be used freely for any purpose. Any derived versions of this
	.\" software must be clearly marked as such, and if the derived work is
	.\" incompatible with the protocol description in the RFC file, it must be
	.\" 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.
	.\"
	.\" Redistribution and use in source and binary forms, with or without
	.\" modification, are permitted provided that the following conditions
	.\" are met:
	.\" 1. Redistributions of source code must retain the above copyright
	.\" notice, this list of conditions and the following disclaimer.
	.\" 2. Redistributions in binary form must reproduce the above copyright
	.\" notice, this list of conditions and the following disclaimer in the
	.\" documentation and/or other materials provided with the distribution.
	.\"
	.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
	.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
	.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
	.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	.\" (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 $Mdocdate: March 8 2010 $
	.Dt SSH-KEYGEN 1
	.Os
	.Sh NAME
	.Nm ssh-keygen
	.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
	.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 i
	.Op Fl f Ar input_keyfile
	.Nm ssh-keygen
	.Fl e
	.Op Fl f Ar input_keyfile
	.Nm ssh-keygen
	.Fl y
	.Op Fl f Ar input_keyfile
	.Nm ssh-keygen
	.Fl c
	.Op Fl P Ar passphrase
	.Op Fl C Ar comment
	.Op Fl f Ar keyfile
	.Nm ssh-keygen
	.Fl l
	.Op Fl f Ar input_keyfile
	.Nm ssh-keygen
	.Fl B
	.Op Fl f Ar input_keyfile
	.Nm ssh-keygen
	.Fl D Ar pkcs11
	.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 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
	.Nm ssh-keygen
	.Fl s Ar ca_key
	.Fl I Ar certificate_identity
	.Op Fl h
	.Op Fl n Ar principals
	.Op Fl O Ar constraint
	.Op Fl V Ar validity_interval
	.Ar
	.Nm ssh-keygen
	.Fl L
	.Op Fl f Ar input_keyfile
	.Ek
	.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
	.Fl t
	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 ~/.ssh/identity ,
	.Pa ~/.ssh/id_dsa
	or
	.Pa ~/.ssh/id_rsa .
	Additionally, the system administrator may use this to generate host keys,
	as seen in
	.Pa /etc/rc .
	.Pp
	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
	.Dq .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
	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 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, a new key must be generated and copied to the
	corresponding public key to other machines.
	.Pp
	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
	.Dq user@host
	when the key is created, but can be changed using the
	.Fl c
	option.
	.Pp
	After a key is generated, instructions below detail where the keys
	should be placed to be activated.
	.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.
	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
	the passphrase if the key has one, and for the new comment.
	.It Fl D Ar pkcs11
	Download the RSA public keys provided by the PKCS#11 shared library
	.Ar pkcs11 .
	.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 h
	When signing a key, create a host certificate instead of a user
	certificate.
	Please see the
	.Sx CERTIFICATES
	section for details.
	.It Fl I Ar certificate_identity
	Specify the key identity when signing a public key.
	Please see the
	.Sx CERTIFICATES
	section for details.
	.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
	Prints the contents of a certificate.
	.It Fl l
	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 n Ar principals
	Specify one or more principals (user or host names) to be included in
	a certificate when signing a key.
	Multiple principals may be specified, separated by commas.
	Please see the
	.Sx CERTIFICATES
	section for details.
	.It Fl O Ar constraint
	Specify a certificate constraint when signing a key.
	This option may be specified multiple times.
	Please see the
	.Sx CERTIFICATES
	section for details.
	The constraints that are valid for user certificates are:
	.Bl -tag -width Ds
	.It Ic no-x11-forwarding
	Disable X11 forwarding (permitted by default).
	.It Ic no-agent-forwarding
	Disable
	.Xr ssh-agent 1
	forwarding (permitted by default).
	.It Ic no-port-forwarding
	Disable port forwarding (permitted by default).
	.It Ic no-pty
	Disable PTY allocation (permitted by default).
	.It Ic no-user-rc
	Disable execution of
	.Pa ~/.ssh/rc
	by
	.Xr sshd 8
	(permitted by default).
	.It Ic clear
	Clear all enabled permissions.
	This is useful for clearing the default set of permissions so permissions may
	be added individually.
	.It Ic permit-x11-forwarding
	Allows X11 forwarding.
	.It Ic permit-agent-forwarding
	Allows
	.Xr ssh-agent 1
	forwarding.
	.It Ic permit-port-forwarding
	Allows port forwarding.
	.It Ic permit-pty
	Allows PTY allocation.
	.It Ic permit-user-rc
	Allows execution of
	.Pa ~/.ssh/rc
	by
	.Xr sshd 8 .
	.It Ic force-command=command
	Forces the execution of
	.Ar command
	instead of any shell or command specified by the user when
	the certificate is used for authentication.
	.It Ic source-address=address_list
	Restrict the source addresses from which the certificate is considered valid
	from.
	The
	.Ar address_list
	is a comma-separated list of one or more address/netmask pairs in CIDR
	format.
	.El
	.Pp
	At present, no constraints are valid for host keys.
	.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.
	The program will prompt for the file
	containing the private key, for the old passphrase, and twice for the
	new passphrase.
	.It Fl q
	Silence
	.Nm ssh-keygen .
	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 s Ar ca_key
	Certify (sign) a public key using the specified CA key.
	Please see the
	.Sx CERTIFICATES
	section for details.
	.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 key to create.
	The possible values are
	.Dq rsa1
	for protocol version 1 and
	.Dq rsa
	or
	.Dq dsa
	for protocol version 2.
	.It Fl V Ar validity_interval
	Specify a validity interval when signing a certificate.
	A validity interval may consist of a single time, indicating that the
	certificate is valid beginning now and expiring at that time, or may consist
	of two times separated by a colon to indicate an explicit time interval.
	The start time may be specified as a date in YYYYMMDD format, a time
	in YYYYMMDDHHMMSS format or a relative time (to the current time) consisting
	of a minus sign followed by a relative time in the format described in the
	.Sx TIME FORMATS
	section of
	.Xr ssh_config 5 .
	The end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMMSS time or
	a relative time starting with a plus character.
	.Pp
	For example:
	.Dq +52w1d
	(valid from now to 52 weeks and one day from now),
	.Dq -4w:+4w
	(valid from four weeks ago to four weeks from now),
	.Dq 20100101123000:20110101123000
	(valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
	.Dq -1d:20110101
	(valid from yesterday to midnight, January 1st, 2011).
	.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 CERTIFICATES
	.Nm
	supports signing of keys to produce certificates that may be used for
	user or host authentication.
	Certificates consist of a public key, some identity information, zero or
	more principal (user or host) names and an optional set of constraints that
	are signed by a Certification Authority (CA) key.
	Clients or servers may then trust only the CA key and verify its signature
	on a certificate rather than trusting many user/host keys.
	Note that OpenSSH certificates are a different, and much simpler, format to
	the X.509 certificates used in
	.Xr ssl 8 .
	.Pp
	.Nm
	supports two types of certificates: user and host.
	User certificates authenticate users to servers, whereas host certificates
	authenticate server hosts to users.
	To generate a user certificate:
	.Pp
	.Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
	.Pp
	The resultant certificate will be placed in
	.Pa /path/to/user_key_cert.pub .
	A host certificate requires the
	.Fl h
	option:
	.Pp
	.Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
	.Pp
	The host certificate will be output to
	.Pa /path/to/host_key_cert.pub .
	In both cases,
	.Ar key_id
	is a "key identifier" that is logged by the server when the certificate
	is used for authentication.
	.Pp
	Certificates may be limited to be valid for a set of principal (user/host)
	names.
	By default, generated certificates are valid for all users or hosts.
	To generate a certificate for a specified set of principals:
	.Pp
	.Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
	.Dl $ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub
	.Pp
	Additional limitations on the validity and use of user certificates may
	be specified through certificate constraints.
	A constrained certificate may disable features of the SSH session, may be
	valid only when presented from particular source addresses or may
	force the use of a specific command.
	For a list of valid certificate constraints, see the documentation for the
	.Fl O
	option above.
	.Pp
	Finally, certificates may be defined with a validity lifetime.
	The
	.Fl V
	option allows specification of certificate start and end times.
	A certificate that is presented at a time outside this range will not be
	considered valid.
	By default, certificates have a maximum validity interval.
	.Pp
	For certificates to be used for user or host authentication, the CA
	public key must be trusted by
	.Xr sshd 8
	or
	.Xr ssh 1 .
	Please refer to those manual pages for details.
	.Sh FILES
	.Bl -tag -width Ds
	.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 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/identity.pub
	Contains the protocol version 1 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 RSA authentication.
	There is no need to keep the contents of this file secret.
	.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 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_dsa.pub
	Contains the protocol version 2 DSA 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 ~/.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 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.