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SSH-KEYGEN(1)		FreeBSD	General	Commands 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 pkcs11
     ssh-keygen	-F hostname [-f	known_hosts_file] [-l]
     ssh-keygen	-H [-f known_hosts_file]
     ssh-keygen	-R hostname [-f	known_hosts_file]
     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]
     ssh-keygen	-s ca_key -I certificate_identity [-h] [-n principals]
		[-O constraint]	[-V validity_interval] file ...
     ssh-keygen	-L [-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.  If invoked without any
     arguments,	ssh-keygen will	generate an RSA	key for	use in SSH protocol 2
     connections.

     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 ~/.ssh/identity,
     ~/.ssh/id_dsa or ~/.ssh/id_rsa.  Additionally, the	system administrator
     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.

     After a key is generated, instructions below detail where the keys	should
     be	placed to be activated.

     The options are as	follows:

     -a	trials
	     Specifies the number of primality tests to	perform	when screening
	     DH-GEX candidates using the -T command.

     -B	     Show the bubblebabble digest of specified private or public key
	     file.

     -b	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.	 Gen-
	     erally, 2048 bits is considered sufficient.  DSA keys must	be
	     exactly 1024 bits as specified by FIPS 186-2.

     -C	comment
	     Provides a	new comment.

     -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.

     -D	pkcs11
	     Download the RSA public keys provided by the PKCS#11 shared
	     library pkcs11.

     -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.

     -F	hostname
	     Search for	the specified hostname in a 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
	     -H	option to print	found keys in a	hashed format.

     -f	filename
	     Specifies the filename of the key file.

     -G	output_file
	     Generate candidate	primes for DH-GEX.  These primes must be
	     screened for safety (using	the -T option) before use.

     -g	     Use generic DNS format when printing fingerprint resource records
	     using the -r command.

     -H	     Hash a 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 ssh and 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.

     -h	     When signing a key, create	a host certificate instead of a	user
	     certificate.  Please see the CERTIFICATES section for details.

     -I	certificate_identity
	     Specify the key identity when signing a public key.  Please see
	     the CERTIFICATES section for details.

     -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 RFC 4716
	     SSH Public	Key File Format.  This option allows importing keys
	     from several commercial SSH implementations.

     -L	     Prints the	contents of a certificate.

     -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.  If
	     combined with -v, an ASCII	art representation of the key is sup-
	     plied with	the fingerprint.

     -M	memory
	     Specify the amount	of memory to use (in megabytes)	when generat-
	     ing candidate moduli for DH-GEX.

     -N	new_passphrase
	     Provides the new passphrase.

     -n	principals
	     Specify one or more principals (user or host names) to be
	     included in a certificate when signing a key.  Multiple princi-
	     pals may be specified, separated by commas.  Please see the
	     CERTIFICATES section for details.

     -O	constraint
	     Specify a certificate constraint when signing a key.  This	option
	     may be specified multiple times.  Please see the CERTIFICATES
	     section for details.  The constraints that	are valid for user
	     certificates are:

	     no-x11-forwarding
		     Disable X11 forwarding (permitted by default).

	     no-agent-forwarding
		     Disable ssh-agent(1) forwarding (permitted	by default).

	     no-port-forwarding
		     Disable port forwarding (permitted	by default).

	     no-pty  Disable PTY allocation (permitted by default).

	     no-user-rc
		     Disable execution of ~/.ssh/rc by sshd(8) (permitted by
		     default).

	     clear   Clear all enabled permissions.  This is useful for	clear-
		     ing the default set of permissions	so permissions may be
		     added individually.

	     permit-x11-forwarding
		     Allows X11	forwarding.

	     permit-agent-forwarding
		     Allows ssh-agent(1) forwarding.

	     permit-port-forwarding
		     Allows port forwarding.

	     permit-pty
		     Allows PTY	allocation.

	     permit-user-rc
		     Allows execution of ~/.ssh/rc by sshd(8).

	     force-command=command
		     Forces the	execution of command instead of	any shell or
		     command specified by the user when	the certificate	is
		     used for authentication.

	     source-address=address_list
		     Restrict the source addresses from	which the certificate
		     is	considered valid from.	The address_list is a comma-
		     separated list of one or more address/netmask pairs in
		     CIDR format.

	     At	present, no constraints	are valid for host keys.

     -P	passphrase
	     Provides the (old)	passphrase.

     -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.

     -R	hostname
	     Removes all keys belonging	to hostname from a known_hosts file.
	     This option is useful to delete hashed hosts (see the -H option
	     above).

     -r	hostname
	     Print the SSHFP fingerprint resource record named hostname	for
	     the specified public key file.

     -S	start
	     Specify start point (in hex) when generating candidate moduli for
	     DH-GEX.

     -s	ca_key
	     Certify (sign) a public key using the specified CA	key.  Please
	     see the CERTIFICATES section for details.

     -T	output_file
	     Test DH group exchange candidate primes (generated	using the -G
	     option) for safety.

     -t	type
	     Specifies the type	of key to create.  The possible	values are
	     ``rsa1'' for protocol version 1 and ``rsa'' or ``dsa'' for	proto-
	     col version 2.

     -V	validity_interval
	     Specify a validity	interval when signing a	certificate.  A	valid-
	     ity 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	TIME
	     FORMATS section of	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.

	     For example: ``+52w1d'' (valid from now to	52 weeks and one day
	     from now),	``-4w:+4w'' (valid from	four weeks ago to four weeks
	     from now),	``20100101123000:20110101123000'' (valid from 12:30
	     PM, January 1st, 2010 to 12:30 PM,	January	1st, 2011),
	     ``-1d:20110101'' (valid from yesterday to midnight, January 1st,
	     2011).

     -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.

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

     -y	     This option will read a private OpenSSH format file and print an
	     OpenSSH public key	to stdout.

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
     a connection share	common moduli.

CERTIFICATES
     ssh-keygen	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 Certifica-
     tion 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 ssl(8).

     ssh-keygen	supports two types of certificates: user and host.  User cer-
     tificates authenticate users to servers, whereas host certificates
     authenticate server hosts to users.  To generate a	user certificate:

	   $ ssh-keygen	-s /path/to/ca_key -I key_id /path/to/user_key.pub

     The resultant certificate will be placed in /path/to/user_key_cert.pub.
     A host certificate	requires the -h	option:

	   $ ssh-keygen	-s /path/to/ca_key -I key_id -h	/path/to/host_key.pub

     The host certificate will be output to /path/to/host_key_cert.pub.	 In
     both cases, key_id	is a "key identifier" that is logged by	the server
     when the certificate is used for authentication.

     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 princi-
     pals:

	   $ ssh-keygen	-s ca_key -I key_id -n user1,user2 user_key.pub
	   $ ssh-keygen	-s ca_key -I key_id -h -n host.domain user_key.pub

     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 com-
     mand.  For	a list of valid	certificate constraints, see the documentation
     for the -O	option above.

     Finally, certificates may be defined with a validity lifetime.  The -V
     option allows specification of certificate	start and end times.  A	cer-
     tificate that is presented	at a time outside this range will not be con-
     sidered valid.  By	default, certificates have a maximum validity inter-
     val.

     For certificates to be used for user or host authentication, the CA pub-
     lic key must be trusted by	sshd(8)	or ssh(1).  Please refer to those man-
     ual pages for details.

FILES
     ~/.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 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.

     ~/.ssh/identity.pub
	     Contains the protocol version 1 RSA public	key for	authentica-
	     tion.  The	contents of this file should be	added to
	     ~/.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.

     ~/.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 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.

     ~/.ssh/id_dsa.pub
	     Contains the protocol version 2 DSA public	key for	authentica-
	     tion.  The	contents of this file should be	added to
	     ~/.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.

     ~/.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 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.

     ~/.ssh/id_rsa.pub
	     Contains the protocol version 2 RSA public	key for	authentica-
	     tion.  The	contents of this file should be	added to
	     ~/.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)

     The Secure	Shell (SSH) Public Key File Format, RFC	4716, 2006.

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.

FreeBSD	9.2			 March 8, 2010			   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | MODULI GENERATION | CERTIFICATES | FILES | SEE ALSO | AUTHORS

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