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SSH-KEYGEN(1)		  BSD General Commands Manual		 SSH-KEYGEN(1)

     ssh-keygen	-- authentication key generation, management and conversion

     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 [-m key_format] [-f input_keyfile]
     ssh-keygen	-e [-m key_format] [-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]
		[-J num_lines] [-j start_line] [-K checkpt] [-W	generator]
     ssh-keygen	-s ca_key -I certificate_identity [-h] [-n principals]
		[-O option] [-V	validity_interval] [-z serial_number] file ...
     ssh-keygen	-L [-f input_keyfile]
     ssh-keygen	-A

     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 DSA, ECDSA or RSA keys	for use	by SSH protocol	version	2.  The	type
     of	key to be generated is specified with the -t option.  If invoked with-
     out 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	public key authentication runs
     this once to create the authentication key	in ~/.ssh/identity,
     ~/.ssh/id_ecdsa, ~/.ssh/id_dsa or ~/.ssh/id_rsa.  Additionally, the sys-
     tem 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 se-
     ries of words, punctuation, numbers, whitespace, or any string of charac-
     ters you want.  Good passphrases are 10-30	characters long, are not sim-
     ple 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-alphanu-
     meric characters.	The passphrase can be changed later by using the -p

     There is no way to	recover	a lost passphrase.  If the passphrase is lost
     or	forgotten, a new key must be generated and the corresponding public
     key copied	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	     For each of the key types (rsa1, rsa, dsa and ecdsa) for which
	     host keys do not exist, generate the host keys with the default
	     key file path, an empty passphrase, default bits for the key
	     type, and default comment.	 This is used by /etc/rc to generate
	     new host keys.

     -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

     -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 ex-
	     actly 1024	bits as	specified by FIPS 186-2.  For ECDSA keys, the
	     -b	flag determines	the key	length by selecting from one of	three
	     elliptic curve sizes: 256,	384 or 521 bits.  Attempting to	use
	     bit lengths other than these three	values for ECDSA keys will

     -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 li-
	     brary pkcs11.  When used in combination with -s, this option in-
	     dicates that a CA key resides in a	PKCS#11	token (see the
	     CERTIFICATES section for details).

     -e	     This option will read a private or	public OpenSSH key file	and
	     print to stdout the key in	one of the formats specified by	the -m
	     option.  The default export format	is "RFC4716".  This option al-
	     lows exporting OpenSSH keys for use by other programs, including
	     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 ad-
	     dresses 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	the format specified by	the -m option and print	an OpenSSH
	     compatible	private	(or public) key	to stdout.

     -J	num_lines
	     Exit after	screening the specified	number of lines	while perform-
	     ing DH candidate screening	using the -T option.

     -j	start_line
	     Start screening at	the specified line number while	performing DH
	     candidate screening using the -T option.

     -K	checkpt
	     Write the last line processed to the file checkpt while perform-
	     ing DH candidate screening	using the -T option.  This will	be
	     used to skip lines	in the input file that have already been pro-
	     cessed if the job is restarted.  This option allows importing
	     keys from other software, including several commercial SSH	imple-
	     mentations.  The default import format is "RFC4716".

     -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.

     -m	key_format
	     Specify a key format for the -i (import) or -e (export) conver-
	     sion options.  The	supported key formats are: "RFC4716" (RFC
	     4716/SSH2 public or private key), "PKCS8" (PEM PKCS8 public key)
	     or	"PEM" (PEM public key).	 The default conversion	format is

     -N	new_passphrase
	     Provides the new passphrase.

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

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

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

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

		     Disable ssh-agent(1) forwarding (permitted	by default).

		     Disable port forwarding (permitted	by default).

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

		     Disable execution of ~/.ssh/rc by sshd(8) (permitted by

		     Disable X11 forwarding (permitted by default).

		     Allows ssh-agent(1) forwarding.

		     Allows port forwarding.

		     Allows PTY	allocation.

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

		     Allows X11	forwarding.

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

	     At	present, no options 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.

     -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

     -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

     -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 "dsa", "ecdsa" or "rsa" for
	     protocol 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 ex-
	     plicit 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 sec-
	     tion of sshd_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-

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

     -z	serial_number
	     Specifies a serial	number to be embedded in the certificate to
	     distinguish this certificate from others from the same CA.	 The
	     default serial number is zero.

     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	screened 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.

     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 a set of	options	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 ssl(8).

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

	   $ ssh-keygen	-s /path/to/ca_key -I key_id /path/to/

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

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

     The host certificate will be output to /path/to/

     It	is possible to sign using a CA key stored in a PKCS#11 token by	pro-
     viding the	token library using -D and identifying the CA key by providing
     its public	half as	an argument to -s:

	   $ ssh-keygen	-s -D -I key_id

     In	all 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-

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

     Additional	limitations on the validity and	use of user certificates may
     be	specified through certificate options.	A certificate option may dis-
     able 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 options, 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-

     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.

	     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.  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.

	     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.

	     Contains the protocol version 2 DSA, ECDSA	or 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	gener-
	     ating the key; that passphrase will be used to encrypt the	pri-
	     vate part of this file using 128-bit AES.	This file is not auto-
	     matically accessed	by ssh-keygen but it is	offered	as the default
	     file for the private key.	ssh(1) will read this file when	a lo-
	     gin attempt is made.

	     Contains the protocol version 2 DSA, ECDSA	or RSA public key for
	     authentication.  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.

	     Contains Diffie-Hellman groups used for DH-GEX.  The file format
	     is	described in moduli(5).

     ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)

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

     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.

BSD				  July 6 2012				   BSD


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