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

     ssh-keygen	-- OpenSSH authentication key utility

     ssh-keygen	[-q] [-a rounds] [-b bits] [-C comment]	[-f output_keyfile]
		[-m format] [-N	new_passphrase]	[-O option]
		[-t dsa	| ecdsa	| ecdsa-sk | ed25519 | ed25519-sk | rsa]
		[-w provider] [-Z cipher]
     ssh-keygen	-p [-a rounds] [-f keyfile] [-m	format]	[-N new_passphrase]
		[-P old_passphrase] [-Z	cipher]
     ssh-keygen	-i [-f input_keyfile] [-m key_format]
     ssh-keygen	-e [-f input_keyfile] [-m key_format]
     ssh-keygen	-y [-f input_keyfile]
     ssh-keygen	-c [-a rounds] [-C comment] [-f	keyfile] [-P passphrase]
     ssh-keygen	-l [-v]	[-E fingerprint_hash] [-f input_keyfile]
     ssh-keygen	-B [-f input_keyfile]
     ssh-keygen	-D pkcs11
     ssh-keygen	-F hostname [-lv] [-f known_hosts_file]
     ssh-keygen	-H [-f known_hosts_file]
     ssh-keygen	-K [-a rounds] [-w provider]
     ssh-keygen	-R hostname [-f	known_hosts_file]
     ssh-keygen	-r hostname [-g] [-f input_keyfile]
     ssh-keygen	-M generate [-O	option]	output_file
     ssh-keygen	-M screen [-f input_file] [-O option] output_file
     ssh-keygen	-I certificate_identity	-s ca_key [-hU]	[-D pkcs11_provider]
		[-n principals]	[-O option] [-V	validity_interval]
		[-z serial_number] file	...
     ssh-keygen	-L [-f input_keyfile]
     ssh-keygen	-A [-a rounds] [-f prefix_path]
     ssh-keygen	-k -f krl_file [-u] [-s	ca_public] [-z version_number]
		file ...
     ssh-keygen	-Q [-l]	-f krl_file file ...
     ssh-keygen	-Y find-principals [-O option] -s signature_file -f
     ssh-keygen	-Y match-principals -I signer_identity -f allowed_signers_file
     ssh-keygen	-Y check-novalidate [-O	option]	-n namespace -s	signature_file
     ssh-keygen	-Y sign	[-O option] -f key_file	-n namespace file ...
     ssh-keygen	-Y verify [-O option] -f allowed_signers_file -I
		signer_identity	-n namespace -s	signature_file
		[-r revocation_file]

     ssh-keygen	generates, manages and converts	authentication keys for
     ssh(1).  ssh-keygen can create keys for use by SSH	protocol version 2.

     The type of key to	be generated is	specified with the -t option.  If in-
     voked without any arguments, ssh-keygen will generate an RSA key.

     ssh-keygen	is also	used to	generate groups	for use	in Diffie-Hellman
     group exchange (DH-GEX).  See the MODULI GENERATION section for details.

     Finally, ssh-keygen can be	used to	generate and update Key	Revocation
     Lists, and	to test	whether	given keys have	been revoked by	one.  See the
     KEY REVOCATION LISTS section for details.

     Normally each user	wishing	to use SSH with	public key authentication runs
     this once to create the authentication key	in ~/.ssh/id_dsa,
     ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
     ~/.ssh/id_ed25519_sk or ~/.ssh/id_rsa.  Additionally, the system adminis-
     trator 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.

     ssh-keygen	will by	default	write keys in an OpenSSH-specific format.
     This format is preferred as it offers better protection for keys at rest
     as	well as	allowing storage of key	comments within	the private key	file
     itself.  The key comment may be useful to help identify the key.  The
     comment is	initialized to "user@host" when	the key	is created, but	can be
     changed using the -c option.

     It	is still possible for ssh-keygen to write the previously-used PEM for-
     mat private keys using the	-m flag.  This may be used when	generating new
     keys, and existing	new-format keys	may be converted using this option in
     conjunction with the -p (change passphrase) flag.

     After a key is generated, ssh-keygen will ask where the keys should be
     placed to be activated.

     The options are as	follows:

     -A	     Generate host keys	of all default key types (rsa, ecdsa, and
	     ed25519) if they do not already exist.  The host keys are gener-
	     ated with the default key file path, an empty passphrase, default
	     bits for the key type, and	default	comment.  If -f	has also been
	     specified,	its argument is	used as	a prefix to the	default	path
	     for the resulting host key	files.	This is	used by	/etc/rc	to
	     generate new host keys.

     -a	rounds
	     When saving a private key,	this option specifies the number of
	     KDF (key derivation function, currently bcrypt_pbkdf(3)) rounds
	     used.  Higher numbers result in slower passphrase verification
	     and increased resistance to brute-force password cracking (should
	     the keys be stolen).  The default is 16 rounds.

     -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 1024 bits and the default is 3072 bits.  Gen-
	     erally, 3072 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
	     fail.  ECDSA-SK, Ed25519 and Ed25519-SK keys have a fixed length
	     and the -b	flag will be ignored.

     -C	comment
	     Provides a	new comment.

     -c	     Requests changing the comment in the private and public key
	     files.  The program will prompt for the file containing the pri-
	     vate keys,	for the	passphrase if the key has one, and for the new

     -D	pkcs11
	     Download the public keys provided by the PKCS#11 shared library
	     pkcs11.  When used	in combination with -s,	this option indicates
	     that a CA key resides in a	PKCS#11	token (see the CERTIFICATES
	     section for details).

     -E	fingerprint_hash
	     Specifies the hash	algorithm used when displaying key finger-
	     prints.  Valid options are: "md5" and "sha256".  The default is

     -e	     This option will read a private or	public OpenSSH key file	and
	     print to stdout a public key in one of the	formats	specified by
	     the -m option.  The default export	format is "RFC4716".  This op-
	     tion allows exporting OpenSSH keys	for use	by other programs, in-
	     cluding several commercial	SSH implementations.

     -F	hostname | [hostname]:port
	     Search for	the specified hostname (with optional port number) 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	     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.  See the CERTIFICATES	section	for details.

     -I	certificate_identity
	     Specify the key identity when signing a public key.  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.  This option	allows
	     importing keys from other software, including several commercial
	     SSH implementations.  The default import format is	"RFC4716".

     -K	     Download resident keys from a FIDO	authenticator.	Public and
	     private key files will be written to the current directory	for
	     each downloaded key.  If multiple FIDO authenticators are at-
	     tached, keys will be downloaded from the first touched authenti-
	     cator.  See the FIDO AUTHENTICATOR	section	for more information.

     -k	     Generate a	KRL file.  In this mode, ssh-keygen will generate a
	     KRL file at the location specified	via the	-f flag	that revokes
	     every key or certificate presented	on the command line.
	     Keys/certificates to be revoked may be specified by public	key
	     file or using the format described	in the KEY REVOCATION LISTS

     -L	     Prints the	contents of one	or more	certificates.

     -l	     Show fingerprint of specified public key file.  For RSA and DSA
	     keys ssh-keygen tries to find the matching	public key file	and
	     prints its	fingerprint.  If combined with -v, a visual ASCII art
	     representation of the key is supplied with	the fingerprint.

     -M	generate
	     Generate candidate	Diffie-Hellman Group Exchange (DH-GEX) parame-
	     ters for eventual use by the `diffie-hellman-group-exchange-*'
	     key exchange methods.  The	numbers	generated by this operation
	     must be further screened before use.  See the MODULI GENERATION
	     section for more information.

     -M	screen
	     Screen candidate parameters for Diffie-Hellman Group Exchange.
	     This will accept a	list of	candidate numbers and test that	they
	     are safe (Sophie Germain) primes with acceptable group genera-
	     tors.  The	results	of this	operation may be added to the
	     /etc/moduli file.	See the	MODULI GENERATION section for more in-

     -m	key_format
	     Specify a key format for key generation, the -i (import), -e (ex-
	     port) conversion options, and the -p change passphrase operation.
	     The latter	may be used to convert between OpenSSH private key and
	     PEM private key formats.  The supported key formats are:
	     "RFC4716" (RFC 4716/SSH2 public or	private	key), "PKCS8" (PKCS8
	     public or private key) or "PEM" (PEM public key).	By default
	     OpenSSH will write	newly-generated	private	keys in	its own	for-
	     mat, but when converting public keys for export the default for-
	     mat is "RFC4716".	Setting	a format of "PEM" when generating or
	     updating a	supported private key type will	cause the key to be
	     stored in the legacy PEM private key format.

     -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.  See the CERTIFICATES sec-
	     tion for details.

     -O	option
	     Specify a key/value option.  These	are specific to	the operation
	     that ssh-keygen has been requested	to perform.

	     When signing certificates,	one of the options listed in the
	     CERTIFICATES section may be specified here.

	     When performing moduli generation or screening, one of the	op-
	     tions listed in the MODULI	GENERATION section may be specified.

	     When generating FIDO authenticator-backed keys, the options
	     listed in the FIDO	AUTHENTICATOR section may be specified.

	     When performing signature-related options using the -Y flag, the
	     following options are accepted:

		     Selects the hash algorithm	to use for hashing the message
		     to	be signed.  Valid algorithms are "sha256" and
		     "sha512." The default is "sha512."

		     Print the full public key to standard output after	signa-
		     ture verification.

		     Specifies a time to use when validating signatures	in-
		     stead of the current time.	 The time may be specified as
		     a date or time in the YYYYMMDD[Z] or in YYYYMMD-
		     DHHMM[SS][Z] formats.  Dates and times will be inter-
		     preted in the current system time zone unless suffixed
		     with a Z character, which causes them to be interpreted
		     in	the UTC	time zone.

	     When generating SSHFP DNS records from public keys	using the -r
	     flag, the following options are accepted:

		     Selects a hash algorithm to use when printing SSHFP
		     records using the -D flag.	 Valid algorithms are "sha1"
		     and "sha256".  The	default	is to print both.

	     The -O option may be specified multiple times.

     -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	     Test whether keys have been revoked in a KRL.  If the -l option
	     is	also specified then the	contents of the	KRL will be printed.

     -q	     Silence ssh-keygen.

     -R	hostname | [hostname]:port
	     Removes all keys belonging	to the specified hostname (with	op-
	     tional port number) from a	known_hosts file.  This	option is use-
	     ful 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	ca_key
	     Certify (sign) a public key using the specified CA	key.  See the
	     CERTIFICATES section for details.

	     When generating a KRL, -s specifies a path	to a CA	public key
	     file used to revoke certificates directly by key ID or serial
	     number.  See the KEY REVOCATION LISTS section for details.

     -t	dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk |	rsa
	     Specifies the type	of key to create.  The possible	values are
	     "dsa", "ecdsa", "ecdsa-sk", "ed25519", "ed25519-sk", or "rsa".

	     This flag may also	be used	to specify the desired signature type
	     when signing certificates using an	RSA CA key.  The available RSA
	     signature variants	are "ssh-rsa" (SHA1 signatures,	not recom-
	     mended), "rsa-sha2-256", and "rsa-sha2-512" (the default).

     -U	     When used in combination with -s or -Y sign, this option indi-
	     cates that	a CA key resides in a ssh-agent(1).  See the
	     CERTIFICATES section for more information.

     -u	     Update a KRL.  When specified with	-k, keys listed	via the	com-
	     mand line are added to the	existing KRL rather than a new KRL be-
	     ing created.

     -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:
	     o	 The string "always" to	indicate the certificate has no	speci-
		 fied start time.
	     o	 A date	or time	in the system time zone	formatted as YYYYMMDD
	     o	 A date	or time	in the UTC time	zone as	YYYYMMDDZ or YYYYMMD-
	     o	 A relative time before	the current system time	consisting of
		 a minus sign followed by an interval in the format described
		 in the	TIME FORMATS section of	sshd_config(5).
	     o	 A raw seconds since epoch (Jan	1 1970 00:00:00	UTC) as	a
		 hexadecimal number beginning with "0x".

	     The end time may be specified similarly to	the start time:
	     o	 The string "forever" to indicate the certificate has no spec-
		 ified end time.
	     o	 A date	or time	in the system time zone	formatted as YYYYMMDD
	     o	 A date	or time	in the UTC time	zone as	YYYYMMDDZ or YYYYMMD-
	     o	 A relative time after the current system time consisting of a
		 plus sign followed by an interval in the format described in
		 the TIME FORMATS section of sshd_config(5).
	     o	 A raw seconds since epoch (Jan	1 1970 00:00:00	UTC) as	a
		 hexadecimal number beginning with "0x".

	     For example:

	     +52w1d  Valid from	now to 52 weeks	and one	day from now.

		     Valid from	four weeks ago to four weeks from now.

		     Valid from	12:30 PM, January 1st, 2010 to 12:30 PM, Janu-
		     ary 1st, 2011.

		     Similar, but interpreted in the UTC time zone rather than
		     the system	time zone.

		     Valid from	yesterday to midnight, January 1st, 2011.

		     Valid from	roughly	early 1970 to May 2033.

		     Valid from	one minute ago and never expiring.

     -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	provider
	     Specifies a path to a library that	will be	used when creating
	     FIDO authenticator-hosted keys, overriding	the default of using
	     the internal USB HID support.

     -Y	find-principals
	     Find the principal(s) associated with the public key of a signa-
	     ture, provided using the -s flag in an authorized signers file
	     provided using the	-f flag.  The format of	the allowed signers
	     file is documented	in the ALLOWED SIGNERS section below.  If one
	     or	more matching principals are found, they are returned on stan-
	     dard output.

     -Y	match-principals
	     Find principal matching the principal name	provided using the -I
	     flag in the authorized signers file specified using the -f	flag.
	     If	one or more matching principals	are found, they	are returned
	     on	standard output.

     -Y	check-novalidate
	     Checks that a signature generated using ssh-keygen	-Y sign	has a
	     valid structure.  This does not validate if a signature comes
	     from an authorized	signer.	 When testing a	signature, ssh-keygen
	     accepts a message on standard input and a signature namespace us-
	     ing -n.  A	file containing	the corresponding signature must also
	     be	supplied using the -s flag.  Successful	testing	of the signa-
	     ture is signalled by ssh-keygen returning a zero exit status.

     -Y	sign
	     Cryptographically sign a file or some data	using a	SSH key.  When
	     signing, ssh-keygen accepts zero or more files to sign on the
	     command-line - if no files	are specified then ssh-keygen will
	     sign data presented on standard input.  Signatures	are written to
	     the path of the input file	with ".sig" appended, or to standard
	     output if the message to be signed	was read from standard input.

	     The key used for signing is specified using the -f	option and may
	     refer to either a private key, or a public	key with the private
	     half available via	ssh-agent(1).  An additional signature name-
	     space, used to prevent signature confusion	across different do-
	     mains of use (e.g.	file signing vs	email signing) must be pro-
	     vided via the -n flag.  Namespaces	are arbitrary strings, and may
	     include: "file" for file signing, "email" for email signing.  For
	     custom uses, it is	recommended to use names following a NAME-
	     SPACE@YOUR.DOMAIN pattern to generate unambiguous namespaces.

     -Y	verify
	     Request to	verify a signature generated using ssh-keygen -Y sign
	     as	described above.  When verifying a signature, ssh-keygen ac-
	     cepts a message on	standard input and a signature namespace using
	     -n.  A file containing the	corresponding signature	must also be
	     supplied using the	-s flag, along with the	identity of the	signer
	     using -I and a list of allowed signers via	the -f flag.  The for-
	     mat of the	allowed	signers	file is	documented in the ALLOWED
	     SIGNERS section below.  A file containing revoked keys can	be
	     passed using the -r flag.	The revocation file may	be a KRL or a
	     one-per-line list of public keys.	Successful verification	by an
	     authorized	signer is signalled by ssh-keygen returning a zero
	     exit status.

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

     -Z	cipher
	     Specifies the cipher to use for encryption	when writing an
	     OpenSSH-format private key	file.  The list	of available ciphers
	     may be obtained using "ssh	-Q cipher".  The default is

     -z	serial_number
	     Specifies a serial	number to be embedded in the certificate to
	     distinguish this certificate from others from the same CA.	 If
	     the serial_number is prefixed with	a `+' character, then the se-
	     rial number will be incremented for each certificate signed on a
	     single command-line.  The default serial number is	zero.

	     When generating a KRL, the	-z flag	is used	to specify a KRL ver-
	     sion number.

     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 -M generate option.  The de-
     sired length of the primes	may be specified by the	-O bits	option.	 For

	   # ssh-keygen	-M generate -O bits=2048 moduli-2048.candidates

     By	default, the search for	primes begins at a random point	in the desired
     length range.  This may be	overridden using the -O	start option, which
     specifies 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 -M screen option.  In this
     mode ssh-keygen will read candidates from standard	input (or a file spec-
     ified using the -f	option).  For example:

	   # ssh-keygen	-M screen -f moduli-2048.candidates moduli-2048

     By	default, each candidate	will be	subjected to 100 primality tests.
     This may be overridden using the -O prime-tests 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 -O
     generator 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.

     A number of options are available for moduli generation and screening via
     the -O flag:

	     Exit after	screening the specified	number of lines	while perform-
	     ing DH candidate screening.

	     Start screening at	the specified line number while	performing DH
	     candidate screening.

	     Write the last line processed to the specified file while per-
	     forming DH	candidate screening.  This will	be used	to skip	lines
	     in	the input file that have already been processed	if the job is

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

	     Specify start point (in hex) when generating candidate moduli for

	     Specify desired generator (in decimal) when testing candidate
	     moduli for	DH-GEX.

     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

     Similarly,	it is possible for the CA key to be hosted in a	ssh-agent(1).
     This is indicated by the -U flag and, again, the CA key must be identi-
     fied by its public	half.

	   $ ssh-keygen	-Us -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.

     The options that are valid	for user certificates are:

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

	     Includes an arbitrary certificate critical	option or extension.
	     The specified name	should include a domain	suffix,	e.g.
	     "".  If contents is specified then	it is included
	     as	the contents of	the extension/option encoded as	a string, oth-
	     erwise the	extension/option is created with no contents (usually
	     indicating	a flag).  Extensions may be ignored by a client	or
	     server that does not recognise them, whereas unknown critical op-
	     tions will	cause the certificate to be refused.

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

	     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 default).

	     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.

	     Do	not require signatures made using this key include demonstra-
	     tion of user presence (e.g. by having the user touch the authen-
	     ticator).	This option only makes sense for the FIDO authentica-
	     tor algorithms ecdsa-sk and ed25519-sk.

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

	     Require signatures	made using this	key indicate that the user was
	     first verified.  This option only makes sense for the FIDO	au-
	     thenticator algorithms ecdsa-sk and ed25519-sk.  Currently	PIN
	     authentication is the only	supported verification method, but
	     other methods may be supported in the future.

     At	present, no standard options are valid for host	keys.

     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 are valid	from the UNIX Epoch to
     the distant future.

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

     ssh-keygen	is able	to generate FIDO authenticator-backed keys, after
     which they	may be used much like any other	key type supported by OpenSSH,
     so	long as	the hardware authenticator is attached when the	keys are used.
     FIDO authenticators generally require the user to explicitly authorise
     operations	by touching or tapping them.  FIDO keys	consist	of two parts:
     a key handle part stored in the private key file on disk, and a per-de-
     vice private key that is unique to	each FIDO authenticator	and that can-
     not be exported from the authenticator hardware.  These are combined by
     the hardware at authentication time to derive the real key	that is	used
     to	sign authentication challenges.	 Supported key types are ecdsa-sk and

     The options that are valid	for FIDO keys are:

	     Override the default FIDO application/origin string of "ssh:".
	     This may be useful	when generating	host or	domain-specific	resi-
	     dent keys.	 The specified application string must begin with

	     Specifies a path to a challenge string that will be passed	to the
	     FIDO authenticator	during key generation.	The challenge string
	     may be used as part of an out-of-band protocol for	key enrollment
	     (a	random challenge is used by default).

     device  Explicitly	specify	a fido(4) device to use, rather	than letting
	     the authenticator middleware select one.

	     Indicate that the generated private key should not	require	touch
	     events (user presence) when making	signatures.  Note that sshd(8)
	     will refuse such signatures by default, unless overridden via an
	     authorized_keys option.

	     Indicate that the key handle should be stored on the FIDO authen-
	     ticator itself.  This makes it easier to use the authenticator on
	     multiple computers.  Resident keys	may be supported on FIDO2 au-
	     thenticators and typically	require	that a PIN be set on the au-
	     thenticator prior to generation.  Resident	keys may be loaded off
	     the authenticator using ssh-add(1).  Storing both parts of	a key
	     on	a FIDO authenticator increases the likelihood of an attacker
	     being able	to use a stolen	authenticator device.

     user    A username	to be associated with a	resident key, overriding the
	     empty default username.  Specifying a username may	be useful when
	     generating	multiple resident keys for the same application	name.

	     Indicate that this	private	key should require user	verification
	     for each signature.  Not all FIDO authenticators support this op-
	     tion.  Currently PIN authentication is the	only supported verifi-
	     cation method, but	other methods may be supported in the future.

	     May be used at key	generation time	to record the attestation data
	     returned from FIDO	authenticators during key generation.  This
	     information is potentially	sensitive.  By default,	this informa-
	     tion is discarded.

     ssh-keygen	is able	to manage OpenSSH format Key Revocation	Lists (KRLs).
     These binary files	specify	keys or	certificates to	be revoked using a
     compact format, taking as little as one bit per certificate if they are
     being revoked by serial number.

     KRLs may be generated using the -k	flag.  This option reads one or	more
     files from	the command line and generates a new KRL.  The files may ei-
     ther contain a KRL	specification (see below) or public keys, listed one
     per line.	Plain public keys are revoked by listing their hash or con-
     tents in the KRL and certificates revoked by serial number	or key ID (if
     the serial	is zero	or not available).

     Revoking keys using a KRL specification offers explicit control over the
     types of record used to revoke keys and may be used to directly revoke
     certificates by serial number or key ID without having the	complete orig-
     inal certificate on hand.	A KRL specification consists of	lines contain-
     ing one of	the following directives followed by a colon and some direc-
     tive-specific information.

     serial: serial_number[-serial_number]
	     Revokes a certificate with	the specified serial number.  Serial
	     numbers are 64-bit	values,	not including zero and may be ex-
	     pressed in	decimal, hex or	octal.	If two serial numbers are
	     specified separated by a hyphen, then the range of	serial numbers
	     including and between each	is revoked.  The CA key	must have been
	     specified on the ssh-keygen command line using the	-s option.

     id: key_id
	     Revokes a certificate with	the specified key ID string.  The CA
	     key must have been	specified on the ssh-keygen command line using
	     the -s option.

     key: public_key
	     Revokes the specified key.	 If a certificate is listed, then it
	     is	revoked	as a plain public key.

     sha1: public_key
	     Revokes the specified key by including its	SHA1 hash in the KRL.

     sha256: public_key
	     Revokes the specified key by including its	SHA256 hash in the
	     KRL.  KRLs	that revoke keys by SHA256 hash	are not	supported by
	     OpenSSH versions prior to 7.9.

     hash: fingerprint
	     Revokes a key using a fingerprint hash, as	obtained from a
	     sshd(8) authentication log	message	or the ssh-keygen -l flag.
	     Only SHA256 fingerprints are supported here and resultant KRLs
	     are not supported by OpenSSH versions prior to 7.9.

     KRLs may be updated using the -u flag in addition to -k.  When this op-
     tion is specified,	keys listed via	the command line are merged into the
     KRL, adding to those already there.

     It	is also	possible, given	a KRL, to test whether it revokes a particular
     key (or keys).  The -Q flag will query an existing	KRL, testing each key
     specified on the command line.  If	any key	listed on the command line has
     been revoked (or an error encountered) then ssh-keygen will exit with a
     non-zero exit status.  A zero exit	status will only be returned if	no key
     was revoked.

     When verifying signatures,	ssh-keygen uses	a simple list of identities
     and keys to determine whether a signature comes from an authorized
     source.  This "allowed signers" file uses a format	patterned after	the
     AUTHORIZED_KEYS FILE FORMAT described in sshd(8).	Each line of the file
     contains the following space-separated fields: principals,	options, key-
     type, base64-encoded key.	Empty lines and	lines starting with a `#' are
     ignored as	comments.

     The principals field is a pattern-list (see PATTERNS in ssh_config(5))
     consisting	of one or more comma-separated USER@DOMAIN identity patterns
     that are accepted for signing.  When verifying, the identity presented
     via the -I	option must match a principals pattern in order	for the	corre-
     sponding key to be	considered acceptable for verification.

     The options (if present) consist of comma-separated option	specifica-
     tions.  No	spaces are permitted, except within double quotes.  The	fol-
     lowing option specifications are supported	(note that option keywords are

	     Indicates that this key is	accepted as a certificate authority
	     (CA) and that certificates	signed by this CA may be accepted for

	     Specifies a pattern-list of namespaces that are accepted for this
	     key.  If this option is present, the signature namespace embedded
	     in	the signature object and presented on the verification com-
	     mand-line must match the specified	list before the	key will be
	     considered	acceptable.

	     Indicates that the	key is valid for use at	or after the specified
	     timestamp,	which may be a date or time in the YYYYMMDD[Z] or
	     YYYYMMDDHHMM[SS][Z] formats.  Dates and times will	be interpreted
	     in	the current system time	zone unless suffixed with a Z charac-
	     ter, which	causes them to be interpreted in the UTC time zone.

	     Indicates that the	key is valid for use at	or before the speci-
	     fied timestamp.

     When verifying signatures made by certificates, the expected principal
     name must match both the principals pattern in the	allowed	signers	file
     and the principals	embedded in the	certificate itself.

     An	example	allowed	signers	file:

	# Comments allowed at start of line, ssh-rsa AAAAX1...
	# A certificate	authority, trusted for all principals in a domain.
	* cert-authority ssh-ed25519 AAAB4...
	# A key	that is	accepted only for file signing. namespaces="file" ssh-ed25519	AAA41...

	     Specifies a path to a library that	will be	used when loading any
	     FIDO authenticator-hosted keys, overriding	the default of using
	     the built-in USB HID support.

	     Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, au-
	     thenticator-hosted	Ed25519	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 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 pri-
	     vate key.	ssh(1) will read this file when	a login	attempt	is

	     Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, au-
	     thenticator-hosted	Ed25519	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.

FreeBSD	13.0		       February	10, 2023		  FreeBSD 13.0


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