1SSH-KEYGEN(1) BSD General Commands Manual SSH-KEYGEN(1)
2
4 ssh-keygen — OpenSSH authentication key utility
5
7 ssh-keygen [-q] [-a rounds] [-b bits] [-C comment] [-f output_keyfile]
8 [-m format] [-N new_passphrase] [-O option]
9 [-t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa]
10 [-w provider]
11 ssh-keygen -p [-a rounds] [-f keyfile] [-m format] [-N new_passphrase]
12 [-P old_passphrase]
13 ssh-keygen -i [-f input_keyfile] [-m key_format]
14 ssh-keygen -e [-f input_keyfile] [-m key_format]
15 ssh-keygen -y [-f input_keyfile]
16 ssh-keygen -c [-a rounds] [-C comment] [-f keyfile] [-P passphrase]
17 ssh-keygen -l [-v] [-E fingerprint_hash] [-f input_keyfile]
18 ssh-keygen -B [-f input_keyfile]
19 ssh-keygen -D pkcs11
20 ssh-keygen -F hostname [-lv] [-f known_hosts_file]
21 ssh-keygen -H [-f known_hosts_file]
22 ssh-keygen -K [-a rounds] [-w provider]
23 ssh-keygen -R hostname [-f known_hosts_file]
24 ssh-keygen -r hostname [-g] [-f input_keyfile]
25 ssh-keygen -M generate [-O option] output_file
26 ssh-keygen -M screen [-f input_file] [-O option] output_file
27 ssh-keygen -I certificate_identity -s ca_key [-hU] [-D pkcs11_provider]
28 [-n principals] [-O option] [-V validity_interval]
29 [-z serial_number] file ...
30 ssh-keygen -L [-f input_keyfile]
31 ssh-keygen -A [-a rounds] [-f prefix_path]
32 ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number]
33 file ...
34 ssh-keygen -Q [-l] -f krl_file file ...
35 ssh-keygen -Y find-principals -s signature_file -f allowed_signers_file
36 ssh-keygen -Y check-novalidate -n namespace -s signature_file
37 ssh-keygen -Y sign -f key_file -n namespace file ...
38 ssh-keygen -Y verify -f allowed_signers_file -I signer_identity -n
39 namespace -s signature_file [-r revocation_file]
40
42 ssh-keygen generates, manages and converts authentication keys for
43 ssh(1). ssh-keygen can create keys for use by SSH protocol version 2.
44 The type of key to be generated is specified with the -t option. If
46 invoked without any arguments, ssh-keygen will generate an RSA key.
47 ssh-keygen is also used to generate groups for use in Diffie-Hellman
49 group exchange (DH-GEX). See the MODULI GENERATION section for details.
50 Finally, ssh-keygen can be used to generate and update Key Revocation
52 Lists, and to test whether given keys have been revoked by one. See the
53 KEY REVOCATION LISTS section for details.
54 Normally each user wishing to use SSH with public key authentication runs
56 this once to create the authentication key in ~/.ssh/id_dsa,
57 ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
58 ~/.ssh/id_ed25519_sk or ~/.ssh/id_rsa. Additionally, the system adminis‐
59 trator may use this to generate host keys, as seen in /etc/rc.
60 Normally this program generates the key and asks for a file in which to
62 store the private key. The public key is stored in a file with the same
63 name but “.pub” appended. The program also asks for a passphrase. The
64 passphrase may be empty to indicate no passphrase (host keys must have an
65 empty passphrase), or it may be a string of arbitrary length. A
66 passphrase is similar to a password, except it can be a phrase with a
67 series of words, punctuation, numbers, whitespace, or any string of char‐
68 acters you want. Good passphrases are 10-30 characters long, are not
69 simple sentences or otherwise easily guessable (English prose has only
70 1-2 bits of entropy per character, and provides very bad passphrases),
71 and contain a mix of upper and lowercase letters, numbers, and non-
72 alphanumeric characters. The passphrase can be changed later by using
73 the -p option.
74 There is no way to recover a lost passphrase. If the passphrase is lost
76 or forgotten, a new key must be generated and the corresponding public
77 key copied to other machines.
78 ssh-keygen will by default write keys in an OpenSSH-specific format.
80 This format is preferred as it offers better protection for keys at rest
81 as well as allowing storage of key comments within the private key file
82 itself. The key comment may be useful to help identify the key. The
83 comment is initialized to “user@host” when the key is created, but can be
84 changed using the -c option.
85 It is still possible for ssh-keygen to write the previously-used PEM for‐
87 mat private keys using the -m flag. This may be used when generating new
88 keys, and existing new-format keys may be converted using this option in
89 conjunction with the -p (change passphrase) flag.
90 After a key is generated, ssh-keygen will ask where the keys should be
92 placed to be activated.
93 The options are as follows:
95 -A For each of the key types (rsa, dsa, ecdsa and ed25519) for which
97 host keys do not exist, generate the host keys with the default
98 key file path, an empty passphrase, default bits for the key
99 type, and default comment. If -f has also been specified, its
100 argument is used as a prefix to the default path for the result‐
101 ing host key files. This is used by /etc/rc to generate new host
102 keys.
103 -a rounds
105 When saving a private key, this option specifies the number of
106 KDF (key derivation function) rounds used. Higher numbers result
107 in slower passphrase verification and increased resistance to
108 brute-force password cracking (should the keys be stolen). The
109 default is 16 rounds.
110 -B Show the bubblebabble digest of specified private or public key
112 file.
113 -b bits
115 Specifies the number of bits in the key to create. For RSA keys,
116 the minimum size is 1024 bits and the default is 3072 bits. Gen‐
117 erally, 3072 bits is considered sufficient. DSA keys must be
118 exactly 1024 bits as specified by FIPS 186-2. For ECDSA keys,
119 the -b flag determines the key length by selecting from one of
120 three elliptic curve sizes: 256, 384 or 521 bits. Attempting to
121 use bit lengths other than these three values for ECDSA keys will
122 fail. ECDSA-SK, Ed25519 and Ed25519-SK keys have a fixed length
123 and the -b flag will be ignored.
124 -C comment
126 Provides a new comment.
127 -c Requests changing the comment in the private and public key
129 files. The program will prompt for the file containing the pri‐
130 vate keys, for the passphrase if the key has one, and for the new
131 comment.
132 -D pkcs11
134 Download the public keys provided by the PKCS#11 shared library
135 pkcs11. When used in combination with -s, this option indicates
136 that a CA key resides in a PKCS#11 token (see the CERTIFICATES
137 section for details).
138 -E fingerprint_hash
140 Specifies the hash algorithm used when displaying key finger‐
141 prints. Valid options are: “md5” and “sha256”. The default is
142 “sha256”.
143 -e This option will read a private or public OpenSSH key file and
145 print to stdout a public key in one of the formats specified by
146 the -m option. The default export format is “RFC4716”. This
147 option allows exporting OpenSSH keys for use by other programs,
148 including several commercial SSH implementations.
149 -F hostname | [hostname]:port
151 Search for the specified hostname (with optional port number) in
152 a known_hosts file, listing any occurrences found. This option
153 is useful to find hashed host names or addresses and may also be
154 used in conjunction with the -H option to print found keys in a
155 hashed format.
156 -f filename
158 Specifies the filename of the key file.
159 -g Use generic DNS format when printing fingerprint resource records
161 using the -r command.
162 -H Hash a known_hosts file. This replaces all hostnames and
164 addresses with hashed representations within the specified file;
165 the original content is moved to a file with a .old suffix.
166 These hashes may be used normally by ssh and sshd, but they do
167 not reveal identifying information should the file's contents be
168 disclosed. This option will not modify existing hashed hostnames
169 and is therefore safe to use on files that mix hashed and non-
170 hashed names.
171 -h When signing a key, create a host certificate instead of a user
173 certificate. Please see the CERTIFICATES section for details.
174 -I certificate_identity
176 Specify the key identity when signing a public key. Please see
177 the CERTIFICATES section for details.
178 -i This option will read an unencrypted private (or public) key file
180 in the format specified by the -m option and print an OpenSSH
181 compatible private (or public) key to stdout. This option allows
182 importing keys from other software, including several commercial
183 SSH implementations. The default import format is “RFC4716”.
184 -K Download resident keys from a FIDO authenticator. Public and
186 private key files will be written to the current directory for
187 each downloaded key. If multiple FIDO authenticators are
188 attached, keys will be downloaded from the first touched authen‐
189 ticator.
190 -k Generate a KRL file. In this mode, ssh-keygen will generate a
192 KRL file at the location specified via the -f flag that revokes
193 every key or certificate presented on the command line.
194 Keys/certificates to be revoked may be specified by public key
195 file or using the format described in the KEY REVOCATION LISTS
196 section.
197 -L Prints the contents of one or more certificates.
199 -l Show fingerprint of specified public key file. For RSA and DSA
201 keys ssh-keygen tries to find the matching public key file and
202 prints its fingerprint. If combined with -v, a visual ASCII art
203 representation of the key is supplied with the fingerprint.
204 -M generate
206 Generate candidate Diffie-Hellman Group Exchange (DH-GEX) parame‐
207 ters for eventual use by the ‘diffie-hellman-group-exchange-*’
208 key exchange methods. The numbers generated by this operation
209 must be further screened before use. See the MODULI GENERATION
210 section for more information.
211 -M screen
213 Screen candidate parameters for Diffie-Hellman Group Exchange.
214 This will accept a list of candidate numbers and test that they
215 are safe (Sophie Germain) primes with acceptable group genera‐
216 tors. The results of this operation may be added to the
217 /etc/ssh/moduli file. See the MODULI GENERATION section for more
218 information.
219 -m key_format
221 Specify a key format for key generation, the -i (import), -e
222 (export) conversion options, and the -p change passphrase opera‐
223 tion. The latter may be used to convert between OpenSSH private
224 key and PEM private key formats. The supported key formats are:
225 “RFC4716” (RFC 4716/SSH2 public or private key), “PKCS8” (PKCS8
226 public or private key) or “PEM” (PEM public key). By default
227 OpenSSH will write newly-generated private keys in its own for‐
228 mat, but when converting public keys for export the default for‐
229 mat is “RFC4716”. Setting a format of “PEM” when generating or
230 updating a supported private key type will cause the key to be
231 stored in the legacy PEM private key format.
232 -N new_passphrase
234 Provides the new passphrase.
235 -n principals
237 Specify one or more principals (user or host names) to be
238 included in a certificate when signing a key. Multiple princi‐
239 pals may be specified, separated by commas. Please see the
240 CERTIFICATES section for details.
241 -O option
243 Specify a key/value option. These are specific to the operation
244 that ssh-keygen has been requested to perform.
245 When signing certificates, one of the options listed in the
247 CERTIFICATES section may be specified here.
248 When performing moduli generation or screening, one of the
250 options listed in the MODULI GENERATION section may be specified.
251 When generating a key that will be hosted on a FIDO authentica‐
253 tor, this flag may be used to specify key-specific options.
254 Those supported at present are:
255 application
257 Override the default FIDO application/origin string of
258 “ssh:”. This may be useful when generating host or
259 domain-specific resident keys. The specified application
260 string must begin with “ssh:”.
261 challenge=path
263 Specifies a path to a challenge string that will be
264 passed to the FIDO token during key generation. The
265 challenge string may be used as part of an out-of-band
266 protocol for key enrollment (a random challenge is used
267 by default).
268 device Explicitly specify a fido(4) device to use, rather than
270 letting the token middleware select one.
271 no-touch-required
273 Indicate that the generated private key should not
274 require touch events (user presence) when making signa‐
275 tures. Note that sshd(8) will refuse such signatures by
276 default, unless overridden via an authorized_keys option.
277 resident
279 Indicate that the key should be stored on the FIDO
280 authenticator itself. Resident keys may be supported on
281 FIDO2 tokens and typically require that a PIN be set on
282 the token prior to generation. Resident keys may be
283 loaded off the token using ssh-add(1).
284 user A username to be associated with a resident key, overrid‐
286 ing the empty default username. Specifying a username
287 may be useful when generating multiple resident keys for
288 the same application name.
289 verify-required
291 Indicate that this private key should require user veri‐
292 fication for each signature. Not all FIDO tokens support
293 this option. Currently PIN authentication is the only
294 supported verification method, but other methods may be
295 supported in the future.
296 write-attestation=path
298 May be used at key generation time to record the attesta‐
299 tion data returned from FIDO tokens during key genera‐
300 tion. Please note that this information is potentially
301 sensitive. By default, this information is discarded.
302 The -O option may be specified multiple times.
304 -P passphrase
306 Provides the (old) passphrase.
307 -p Requests changing the passphrase of a private key file instead of
309 creating a new private key. The program will prompt for the file
310 containing the private key, for the old passphrase, and twice for
311 the new passphrase.
312 -Q Test whether keys have been revoked in a KRL. If the -l option
314 is also specified then the contents of the KRL will be printed.
315 -q Silence ssh-keygen.
317 -R hostname | [hostname]:port
319 Removes all keys belonging to the specified hostname (with
320 optional port number) from a known_hosts file. This option is
321 useful to delete hashed hosts (see the -H option above).
322 -r hostname
324 Print the SSHFP fingerprint resource record named hostname for
325 the specified public key file.
326 -s ca_key
328 Certify (sign) a public key using the specified CA key. Please
329 see the CERTIFICATES section for details.
330 When generating a KRL, -s specifies a path to a CA public key
332 file used to revoke certificates directly by key ID or serial
333 number. See the KEY REVOCATION LISTS section for details.
334 -t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa
336 Specifies the type of key to create. The possible values are
337 “dsa”, “ecdsa”, “ecdsa-sk”, “ed25519”, “ed25519-sk”, or “rsa”.
338 This flag may also be used to specify the desired signature type
340 when signing certificates using an RSA CA key. The available RSA
341 signature variants are “ssh-rsa” (SHA1 signatures, not recom‐
342 mended), “rsa-sha2-256”, and “rsa-sha2-512” (the default).
343 -U When used in combination with -s, this option indicates that a CA
345 key resides in a ssh-agent(1). See the CERTIFICATES section for
346 more information.
347 -u Update a KRL. When specified with -k, keys listed via the com‐
349 mand line are added to the existing KRL rather than a new KRL
350 being created.
351 -V validity_interval
353 Specify a validity interval when signing a certificate. A valid‐
354 ity interval may consist of a single time, indicating that the
355 certificate is valid beginning now and expiring at that time, or
356 may consist of two times separated by a colon to indicate an
357 explicit time interval.
358 The start time may be specified as the string “always” to indi‐
360 cate the certificate has no specified start time, a date in
361 YYYYMMDD format, a time in YYYYMMDDHHMM[SS] format, a relative
362 time (to the current time) consisting of a minus sign followed by
363 an interval in the format described in the TIME FORMATS section
364 of sshd_config(5).
365 The end time may be specified as a YYYYMMDD date, a YYYYMMD‐
367 DHHMM[SS] time, a relative time starting with a plus character or
368 the string “forever” to indicate that the certificate has no
369 expiry date.
370 For example: “+52w1d” (valid from now to 52 weeks and one day
372 from now), “-4w:+4w” (valid from four weeks ago to four weeks
373 from now), “20100101123000:20110101123000” (valid from 12:30 PM,
374 January 1st, 2010 to 12:30 PM, January 1st, 2011), “-1d:20110101”
375 (valid from yesterday to midnight, January 1st, 2011).
376 “-1m:forever” (valid from one minute ago and never expiring).
377 -v Verbose mode. Causes ssh-keygen to print debugging messages
379 about its progress. This is helpful for debugging moduli genera‐
380 tion. Multiple -v options increase the verbosity. The maximum
381 is 3.
382 -w provider
384 Specifies a path to a library that will be used when creating
385 FIDO authenticator-hosted keys, overriding the default of using
386 the internal USB HID support.
387 -Y find-principals
389 Find the principal(s) associated with the public key of a signa‐
390 ture, provided using the -s flag in an authorized signers file
391 provided using the -f flag. The format of the allowed signers
392 file is documented in the ALLOWED SIGNERS section below. If one
393 or more matching principals are found, they are returned on stan‐
394 dard output.
395 -Y check-novalidate
397 Checks that a signature generated using ssh-keygen -Y sign has a
398 valid structure. This does not validate if a signature comes
399 from an authorized signer. When testing a signature, ssh-keygen
400 accepts a message on standard input and a signature namespace
401 using -n. A file containing the corresponding signature must
402 also be supplied using the -s flag. Successful testing of the
403 signature is signalled by ssh-keygen returning a zero exit sta‐
404 tus.
405 -Y sign
407 Cryptographically sign a file or some data using a SSH key. When
408 signing, ssh-keygen accepts zero or more files to sign on the
409 command-line - if no files are specified then ssh-keygen will
410 sign data presented on standard input. Signatures are written to
411 the path of the input file with “.sig” appended, or to standard
412 output if the message to be signed was read from standard input.
413 The key used for signing is specified using the -f option and may
415 refer to either a private key, or a public key with the private
416 half available via ssh-agent(1). An additional signature names‐
417 pace, used to prevent signature confusion across different
418 domains of use (e.g. file signing vs email signing) must be pro‐
419 vided via the -n flag. Namespaces are arbitrary strings, and may
420 include: “file” for file signing, “email” for email signing. For
421 custom uses, it is recommended to use names following a NAMES‐
422 PACE@YOUR.DOMAIN pattern to generate unambiguous namespaces.
423 -Y verify
425 Request to verify a signature generated using ssh-keygen -Y sign
426 as described above. When verifying a signature, ssh-keygen
427 accepts a message on standard input and a signature namespace
428 using -n. A file containing the corresponding signature must
429 also be supplied using the -s flag, along with the identity of
430 the signer using -I and a list of allowed signers via the -f
431 flag. The format of the allowed signers file is documented in
432 the ALLOWED SIGNERS section below. A file containing revoked
433 keys can be passed using the -r flag. The revocation file may be
434 a KRL or a one-per-line list of public keys. Successful verifi‐
435 cation by an authorized signer is signalled by ssh-keygen return‐
436 ing a zero exit status.
437 -y This option will read a private OpenSSH format file and print an
439 OpenSSH public key to stdout.
440 -z serial_number
442 Specifies a serial number to be embedded in the certificate to
443 distinguish this certificate from others from the same CA. If
444 the serial_number is prefixed with a ‘+’ character, then the
445 serial number will be incremented for each certificate signed on
446 a single command-line. The default serial number is zero.
447 When generating a KRL, the -z flag is used to specify a KRL ver‐
449 sion number.
450
452 ssh-keygen may be used to generate groups for the Diffie-Hellman Group
453 Exchange (DH-GEX) protocol. Generating these groups is a two-step
454 process: first, candidate primes are generated using a fast, but memory
455 intensive process. These candidate primes are then tested for suitabil‐
456 ity (a CPU-intensive process).
457 Generation of primes is performed using the -M generate option. The
459 desired length of the primes may be specified by the -O bits option. For
460 example:
461 # ssh-keygen -M generate -O bits=2048 moduli-2048.candidates
463 By default, the search for primes begins at a random point in the desired
465 length range. This may be overridden using the -O start option, which
466 specifies a different start point (in hex).
467 Once a set of candidates have been generated, they must be screened for
469 suitability. This may be performed using the -M screen option. In this
470 mode ssh-keygen will read candidates from standard input (or a file spec‐
471 ified using the -f option). For example:
472 # ssh-keygen -M screen -f moduli-2048.candidates moduli-2048
474 By default, each candidate will be subjected to 100 primality tests.
476 This may be overridden using the -O prime-tests option. The DH generator
477 value will be chosen automatically for the prime under consideration. If
478 a specific generator is desired, it may be requested using the -O
479 generator option. Valid generator values are 2, 3, and 5.
480 Screened DH groups may be installed in /etc/ssh/moduli. It is important
482 that this file contains moduli of a range of bit lengths and that both
483 ends of a connection share common moduli.
484 A number of options are available for moduli generation and screening via
486 the -O flag:
487 lines=number
489 Exit after screening the specified number of lines while perform‐
490 ing DH candidate screening.
491 start-line=line-number
493 Start screening at the specified line number while performing DH
494 candidate screening.
495 checkpoint=filename
497 Write the last line processed to the specified file while per‐
498 forming DH candidate screening. This will be used to skip lines
499 in the input file that have already been processed if the job is
500 restarted.
501 memory=mbytes
503 Specify the amount of memory to use (in megabytes) when generat‐
504 ing candidate moduli for DH-GEX.
505 start=hex-value
507 Specify start point (in hex) when generating candidate moduli for
508 DH-GEX.
509 generator=value
511 Specify desired generator (in decimal) when testing candidate
512 moduli for DH-GEX.
513
515 ssh-keygen supports signing of keys to produce certificates that may be
516 used for user or host authentication. Certificates consist of a public
517 key, some identity information, zero or more principal (user or host)
518 names and a set of options that are signed by a Certification Authority
519 (CA) key. Clients or servers may then trust only the CA key and verify
520 its signature on a certificate rather than trusting many user/host keys.
521 Note that OpenSSH certificates are a different, and much simpler, format
522 to the X.509 certificates used in ssl(8).
523 ssh-keygen supports two types of certificates: user and host. User cer‐
525 tificates authenticate users to servers, whereas host certificates
526 authenticate server hosts to users. To generate a user certificate:
527 $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
529 The resultant certificate will be placed in /path/to/user_key-cert.pub.
531 A host certificate requires the -h option:
532 $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
534 The host certificate will be output to /path/to/host_key-cert.pub.
536 It is possible to sign using a CA key stored in a PKCS#11 token by pro‐
538 viding the token library using -D and identifying the CA key by providing
539 its public half as an argument to -s:
540 $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub
542 Similarly, it is possible for the CA key to be hosted in a ssh-agent(1).
544 This is indicated by the -U flag and, again, the CA key must be identi‐
545 fied by its public half.
546 $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub
548 In all cases, key_id is a "key identifier" that is logged by the server
550 when the certificate is used for authentication.
551 Certificates may be limited to be valid for a set of principal
553 (user/host) names. By default, generated certificates are valid for all
554 users or hosts. To generate a certificate for a specified set of princi‐
555 pals:
556 $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
558 $ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub
559 Additional limitations on the validity and use of user certificates may
561 be specified through certificate options. A certificate option may dis‐
562 able features of the SSH session, may be valid only when presented from
563 particular source addresses or may force the use of a specific command.
564 The options that are valid for user certificates are:
566 clear Clear all enabled permissions. This is useful for clearing the
568 default set of permissions so permissions may be added individu‐
569 ally.
570 critical:name[=contents]
572 extension:name[=contents]
573 Includes an arbitrary certificate critical option or extension.
574 The specified name should include a domain suffix, e.g.
575 “name@example.com”. If contents is specified then it is included
576 as the contents of the extension/option encoded as a string, oth‐
577 erwise the extension/option is created with no contents (usually
578 indicating a flag). Extensions may be ignored by a client or
579 server that does not recognise them, whereas unknown critical
580 options will cause the certificate to be refused.
581 force-command=command
583 Forces the execution of command instead of any shell or command
584 specified by the user when the certificate is used for authenti‐
585 cation.
586 no-agent-forwarding
588 Disable ssh-agent(1) forwarding (permitted by default).
589 no-port-forwarding
591 Disable port forwarding (permitted by default).
592 no-pty Disable PTY allocation (permitted by default).
594 no-user-rc
596 Disable execution of ~/.ssh/rc by sshd(8) (permitted by default).
597 no-x11-forwarding
599 Disable X11 forwarding (permitted by default).
600 permit-agent-forwarding
602 Allows ssh-agent(1) forwarding.
603 permit-port-forwarding
605 Allows port forwarding.
606 permit-pty
608 Allows PTY allocation.
609 permit-user-rc
611 Allows execution of ~/.ssh/rc by sshd(8).
612 permit-X11-forwarding
614 Allows X11 forwarding.
615 no-touch-required
617 Do not require signatures made using this key include demonstra‐
618 tion of user presence (e.g. by having the user touch the authen‐
619 ticator). This option only makes sense for the FIDO authentica‐
620 tor algorithms ecdsa-sk and ed25519-sk.
621 source-address=address_list
623 Restrict the source addresses from which the certificate is con‐
624 sidered valid. The address_list is a comma-separated list of one
625 or more address/netmask pairs in CIDR format.
626 verify-required
628 Require signatures made using this key indicate that the user was
629 first verified. This option only makes sense for the FIDO
630 authenticator algorithms ecdsa-sk and ed25519-sk. Currently PIN
631 authentication is the only supported verification method, but
632 other methods may be supported in the future.
633 At present, no standard options are valid for host keys.
635 Finally, certificates may be defined with a validity lifetime. The -V
637 option allows specification of certificate start and end times. A cer‐
638 tificate that is presented at a time outside this range will not be con‐
639 sidered valid. By default, certificates are valid from UNIX Epoch to the
640 distant future.
641 For certificates to be used for user or host authentication, the CA pub‐
643 lic key must be trusted by sshd(8) or ssh(1). Please refer to those man‐
644 ual pages for details.
645
647 ssh-keygen is able to manage OpenSSH format Key Revocation Lists (KRLs).
648 These binary files specify keys or certificates to be revoked using a
649 compact format, taking as little as one bit per certificate if they are
650 being revoked by serial number.
651 KRLs may be generated using the -k flag. This option reads one or more
653 files from the command line and generates a new KRL. The files may
654 either contain a KRL specification (see below) or public keys, listed one
655 per line. Plain public keys are revoked by listing their hash or con‐
656 tents in the KRL and certificates revoked by serial number or key ID (if
657 the serial is zero or not available).
658 Revoking keys using a KRL specification offers explicit control over the
660 types of record used to revoke keys and may be used to directly revoke
661 certificates by serial number or key ID without having the complete orig‐
662 inal certificate on hand. A KRL specification consists of lines contain‐
663 ing one of the following directives followed by a colon and some direc‐
664 tive-specific information.
665 serial: serial_number[-serial_number]
667 Revokes a certificate with the specified serial number. Serial
668 numbers are 64-bit values, not including zero and may be
669 expressed in decimal, hex or octal. If two serial numbers are
670 specified separated by a hyphen, then the range of serial numbers
671 including and between each is revoked. The CA key must have been
672 specified on the ssh-keygen command line using the -s option.
673 id: key_id
675 Revokes a certificate with the specified key ID string. The CA
676 key must have been specified on the ssh-keygen command line using
677 the -s option.
678 key: public_key
680 Revokes the specified key. If a certificate is listed, then it
681 is revoked as a plain public key.
682 sha1: public_key
684 Revokes the specified key by including its SHA1 hash in the KRL.
685 sha256: public_key
687 Revokes the specified key by including its SHA256 hash in the
688 KRL. KRLs that revoke keys by SHA256 hash are not supported by
689 OpenSSH versions prior to 7.9.
690 hash: fingerprint
692 Revokes a key using a fingerprint hash, as obtained from a
693 sshd(8) authentication log message or the ssh-keygen -l flag.
694 Only SHA256 fingerprints are supported here and resultant KRLs
695 are not supported by OpenSSH versions prior to 7.9.
696 KRLs may be updated using the -u flag in addition to -k. When this
698 option is specified, keys listed via the command line are merged into the
699 KRL, adding to those already there.
700 It is also possible, given a KRL, to test whether it revokes a particular
702 key (or keys). The -Q flag will query an existing KRL, testing each key
703 specified on the command line. If any key listed on the command line has
704 been revoked (or an error encountered) then ssh-keygen will exit with a
705 non-zero exit status. A zero exit status will only be returned if no key
706 was revoked.
707
709 When verifying signatures, ssh-keygen uses a simple list of identities
710 and keys to determine whether a signature comes from an authorized
711 source. This "allowed signers" file uses a format patterned after the
712 AUTHORIZED_KEYS FILE FORMAT described in sshd(8). Each line of the file
713 contains the following space-separated fields: principals, options, key‐
714 type, base64-encoded key. Empty lines and lines starting with a ‘#’ are
715 ignored as comments.
716 The principals field is a pattern-list (See PATTERNS in ssh_config(5))
718 consisting of one or more comma-separated USER@DOMAIN identity patterns
719 that are accepted for signing. When verifying, the identity presented
720 via the -I option must match a principals pattern in order for the corre‐
721 sponding key to be considered acceptable for verification.
722 The options (if present) consist of comma-separated option specifica‐
724 tions. No spaces are permitted, except within double quotes. The fol‐
725 lowing option specifications are supported (note that option keywords are
726 case-insensitive):
727 cert-authority
729 Indicates that this key is accepted as a certificate authority
730 (CA) and that certificates signed by this CA may be accepted for
731 verification.
732 namespaces="namespace-list"
734 Specifies a pattern-list of namespaces that are accepted for this
735 key. If this option is present, the signature namespace embedded
736 in the signature object and presented on the verification com‐
737 mand-line must match the specified list before the key will be
738 considered acceptable.
739 When verifying signatures made by certificates, the expected principal
741 name must match both the principals pattern in the allowed signers file
742 and the principals embedded in the certificate itself.
743 An example allowed signers file:
745 # Comments allowed at start of line
747 user1@example.com,user2@example.com ssh-rsa AAAAX1...
748 # A certificate authority, trusted for all principals in a domain.
749 *@example.com cert-authority ssh-ed25519 AAAB4...
750 # A key that is accepted only for file signing.
751 user2@example.com namespaces="file" ssh-ed25519 AAA41...
752
754 SSH_SK_PROVIDER
755 Specifies a path to a library that will be used when loading any
756 FIDO authenticator-hosted keys, overriding the default of using
757 the built-in USB HID support.
758
760 ~/.ssh/id_dsa
761 ~/.ssh/id_ecdsa
762 ~/.ssh/id_ecdsa_sk
763 ~/.ssh/id_ed25519
764 ~/.ssh/id_ed25519_sk
765 ~/.ssh/id_rsa
766 Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519,
767 authenticator-hosted Ed25519 or RSA authentication identity of
768 the user. This file should not be readable by anyone but the
769 user. It is possible to specify a passphrase when generating the
770 key; that passphrase will be used to encrypt the private part of
771 this file using 128-bit AES. This file is not automatically
772 accessed by ssh-keygen but it is offered as the default file for
773 the private key. ssh(1) will read this file when a login attempt
774 is made.
775 ~/.ssh/id_dsa.pub
777 ~/.ssh/id_ecdsa.pub
778 ~/.ssh/id_ecdsa_sk.pub
779 ~/.ssh/id_ed25519.pub
780 ~/.ssh/id_ed25519_sk.pub
781 ~/.ssh/id_rsa.pub
782 Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519,
783 authenticator-hosted Ed25519 or RSA public key for authentica‐
784 tion. The contents of this file should be added to
785 ~/.ssh/authorized_keys on all machines where the user wishes to
786 log in using public key authentication. There is no need to keep
787 the contents of this file secret.
788 /etc/ssh/moduli
790 Contains Diffie-Hellman groups used for DH-GEX. The file format
791 is described in moduli(5).
792
794 ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
795 The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006.
797
799 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
800 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
801 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
802 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
803 versions 1.5 and 2.0.
804BSD September 9, 2020 BSD