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] [-Z cipher]
11 ssh-keygen -p [-a rounds] [-f keyfile] [-m format] [-N new_passphrase]
12 [-P old_passphrase] [-Z cipher]
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 [-O option] -s signature_file -f
36 allowed_signers_file
37 ssh-keygen -Y check-novalidate [-O option] -n namespace -s signature_file
38 ssh-keygen -Y sign -f key_file -n namespace file ...
39 ssh-keygen -Y verify [-O option] -f allowed_signers_file -I
40 signer_identity -n namespace -s signature_file
41 [-r revocation_file]
42
44 ssh-keygen generates, manages and converts authentication keys for
45 ssh(1). ssh-keygen can create keys for use by SSH protocol version 2.
46 The type of key to be generated is specified with the -t option. If in‐
48 voked without any arguments, ssh-keygen will generate an RSA key.
49 ssh-keygen is also used to generate groups for use in Diffie-Hellman
51 group exchange (DH-GEX). See the MODULI GENERATION section for details.
52 Finally, ssh-keygen can be used to generate and update Key Revocation
54 Lists, and to test whether given keys have been revoked by one. See the
55 KEY REVOCATION LISTS section for details.
56 Normally each user wishing to use SSH with public key authentication runs
58 this once to create the authentication key in ~/.ssh/id_dsa,
59 ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
60 ~/.ssh/id_ed25519_sk or ~/.ssh/id_rsa. Additionally, the system adminis‐
61 trator may use this to generate host keys, as seen in /etc/rc.
62 Normally this program generates the key and asks for a file in which to
64 store the private key. The public key is stored in a file with the same
65 name but “.pub” appended. The program also asks for a passphrase. The
66 passphrase may be empty to indicate no passphrase (host keys must have an
67 empty passphrase), or it may be a string of arbitrary length. A
68 passphrase is similar to a password, except it can be a phrase with a se‐
69 ries of words, punctuation, numbers, whitespace, or any string of charac‐
70 ters you want. Good passphrases are 10-30 characters long, are not sim‐
71 ple sentences or otherwise easily guessable (English prose has only 1-2
72 bits of entropy per character, and provides very bad passphrases), and
73 contain a mix of upper and lowercase letters, numbers, and non-alphanu‐
74 meric characters. The passphrase can be changed later by using the -p
75 option.
76 There is no way to recover a lost passphrase. If the passphrase is lost
78 or forgotten, a new key must be generated and the corresponding public
79 key copied to other machines.
80 ssh-keygen will by default write keys in an OpenSSH-specific format.
82 This format is preferred as it offers better protection for keys at rest
83 as well as allowing storage of key comments within the private key file
84 itself. The key comment may be useful to help identify the key. The
85 comment is initialized to “user@host” when the key is created, but can be
86 changed using the -c option.
87 It is still possible for ssh-keygen to write the previously-used PEM for‐
89 mat private keys using the -m flag. This may be used when generating new
90 keys, and existing new-format keys may be converted using this option in
91 conjunction with the -p (change passphrase) flag.
92 After a key is generated, ssh-keygen will ask where the keys should be
94 placed to be activated.
95 The options are as follows:
97 -A For each of the key types (rsa, dsa, ecdsa and ed25519) for which
99 host keys do not exist, generate the host keys with the default
100 key file path, an empty passphrase, default bits for the key
101 type, and default comment. If -f has also been specified, its
102 argument is used as a prefix to the default path for the result‐
103 ing host key files. This is used by /etc/rc to generate new host
104 keys.
105 -a rounds
107 When saving a private key, this option specifies the number of
108 KDF (key derivation function, currently bcrypt_pbkdf(3)) rounds
109 used. Higher numbers result in slower passphrase verification
110 and increased resistance to brute-force password cracking (should
111 the keys be stolen). The default is 16 rounds.
112 -B Show the bubblebabble digest of specified private or public key
114 file.
115 -b bits
117 Specifies the number of bits in the key to create. For RSA keys,
118 the minimum size is 1024 bits and the default is 3072 bits. Gen‐
119 erally, 3072 bits is considered sufficient. DSA keys must be ex‐
120 actly 1024 bits as specified by FIPS 186-2. For ECDSA keys, the
121 -b flag determines the key length by selecting from one of three
122 elliptic curve sizes: 256, 384 or 521 bits. Attempting to use
123 bit lengths other than these three values for ECDSA keys will
124 fail. ECDSA-SK, Ed25519 and Ed25519-SK keys have a fixed length
125 and the -b flag will be ignored.
126 -C comment
128 Provides a new comment.
129 -c Requests changing the comment in the private and public key
131 files. The program will prompt for the file containing the pri‐
132 vate keys, for the passphrase if the key has one, and for the new
133 comment.
134 -D pkcs11
136 Download the public keys provided by the PKCS#11 shared library
137 pkcs11. When used in combination with -s, this option indicates
138 that a CA key resides in a PKCS#11 token (see the CERTIFICATES
139 section for details).
140 -E fingerprint_hash
142 Specifies the hash algorithm used when displaying key finger‐
143 prints. Valid options are: “md5” and “sha256”. The default is
144 “sha256”.
145 -e This option will read a private or public OpenSSH key file and
147 print to stdout a public key in one of the formats specified by
148 the -m option. The default export format is “RFC4716”. This op‐
149 tion allows exporting OpenSSH keys for use by other programs, in‐
150 cluding several commercial SSH implementations.
151 -F hostname | [hostname]:port
153 Search for the specified hostname (with optional port number) in
154 a known_hosts file, listing any occurrences found. This option
155 is useful to find hashed host names or addresses and may also be
156 used in conjunction with the -H option to print found keys in a
157 hashed format.
158 -f filename
160 Specifies the filename of the key file.
161 -g Use generic DNS format when printing fingerprint resource records
163 using the -r command.
164 -H Hash a known_hosts file. This replaces all hostnames and ad‐
166 dresses with hashed representations within the specified file;
167 the original content is moved to a file with a .old suffix.
168 These hashes may be used normally by ssh and sshd, but they do
169 not reveal identifying information should the file's contents be
170 disclosed. This option will not modify existing hashed hostnames
171 and is therefore safe to use on files that mix hashed and non-
172 hashed names.
173 -h When signing a key, create a host certificate instead of a user
175 certificate. Please see the CERTIFICATES section for details.
176 -I certificate_identity
178 Specify the key identity when signing a public key. Please see
179 the CERTIFICATES section for details.
180 -i This option will read an unencrypted private (or public) key file
182 in the format specified by the -m option and print an OpenSSH
183 compatible private (or public) key to stdout. This option allows
184 importing keys from other software, including several commercial
185 SSH implementations. The default import format is “RFC4716”.
186 -K Download resident keys from a FIDO authenticator. Public and
188 private key files will be written to the current directory for
189 each downloaded key. If multiple FIDO authenticators are at‐
190 tached, keys will be downloaded from the first touched authenti‐
191 cator.
192 -k Generate a KRL file. In this mode, ssh-keygen will generate a
194 KRL file at the location specified via the -f flag that revokes
195 every key or certificate presented on the command line.
196 Keys/certificates to be revoked may be specified by public key
197 file or using the format described in the KEY REVOCATION LISTS
198 section.
199 -L Prints the contents of one or more certificates.
201 -l Show fingerprint of specified public key file. For RSA and DSA
203 keys ssh-keygen tries to find the matching public key file and
204 prints its fingerprint. If combined with -v, a visual ASCII art
205 representation of the key is supplied with the fingerprint.
206 -M generate
208 Generate candidate Diffie-Hellman Group Exchange (DH-GEX) parame‐
209 ters for eventual use by the ‘diffie-hellman-group-exchange-*’
210 key exchange methods. The numbers generated by this operation
211 must be further screened before use. See the MODULI GENERATION
212 section for more information.
213 -M screen
215 Screen candidate parameters for Diffie-Hellman Group Exchange.
216 This will accept a list of candidate numbers and test that they
217 are safe (Sophie Germain) primes with acceptable group genera‐
218 tors. The results of this operation may be added to the
219 /etc/ssh/moduli file. See the MODULI GENERATION section for more
220 information.
221 -m key_format
223 Specify a key format for key generation, the -i (import), -e (ex‐
224 port) conversion options, and the -p change passphrase operation.
225 The latter may be used to convert between OpenSSH private key and
226 PEM private key formats. The supported key formats are:
227 “RFC4716” (RFC 4716/SSH2 public or private key), “PKCS8” (PKCS8
228 public or private key) or “PEM” (PEM public key). By default
229 OpenSSH will write newly-generated private keys in its own for‐
230 mat, but when converting public keys for export the default for‐
231 mat is “RFC4716”. Setting a format of “PEM” when generating or
232 updating a supported private key type will cause the key to be
233 stored in the legacy PEM private key format.
234 -N new_passphrase
236 Provides the new passphrase.
237 -n principals
239 Specify one or more principals (user or host names) to be in‐
240 cluded in a certificate when signing a key. Multiple principals
241 may be specified, separated by commas. Please see the
242 CERTIFICATES section for details.
243 -O option
245 Specify a key/value option. These are specific to the operation
246 that ssh-keygen has been requested to perform.
247 When signing certificates, one of the options listed in the
249 CERTIFICATES section may be specified here.
250 When performing moduli generation or screening, one of the op‐
252 tions listed in the MODULI GENERATION section may be specified.
253 When generating a key that will be hosted on a FIDO authentica‐
255 tor, this flag may be used to specify key-specific options.
256 Those supported at present are:
257 application
259 Override the default FIDO application/origin string of
260 “ssh:”. This may be useful when generating host or do‐
261 main-specific resident keys. The specified application
262 string must begin with “ssh:”.
263 challenge=path
265 Specifies a path to a challenge string that will be
266 passed to the FIDO token during key generation. The
267 challenge string may be used as part of an out-of-band
268 protocol for key enrollment (a random challenge is used
269 by default).
270 device Explicitly specify a fido(4) device to use, rather than
272 letting the token middleware select one.
273 no-touch-required
275 Indicate that the generated private key should not re‐
276 quire touch events (user presence) when making signa‐
277 tures. Note that sshd(8) will refuse such signatures by
278 default, unless overridden via an authorized_keys option.
279 resident
281 Indicate that the key should be stored on the FIDO au‐
282 thenticator itself. Resident keys may be supported on
283 FIDO2 tokens and typically require that a PIN be set on
284 the token prior to generation. Resident keys may be
285 loaded off the token using ssh-add(1).
286 user A username to be associated with a resident key, overrid‐
288 ing the empty default username. Specifying a username
289 may be useful when generating multiple resident keys for
290 the same application name.
291 verify-required
293 Indicate that this private key should require user veri‐
294 fication for each signature. Not all FIDO tokens support
295 this option. Currently PIN authentication is the only
296 supported verification method, but other methods may be
297 supported in the future.
298 write-attestation=path
300 May be used at key generation time to record the attesta‐
301 tion data returned from FIDO tokens during key genera‐
302 tion. Please note that this information is potentially
303 sensitive. By default, this information is discarded.
304 When performing signature-related options using the -Y flag, the
306 following options are accepted:
307 print-pubkey
309 Print the full public key to standard output after signa‐
310 ture verification.
311 verify-time=timestamp
313 Specifies a time to use when validating signatures in‐
314 stead of the current time. The time may be specified as
315 a date in YYYYMMDD format or a time in YYYYMMDDHHMM[SS]
316 format.
317 The -O option may be specified multiple times.
319 -P passphrase
321 Provides the (old) passphrase.
322 -p Requests changing the passphrase of a private key file instead of
324 creating a new private key. The program will prompt for the file
325 containing the private key, for the old passphrase, and twice for
326 the new passphrase.
327 -Q Test whether keys have been revoked in a KRL. If the -l option
329 is also specified then the contents of the KRL will be printed.
330 -q Silence ssh-keygen.
332 -R hostname | [hostname]:port
334 Removes all keys belonging to the specified hostname (with op‐
335 tional port number) from a known_hosts file. This option is use‐
336 ful to delete hashed hosts (see the -H option above).
337 -r hostname
339 Print the SSHFP fingerprint resource record named hostname for
340 the specified public key file.
341 -s ca_key
343 Certify (sign) a public key using the specified CA key. Please
344 see the CERTIFICATES section for details.
345 When generating a KRL, -s specifies a path to a CA public key
347 file used to revoke certificates directly by key ID or serial
348 number. See the KEY REVOCATION LISTS section for details.
349 -t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa
351 Specifies the type of key to create. The possible values are
352 “dsa”, “ecdsa”, “ecdsa-sk”, “ed25519”, “ed25519-sk”, or “rsa”.
353 This flag may also be used to specify the desired signature type
355 when signing certificates using an RSA CA key. The available RSA
356 signature variants are “ssh-rsa” (SHA1 signatures, not recom‐
357 mended), “rsa-sha2-256”, and “rsa-sha2-512” (the default).
358 -U When used in combination with -s, this option indicates that a CA
360 key resides in a ssh-agent(1). See the CERTIFICATES section for
361 more information.
362 -u Update a KRL. When specified with -k, keys listed via the com‐
364 mand line are added to the existing KRL rather than a new KRL be‐
365 ing created.
366 -V validity_interval
368 Specify a validity interval when signing a certificate. A valid‐
369 ity interval may consist of a single time, indicating that the
370 certificate is valid beginning now and expiring at that time, or
371 may consist of two times separated by a colon to indicate an ex‐
372 plicit time interval.
373 The start time may be specified as the string “always” to indi‐
375 cate the certificate has no specified start time, a date in
376 YYYYMMDD format, a time in YYYYMMDDHHMM[SS] format, a relative
377 time (to the current time) consisting of a minus sign followed by
378 an interval in the format described in the TIME FORMATS section
379 of sshd_config(5).
380 The end time may be specified as a YYYYMMDD date, a YYYYMMD‐
382 DHHMM[SS] time, a relative time starting with a plus character or
383 the string “forever” to indicate that the certificate has no ex‐
384 piry date.
385 For example: “+52w1d” (valid from now to 52 weeks and one day
387 from now), “-4w:+4w” (valid from four weeks ago to four weeks
388 from now), “20100101123000:20110101123000” (valid from 12:30 PM,
389 January 1st, 2010 to 12:30 PM, January 1st, 2011), “-1d:20110101”
390 (valid from yesterday to midnight, January 1st, 2011),
391 “-1m:forever” (valid from one minute ago and never expiring).
392 -v Verbose mode. Causes ssh-keygen to print debugging messages
394 about its progress. This is helpful for debugging moduli genera‐
395 tion. Multiple -v options increase the verbosity. The maximum
396 is 3.
397 -w provider
399 Specifies a path to a library that will be used when creating
400 FIDO authenticator-hosted keys, overriding the default of using
401 the internal USB HID support.
402 -Y find-principals
404 Find the principal(s) associated with the public key of a signa‐
405 ture, provided using the -s flag in an authorized signers file
406 provided using the -f flag. The format of the allowed signers
407 file is documented in the ALLOWED SIGNERS section below. If one
408 or more matching principals are found, they are returned on stan‐
409 dard output.
410 -Y check-novalidate
412 Checks that a signature generated using ssh-keygen -Y sign has a
413 valid structure. This does not validate if a signature comes
414 from an authorized signer. When testing a signature, ssh-keygen
415 accepts a message on standard input and a signature namespace us‐
416 ing -n. A file containing the corresponding signature must also
417 be supplied using the -s flag. Successful testing of the signa‐
418 ture is signalled by ssh-keygen returning a zero exit status.
419 -Y sign
421 Cryptographically sign a file or some data using a SSH key. When
422 signing, ssh-keygen accepts zero or more files to sign on the
423 command-line - if no files are specified then ssh-keygen will
424 sign data presented on standard input. Signatures are written to
425 the path of the input file with “.sig” appended, or to standard
426 output if the message to be signed was read from standard input.
427 The key used for signing is specified using the -f option and may
429 refer to either a private key, or a public key with the private
430 half available via ssh-agent(1). An additional signature name‐
431 space, used to prevent signature confusion across different do‐
432 mains of use (e.g. file signing vs email signing) must be pro‐
433 vided via the -n flag. Namespaces are arbitrary strings, and may
434 include: “file” for file signing, “email” for email signing. For
435 custom uses, it is recommended to use names following a NAME‐
436 SPACE@YOUR.DOMAIN pattern to generate unambiguous namespaces.
437 -Y verify
439 Request to verify a signature generated using ssh-keygen -Y sign
440 as described above. When verifying a signature, ssh-keygen ac‐
441 cepts a message on standard input and a signature namespace using
442 -n. A file containing the corresponding signature must also be
443 supplied using the -s flag, along with the identity of the signer
444 using -I and a list of allowed signers via the -f flag. The for‐
445 mat of the allowed signers file is documented in the ALLOWED
446 SIGNERS section below. A file containing revoked keys can be
447 passed using the -r flag. The revocation file may be a KRL or a
448 one-per-line list of public keys. Successful verification by an
449 authorized signer is signalled by ssh-keygen returning a zero
450 exit status.
451 -y This option will read a private OpenSSH format file and print an
453 OpenSSH public key to stdout.
454 -Z cipher
456 Specifies the cipher to use for encryption when writing an
457 OpenSSH-format private key file. The list of available ciphers
458 may be obtained using "ssh -Q cipher". The default is
459 “aes256-ctr”.
460 -z serial_number
462 Specifies a serial number to be embedded in the certificate to
463 distinguish this certificate from others from the same CA. If
464 the serial_number is prefixed with a ‘+’ character, then the se‐
465 rial number will be incremented for each certificate signed on a
466 single command-line. The default serial number is zero.
467 When generating a KRL, the -z flag is used to specify a KRL ver‐
469 sion number.
470
472 ssh-keygen may be used to generate groups for the Diffie-Hellman Group
473 Exchange (DH-GEX) protocol. Generating these groups is a two-step
474 process: first, candidate primes are generated using a fast, but memory
475 intensive process. These candidate primes are then tested for suitabil‐
476 ity (a CPU-intensive process).
477 Generation of primes is performed using the -M generate option. The de‐
479 sired length of the primes may be specified by the -O bits option. For
480 example:
481 # ssh-keygen -M generate -O bits=2048 moduli-2048.candidates
483 By default, the search for primes begins at a random point in the desired
485 length range. This may be overridden using the -O start option, which
486 specifies a different start point (in hex).
487 Once a set of candidates have been generated, they must be screened for
489 suitability. This may be performed using the -M screen option. In this
490 mode ssh-keygen will read candidates from standard input (or a file spec‐
491 ified using the -f option). For example:
492 # ssh-keygen -M screen -f moduli-2048.candidates moduli-2048
494 By default, each candidate will be subjected to 100 primality tests.
496 This may be overridden using the -O prime-tests option. The DH generator
497 value will be chosen automatically for the prime under consideration. If
498 a specific generator is desired, it may be requested using the -O
499 generator option. Valid generator values are 2, 3, and 5.
500 Screened DH groups may be installed in /etc/ssh/moduli. It is important
502 that this file contains moduli of a range of bit lengths.
503 A number of options are available for moduli generation and screening via
505 the -O flag:
506 lines=number
508 Exit after screening the specified number of lines while perform‐
509 ing DH candidate screening.
510 start-line=line-number
512 Start screening at the specified line number while performing DH
513 candidate screening.
514 checkpoint=filename
516 Write the last line processed to the specified file while per‐
517 forming DH candidate screening. This will be used to skip lines
518 in the input file that have already been processed if the job is
519 restarted.
520 memory=mbytes
522 Specify the amount of memory to use (in megabytes) when generat‐
523 ing candidate moduli for DH-GEX.
524 start=hex-value
526 Specify start point (in hex) when generating candidate moduli for
527 DH-GEX.
528 generator=value
530 Specify desired generator (in decimal) when testing candidate
531 moduli for DH-GEX.
532
534 ssh-keygen supports signing of keys to produce certificates that may be
535 used for user or host authentication. Certificates consist of a public
536 key, some identity information, zero or more principal (user or host)
537 names and a set of options that are signed by a Certification Authority
538 (CA) key. Clients or servers may then trust only the CA key and verify
539 its signature on a certificate rather than trusting many user/host keys.
540 Note that OpenSSH certificates are a different, and much simpler, format
541 to the X.509 certificates used in ssl(8).
542 ssh-keygen supports two types of certificates: user and host. User cer‐
544 tificates authenticate users to servers, whereas host certificates au‐
545 thenticate server hosts to users. To generate a user certificate:
546 $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
548 The resultant certificate will be placed in /path/to/user_key-cert.pub.
550 A host certificate requires the -h option:
551 $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
553 The host certificate will be output to /path/to/host_key-cert.pub.
555 It is possible to sign using a CA key stored in a PKCS#11 token by pro‐
557 viding the token library using -D and identifying the CA key by providing
558 its public half as an argument to -s:
559 $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub
561 Similarly, it is possible for the CA key to be hosted in a ssh-agent(1).
563 This is indicated by the -U flag and, again, the CA key must be identi‐
564 fied by its public half.
565 $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub
567 In all cases, key_id is a "key identifier" that is logged by the server
569 when the certificate is used for authentication.
570 Certificates may be limited to be valid for a set of principal
572 (user/host) names. By default, generated certificates are valid for all
573 users or hosts. To generate a certificate for a specified set of princi‐
574 pals:
575 $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
577 $ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub
578 Additional limitations on the validity and use of user certificates may
580 be specified through certificate options. A certificate option may dis‐
581 able features of the SSH session, may be valid only when presented from
582 particular source addresses or may force the use of a specific command.
583 The options that are valid for user certificates are:
585 clear Clear all enabled permissions. This is useful for clearing the
587 default set of permissions so permissions may be added individu‐
588 ally.
589 critical:name[=contents]
591 extension:name[=contents]
592 Includes an arbitrary certificate critical option or extension.
593 The specified name should include a domain suffix, e.g.
594 “name@example.com”. If contents is specified then it is included
595 as the contents of the extension/option encoded as a string, oth‐
596 erwise the extension/option is created with no contents (usually
597 indicating a flag). Extensions may be ignored by a client or
598 server that does not recognise them, whereas unknown critical op‐
599 tions will cause the certificate to be refused.
600 force-command=command
602 Forces the execution of command instead of any shell or command
603 specified by the user when the certificate is used for authenti‐
604 cation.
605 no-agent-forwarding
607 Disable ssh-agent(1) forwarding (permitted by default).
608 no-port-forwarding
610 Disable port forwarding (permitted by default).
611 no-pty Disable PTY allocation (permitted by default).
613 no-user-rc
615 Disable execution of ~/.ssh/rc by sshd(8) (permitted by default).
616 no-x11-forwarding
618 Disable X11 forwarding (permitted by default).
619 permit-agent-forwarding
621 Allows ssh-agent(1) forwarding.
622 permit-port-forwarding
624 Allows port forwarding.
625 permit-pty
627 Allows PTY allocation.
628 permit-user-rc
630 Allows execution of ~/.ssh/rc by sshd(8).
631 permit-X11-forwarding
633 Allows X11 forwarding.
634 no-touch-required
636 Do not require signatures made using this key include demonstra‐
637 tion of user presence (e.g. by having the user touch the authen‐
638 ticator). This option only makes sense for the FIDO authentica‐
639 tor algorithms ecdsa-sk and ed25519-sk.
640 source-address=address_list
642 Restrict the source addresses from which the certificate is con‐
643 sidered valid. The address_list is a comma-separated list of one
644 or more address/netmask pairs in CIDR format.
645 verify-required
647 Require signatures made using this key indicate that the user was
648 first verified. This option only makes sense for the FIDO au‐
649 thenticator algorithms ecdsa-sk and ed25519-sk. Currently PIN
650 authentication is the only supported verification method, but
651 other methods may be supported in the future.
652 At present, no standard options are valid for host keys.
654 Finally, certificates may be defined with a validity lifetime. The -V
656 option allows specification of certificate start and end times. A cer‐
657 tificate that is presented at a time outside this range will not be con‐
658 sidered valid. By default, certificates are valid from the UNIX Epoch to
659 the distant future.
660 For certificates to be used for user or host authentication, the CA pub‐
662 lic key must be trusted by sshd(8) or ssh(1). Please refer to those man‐
663 ual pages for details.
664
666 ssh-keygen is able to manage OpenSSH format Key Revocation Lists (KRLs).
667 These binary files specify keys or certificates to be revoked using a
668 compact format, taking as little as one bit per certificate if they are
669 being revoked by serial number.
670 KRLs may be generated using the -k flag. This option reads one or more
672 files from the command line and generates a new KRL. The files may ei‐
673 ther contain a KRL specification (see below) or public keys, listed one
674 per line. Plain public keys are revoked by listing their hash or con‐
675 tents in the KRL and certificates revoked by serial number or key ID (if
676 the serial is zero or not available).
677 Revoking keys using a KRL specification offers explicit control over the
679 types of record used to revoke keys and may be used to directly revoke
680 certificates by serial number or key ID without having the complete orig‐
681 inal certificate on hand. A KRL specification consists of lines contain‐
682 ing one of the following directives followed by a colon and some direc‐
683 tive-specific information.
684 serial: serial_number[-serial_number]
686 Revokes a certificate with the specified serial number. Serial
687 numbers are 64-bit values, not including zero and may be ex‐
688 pressed in decimal, hex or octal. If two serial numbers are
689 specified separated by a hyphen, then the range of serial numbers
690 including and between each is revoked. The CA key must have been
691 specified on the ssh-keygen command line using the -s option.
692 id: key_id
694 Revokes a certificate with the specified key ID string. The CA
695 key must have been specified on the ssh-keygen command line using
696 the -s option.
697 key: public_key
699 Revokes the specified key. If a certificate is listed, then it
700 is revoked as a plain public key.
701 sha1: public_key
703 Revokes the specified key by including its SHA1 hash in the KRL.
704 sha256: public_key
706 Revokes the specified key by including its SHA256 hash in the
707 KRL. KRLs that revoke keys by SHA256 hash are not supported by
708 OpenSSH versions prior to 7.9.
709 hash: fingerprint
711 Revokes a key using a fingerprint hash, as obtained from a
712 sshd(8) authentication log message or the ssh-keygen -l flag.
713 Only SHA256 fingerprints are supported here and resultant KRLs
714 are not supported by OpenSSH versions prior to 7.9.
715 KRLs may be updated using the -u flag in addition to -k. When this op‐
717 tion is specified, keys listed via the command line are merged into the
718 KRL, adding to those already there.
719 It is also possible, given a KRL, to test whether it revokes a particular
721 key (or keys). The -Q flag will query an existing KRL, testing each key
722 specified on the command line. If any key listed on the command line has
723 been revoked (or an error encountered) then ssh-keygen will exit with a
724 non-zero exit status. A zero exit status will only be returned if no key
725 was revoked.
726
728 When verifying signatures, ssh-keygen uses a simple list of identities
729 and keys to determine whether a signature comes from an authorized
730 source. This "allowed signers" file uses a format patterned after the
731 AUTHORIZED_KEYS FILE FORMAT described in sshd(8). Each line of the file
732 contains the following space-separated fields: principals, options, key‐
733 type, base64-encoded key. Empty lines and lines starting with a ‘#’ are
734 ignored as comments.
735 The principals field is a pattern-list (see PATTERNS in ssh_config(5))
737 consisting of one or more comma-separated USER@DOMAIN identity patterns
738 that are accepted for signing. When verifying, the identity presented
739 via the -I option must match a principals pattern in order for the corre‐
740 sponding key to be considered acceptable for verification.
741 The options (if present) consist of comma-separated option specifica‐
743 tions. No spaces are permitted, except within double quotes. The fol‐
744 lowing option specifications are supported (note that option keywords are
745 case-insensitive):
746 cert-authority
748 Indicates that this key is accepted as a certificate authority
749 (CA) and that certificates signed by this CA may be accepted for
750 verification.
751 namespaces=namespace-list
753 Specifies a pattern-list of namespaces that are accepted for this
754 key. If this option is present, the signature namespace embedded
755 in the signature object and presented on the verification com‐
756 mand-line must match the specified list before the key will be
757 considered acceptable.
758 valid-after=timestamp
760 Indicates that the key is valid for use at or after the specified
761 timestamp, which may be a date in YYYYMMDD format or a time in
762 YYYYMMDDHHMM[SS] format.
763 valid-before=timestamp
765 Indicates that the key is valid for use at or before the speci‐
766 fied timestamp.
767 When verifying signatures made by certificates, the expected principal
769 name must match both the principals pattern in the allowed signers file
770 and the principals embedded in the certificate itself.
771 An example allowed signers file:
773 # Comments allowed at start of line
775 user1@example.com,user2@example.com ssh-rsa AAAAX1...
776 # A certificate authority, trusted for all principals in a domain.
777 *@example.com cert-authority ssh-ed25519 AAAB4...
778 # A key that is accepted only for file signing.
779 user2@example.com namespaces="file" ssh-ed25519 AAA41...
780
782 SSH_SK_PROVIDER
783 Specifies a path to a library that will be used when loading any
784 FIDO authenticator-hosted keys, overriding the default of using
785 the built-in USB HID support.
786
788 ~/.ssh/id_dsa
789 ~/.ssh/id_ecdsa
790 ~/.ssh/id_ecdsa_sk
791 ~/.ssh/id_ed25519
792 ~/.ssh/id_ed25519_sk
793 ~/.ssh/id_rsa
794 Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, au‐
795 thenticator-hosted Ed25519 or RSA authentication identity of the
796 user. This file should not be readable by anyone but the user.
797 It is possible to specify a passphrase when generating the key;
798 that passphrase will be used to encrypt the private part of this
799 file using 128-bit AES. This file is not automatically accessed
800 by ssh-keygen but it is offered as the default file for the pri‐
801 vate key. ssh(1) will read this file when a login attempt is
802 made.
803 ~/.ssh/id_dsa.pub
805 ~/.ssh/id_ecdsa.pub
806 ~/.ssh/id_ecdsa_sk.pub
807 ~/.ssh/id_ed25519.pub
808 ~/.ssh/id_ed25519_sk.pub
809 ~/.ssh/id_rsa.pub
810 Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, au‐
811 thenticator-hosted Ed25519 or RSA public key for authentication.
812 The contents of this file should be added to
813 ~/.ssh/authorized_keys on all machines where the user wishes to
814 log in using public key authentication. There is no need to keep
815 the contents of this file secret.
816 /etc/ssh/moduli
818 Contains Diffie-Hellman groups used for DH-GEX. The file format
819 is described in moduli(5).
820
822 ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
823 The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006.
825
827 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
828 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
829 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
830 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
831 versions 1.5 and 2.0.
832BSD August 11, 2021 BSD