1SSH-KEYGEN(1) BSD General Commands Manual SSH-KEYGEN(1)
2
4 ssh-keygen — OpenSSH authentication key utility
5
7 ssh-keygen [-q] [-b bits] [-C comment] [-f output_keyfile] [-m format]
8 [-t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa]
9 [-N new_passphrase] [-O option] [-w provider]
10 ssh-keygen -p [-f keyfile] [-m format] [-N new_passphrase]
11 [-P old_passphrase]
12 ssh-keygen -i [-f input_keyfile] [-m key_format]
13 ssh-keygen -e [-f input_keyfile] [-m key_format]
14 ssh-keygen -y [-f input_keyfile]
15 ssh-keygen -c [-C comment] [-f keyfile] [-P passphrase]
16 ssh-keygen -l [-v] [-E fingerprint_hash] [-f input_keyfile]
17 ssh-keygen -B [-f input_keyfile]
18 ssh-keygen -D pkcs11
19 ssh-keygen -F hostname [-lv] [-f known_hosts_file]
20 ssh-keygen -H [-f known_hosts_file]
21 ssh-keygen -K [-w provider]
22 ssh-keygen -R hostname [-f known_hosts_file]
23 ssh-keygen -r hostname [-g] [-f input_keyfile]
24 ssh-keygen -M generate [-O option] output_file
25 ssh-keygen -M screen [-f input_file] [-O option] output_file
26 ssh-keygen -I certificate_identity -s ca_key [-hU] [-D pkcs11_provider]
27 [-n principals] [-O option] [-V validity_interval]
28 [-z serial_number] file ...
29 ssh-keygen -L [-f input_keyfile]
30 ssh-keygen -A [-f prefix_path]
31 ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number]
32 file ...
33 ssh-keygen -Q -f krl_file file ...
34 ssh-keygen -Y find-principals -s signature_file -f allowed_signers_file
35 ssh-keygen -Y check-novalidate -n namespace -s signature_file
36 ssh-keygen -Y sign -f key_file -n namespace file ...
37 ssh-keygen -Y verify -f allowed_signers_file -I signer_identity -n
38 namespace -s signature_file [-r revocation_file]
39
41 ssh-keygen generates, manages and converts authentication keys for
42 ssh(1). ssh-keygen can create keys for use by SSH protocol version 2.
43 The type of key to be generated is specified with the -t option. If
45 invoked without any arguments, ssh-keygen will generate an RSA key.
46 ssh-keygen is also used to generate groups for use in Diffie-Hellman
48 group exchange (DH-GEX). See the MODULI GENERATION section for details.
49 Finally, ssh-keygen can be used to generate and update Key Revocation
51 Lists, and to test whether given keys have been revoked by one. See the
52 KEY REVOCATION LISTS section for details.
53 Normally each user wishing to use SSH with public key authentication runs
55 this once to create the authentication key in ~/.ssh/id_dsa,
56 ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
57 ~/.ssh/id_ed25519_sk or ~/.ssh/id_rsa. Additionally, the system adminis‐
58 trator may use this to generate host keys, as seen in /etc/rc.
59 Normally this program generates the key and asks for a file in which to
61 store the private key. The public key is stored in a file with the same
62 name but “.pub” appended. The program also asks for a passphrase. The
63 passphrase may be empty to indicate no passphrase (host keys must have an
64 empty passphrase), or it may be a string of arbitrary length. A
65 passphrase is similar to a password, except it can be a phrase with a
66 series of words, punctuation, numbers, whitespace, or any string of char‐
67 acters you want. Good passphrases are 10-30 characters long, are not
68 simple sentences or otherwise easily guessable (English prose has only
69 1-2 bits of entropy per character, and provides very bad passphrases),
70 and contain a mix of upper and lowercase letters, numbers, and non-
71 alphanumeric characters. The passphrase can be changed later by using
72 the -p option.
73 There is no way to recover a lost passphrase. If the passphrase is lost
75 or forgotten, a new key must be generated and the corresponding public
76 key copied to other machines.
77 ssh-keygen will by default write keys in an OpenSSH-specific format.
79 This format is preferred as it offers better protection for keys at rest
80 as well as allowing storage of key comments within the private key file
81 itself. The key comment may be useful to help identify the key. The
82 comment is initialized to “user@host” when the key is created, but can be
83 changed using the -c option.
84 It is still possible for ssh-keygen to write the previously-used PEM for‐
86 mat private keys using the -m flag. This may be used when generating new
87 keys, and existing new-format keys may be converted using this option in
88 conjunction with the -p (change passphrase) flag.
89 After a key is generated, instructions below detail where the keys should
91 be placed to be activated.
92 The options are as follows:
94 -A For each of the key types (rsa, dsa, ecdsa and ed25519) for which
96 host keys do not exist, generate the host keys with the default
97 key file path, an empty passphrase, default bits for the key
98 type, and default comment. If -f has also been specified, its
99 argument is used as a prefix to the default path for the result‐
100 ing host key files. This is used by /etc/rc to generate new host
101 keys.
102 -a rounds
104 When saving a private key, this option specifies the number of
105 KDF (key derivation function) rounds used. Higher numbers result
106 in slower passphrase verification and increased resistance to
107 brute-force password cracking (should the keys be stolen).
108 -B Show the bubblebabble digest of specified private or public key
110 file.
111 -b bits
113 Specifies the number of bits in the key to create. For RSA keys,
114 the minimum size is 1024 bits and the default is 3072 bits. Gen‐
115 erally, 3072 bits is considered sufficient. DSA keys must be
116 exactly 1024 bits as specified by FIPS 186-2. For ECDSA keys,
117 the -b flag determines the key length by selecting from one of
118 three elliptic curve sizes: 256, 384 or 521 bits. Attempting to
119 use bit lengths other than these three values for ECDSA keys will
120 fail. ECDSA-SK, Ed25519 and Ed25519-SK keys have a fixed length
121 and the -b flag will be ignored.
122 -C comment
124 Provides a new comment.
125 -c Requests changing the comment in the private and public key
127 files. The program will prompt for the file containing the pri‐
128 vate keys, for the passphrase if the key has one, and for the new
129 comment.
130 -D pkcs11
132 Download the public keys provided by the PKCS#11 shared library
133 pkcs11. When used in combination with -s, this option indicates
134 that a CA key resides in a PKCS#11 token (see the CERTIFICATES
135 section for details).
136 -E fingerprint_hash
138 Specifies the hash algorithm used when displaying key finger‐
139 prints. Valid options are: “md5” and “sha256”. The default is
140 “sha256”.
141 -e This option will read a private or public OpenSSH key file and
143 print to stdout a public key in one of the formats specified by
144 the -m option. The default export format is “RFC4716”. This
145 option allows exporting OpenSSH keys for use by other programs,
146 including several commercial SSH implementations.
147 -F hostname | [hostname]:port
149 Search for the specified hostname (with optional port number) in
150 a known_hosts file, listing any occurrences found. This option
151 is useful to find hashed host names or addresses and may also be
152 used in conjunction with the -H option to print found keys in a
153 hashed format.
154 -f filename
156 Specifies the filename of the key file.
157 -g Use generic DNS format when printing fingerprint resource records
159 using the -r command.
160 -H Hash a known_hosts file. This replaces all hostnames and
162 addresses with hashed representations within the specified file;
163 the original content is moved to a file with a .old suffix.
164 These hashes may be used normally by ssh and sshd, but they do
165 not reveal identifying information should the file's contents be
166 disclosed. This option will not modify existing hashed hostnames
167 and is therefore safe to use on files that mix hashed and non-
168 hashed names.
169 -h When signing a key, create a host certificate instead of a user
171 certificate. Please see the CERTIFICATES section for details.
172 -I certificate_identity
174 Specify the key identity when signing a public key. Please see
175 the CERTIFICATES section for details.
176 -i This option will read an unencrypted private (or public) key file
178 in the format specified by the -m option and print an OpenSSH
179 compatible private (or public) key to stdout. This option allows
180 importing keys from other software, including several commercial
181 SSH implementations. The default import format is “RFC4716”.
182 -K Download resident keys from a FIDO authenticator. Public and
184 private key files will be written to the current directory for
185 each downloaded key.
186 -k Generate a KRL file. In this mode, ssh-keygen will generate a
188 KRL file at the location specified via the -f flag that revokes
189 every key or certificate presented on the command line.
190 Keys/certificates to be revoked may be specified by public key
191 file or using the format described in the KEY REVOCATION LISTS
192 section.
193 -L Prints the contents of one or more certificates.
195 -l Show fingerprint of specified public key file. For RSA and DSA
197 keys ssh-keygen tries to find the matching public key file and
198 prints its fingerprint. If combined with -v, a visual ASCII art
199 representation of the key is supplied with the fingerprint.
200 -M generate
202 Generate candidate Diffie-Hellman Group Exchange (DH-GEX) parame‐
203 ters for eventual use by the ‘diffie-hellman-group-exchange-*’
204 key exchange methods. The numbers generated by this operation
205 must be further screened before use. See the MODULI GENERATION
206 section for more information.
207 -M screen
209 Screen candidate parameters for Diffie-Hellman Group Exchange.
210 This will accept a list of candidate numbers and test that they
211 are safe (Sophie Germain) primes with acceptable group genera‐
212 tors. The results of this operation may be added to the
213 /etc/ssh/moduli file. See the MODULI GENERATION section for more
214 information.
215 -m key_format
217 Specify a key format for key generation, the -i (import), -e
218 (export) conversion options, and the -p change passphrase opera‐
219 tion. The latter may be used to convert between OpenSSH private
220 key and PEM private key formats. The supported key formats are:
221 “RFC4716” (RFC 4716/SSH2 public or private key), “PKCS8” (PKCS8
222 public or private key) or “PEM” (PEM public key). By default
223 OpenSSH will write newly-generated private keys in its own for‐
224 mat, but when converting public keys for export the default for‐
225 mat is “RFC4716”. Setting a format of “PEM” when generating or
226 updating a supported private key type will cause the key to be
227 stored in the legacy PEM private key format.
228 -N new_passphrase
230 Provides the new passphrase.
231 -n principals
233 Specify one or more principals (user or host names) to be
234 included in a certificate when signing a key. Multiple princi‐
235 pals may be specified, separated by commas. Please see the
236 CERTIFICATES section for details.
237 -O option
239 Specify a key/value option. These are specific to the operation
240 that ssh-keygen has been requested to perform.
241 When signing certificates, one of the options listed in the
243 CERTIFICATES section may be specified here.
244 When performing moduli generation or screening, one of the
246 options listed in the MODULI GENERATION section may be specified.
247 When generating a key that will be hosted on a FIDO authentica‐
249 tor, this flag may be used to specify key-specific options.
250 Those supported at present are:
251 application
253 Override the default FIDO application/origin string of
254 “ssh:”. This may be useful when generating host or
255 domain-specific resident keys. The specified application
256 string must begin with “ssh:”.
257 challenge=path
259 Specifies a path to a challenge string that will be
260 passed to the FIDO token during key generation. The
261 challenge string may be used as part of an out-of-band
262 protocol for key enrollment (a random challenge is used
263 by default).
264 device Explicitly specify a fido(4) device to use, rather than
266 letting the token middleware select one.
267 no-touch-required
269 Indicate that the generated private key should not
270 require touch events (user presence) when making signa‐
271 tures. Note that sshd(8) will refuse such signatures by
272 default, unless overridden via an authorized_keys option.
273 resident
275 Indicate that the key should be stored on the FIDO
276 authenticator itself. Resident keys may be supported on
277 FIDO2 tokens and typically require that a PIN be set on
278 the token prior to generation. Resident keys may be
279 loaded off the token using ssh-add(1).
280 user A username to be associated with a resident key, overrid‐
282 ing the empty default username. Specifying a username
283 may be useful when generating multiple resident keys for
284 the same application name.
285 write-attestation=path
287 May be used at key generation time to record the attesta‐
288 tion certificate returned from FIDO tokens during key
289 generation. By default this information is discarded.
290 The -O option may be specified multiple times.
292 -P passphrase
294 Provides the (old) passphrase.
295 -p Requests changing the passphrase of a private key file instead of
297 creating a new private key. The program will prompt for the file
298 containing the private key, for the old passphrase, and twice for
299 the new passphrase.
300 -Q Test whether keys have been revoked in a KRL.
302 -q Silence ssh-keygen.
304 -R hostname | [hostname]:port
306 Removes all keys belonging to the specified hostname (with
307 optional port number) from a known_hosts file. This option is
308 useful to delete hashed hosts (see the -H option above).
309 -r hostname
311 Print the SSHFP fingerprint resource record named hostname for
312 the specified public key file.
313 -s ca_key
315 Certify (sign) a public key using the specified CA key. Please
316 see the CERTIFICATES section for details.
317 When generating a KRL, -s specifies a path to a CA public key
319 file used to revoke certificates directly by key ID or serial
320 number. See the KEY REVOCATION LISTS section for details.
321 -t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa
323 Specifies the type of key to create. The possible values are
324 “dsa”, “ecdsa”, “ecdsa-sk”, “ed25519”, “ed25519-sk”, or “rsa”.
325 This flag may also be used to specify the desired signature type
327 when signing certificates using an RSA CA key. The available RSA
328 signature variants are “ssh-rsa” (SHA1 signatures, not recom‐
329 mended), “rsa-sha2-256”, and “rsa-sha2-512” (the default).
330 -U When used in combination with -s, this option indicates that a CA
332 key resides in a ssh-agent(1). See the CERTIFICATES section for
333 more information.
334 -u Update a KRL. When specified with -k, keys listed via the com‐
336 mand line are added to the existing KRL rather than a new KRL
337 being created.
338 -V validity_interval
340 Specify a validity interval when signing a certificate. A valid‐
341 ity interval may consist of a single time, indicating that the
342 certificate is valid beginning now and expiring at that time, or
343 may consist of two times separated by a colon to indicate an
344 explicit time interval.
345 The start time may be specified as the string “always” to indi‐
347 cate the certificate has no specified start time, a date in
348 YYYYMMDD format, a time in YYYYMMDDHHMM[SS] format, a relative
349 time (to the current time) consisting of a minus sign followed by
350 an interval in the format described in the TIME FORMATS section
351 of sshd_config(5).
352 The end time may be specified as a YYYYMMDD date, a YYYYMMD‐
354 DHHMM[SS] time, a relative time starting with a plus character or
355 the string “forever” to indicate that the certificate has no
356 expirty date.
357 For example: “+52w1d” (valid from now to 52 weeks and one day
359 from now), “-4w:+4w” (valid from four weeks ago to four weeks
360 from now), “20100101123000:20110101123000” (valid from 12:30 PM,
361 January 1st, 2010 to 12:30 PM, January 1st, 2011), “-1d:20110101”
362 (valid from yesterday to midnight, January 1st, 2011).
363 “-1m:forever” (valid from one minute ago and never expiring).
364 -v Verbose mode. Causes ssh-keygen to print debugging messages
366 about its progress. This is helpful for debugging moduli genera‐
367 tion. Multiple -v options increase the verbosity. The maximum
368 is 3.
369 -w provider
371 Specifies a path to a library that will be used when creating
372 FIDO authenticator-hosted keys, overriding the default of using
373 the internal USB HID support.
374 -Y find-principals
376 Find the principal(s) associated with the public key of a signa‐
377 ture, provided using the -s flag in an authorized signers file
378 provided using the -f flag. The format of the allowed signers
379 file is documented in the ALLOWED SIGNERS section below. If one
380 or more matching principals are found, they are returned on stan‐
381 dard output.
382 -Y check-novalidate
384 Checks that a signature generated using ssh-keygen -Y sign has a
385 valid structure. This does not validate if a signature comes
386 from an authorized signer. When testing a signature, ssh-keygen
387 accepts a message on standard input and a signature namespace
388 using -n. A file containing the corresponding signature must
389 also be supplied using the -s flag. Successful testing of the
390 signature is signalled by ssh-keygen returning a zero exit sta‐
391 tus.
392 -Y sign
394 Cryptographically sign a file or some data using a SSH key. When
395 signing, ssh-keygen accepts zero or more files to sign on the
396 command-line - if no files are specified then ssh-keygen will
397 sign data presented on standard input. Signatures are written to
398 the path of the input file with “.sig” appended, or to standard
399 output if the message to be signed was read from standard input.
400 The key used for signing is specified using the -f option and may
402 refer to either a private key, or a public key with the private
403 half available via ssh-agent(1). An additional signature names‐
404 pace, used to prevent signature confusion across different
405 domains of use (e.g. file signing vs email signing) must be pro‐
406 vided via the -n flag. Namespaces are arbitrary strings, and may
407 include: “file” for file signing, “email” for email signing. For
408 custom uses, it is recommended to use names following a NAMES‐
409 PACE@YOUR.DOMAIN pattern to generate unambiguous namespaces.
410 -Y verify
412 Request to verify a signature generated using ssh-keygen -Y sign
413 as described above. When verifying a signature, ssh-keygen
414 accepts a message on standard input and a signature namespace
415 using -n. A file containing the corresponding signature must
416 also be supplied using the -s flag, along with the identity of
417 the signer using -I and a list of allowed signers via the -f
418 flag. The format of the allowed signers file is documented in
419 the ALLOWED SIGNERS section below. A file containing revoked
420 keys can be passed using the -r flag. The revocation file may be
421 a KRL or a one-per-line list of public keys. Successful verifi‐
422 cation by an authorized signer is signalled by ssh-keygen return‐
423 ing a zero exit status.
424 -y This option will read a private OpenSSH format file and print an
426 OpenSSH public key to stdout.
427 -z serial_number
429 Specifies a serial number to be embedded in the certificate to
430 distinguish this certificate from others from the same CA. If
431 the serial_number is prefixed with a ‘+’ character, then the
432 serial number will be incremented for each certificate signed on
433 a single command-line. The default serial number is zero.
434 When generating a KRL, the -z flag is used to specify a KRL ver‐
436 sion number.
437
439 ssh-keygen may be used to generate groups for the Diffie-Hellman Group
440 Exchange (DH-GEX) protocol. Generating these groups is a two-step
441 process: first, candidate primes are generated using a fast, but memory
442 intensive process. These candidate primes are then tested for suitabil‐
443 ity (a CPU-intensive process).
444 Generation of primes is performed using the -M generate option. The
446 desired length of the primes may be specified by the -O bits option. For
447 example:
448 # ssh-keygen -M generate -O bits=2048 moduli-2048.candidates
450 By default, the search for primes begins at a random point in the desired
452 length range. This may be overridden using the -O start option, which
453 specifies a different start point (in hex).
454 Once a set of candidates have been generated, they must be screened for
456 suitability. This may be performed using the -M screen option. In this
457 mode ssh-keygen will read candidates from standard input (or a file spec‐
458 ified using the -f option). For example:
459 # ssh-keygen -M screen -f moduli-2048.candidates moduli-2048
461 By default, each candidate will be subjected to 100 primality tests.
463 This may be overridden using the -O prime-tests option. The DH generator
464 value will be chosen automatically for the prime under consideration. If
465 a specific generator is desired, it may be requested using the -O
466 generator option. Valid generator values are 2, 3, and 5.
467 Screened DH groups may be installed in /etc/ssh/moduli. It is important
469 that this file contains moduli of a range of bit lengths and that both
470 ends of a connection share common moduli.
471 A number of options are available for moduli generation and screening via
473 the -O flag:
474 lines=number
476 Exit after screening the specified number of lines while perform‐
477 ing DH candidate screening.
478 start-line=line-number
480 Start screening at the specified line number while performing DH
481 candidate screening.
482 checkpoint=filename
484 Write the last line processed to the specified file while per‐
485 forming DH candidate screening. This will be used to skip lines
486 in the input file that have already been processed if the job is
487 restarted.
488 memory=mbytes
490 Specify the amount of memory to use (in megabytes) when generat‐
491 ing candidate moduli for DH-GEX.
492 start=hex-value
494 Specify start point (in hex) when generating candidate moduli for
495 DH-GEX.
496 generator=value
498 Specify desired generator (in decimal) when testing candidate
499 moduli for DH-GEX.
500
502 ssh-keygen supports signing of keys to produce certificates that may be
503 used for user or host authentication. Certificates consist of a public
504 key, some identity information, zero or more principal (user or host)
505 names and a set of options that are signed by a Certification Authority
506 (CA) key. Clients or servers may then trust only the CA key and verify
507 its signature on a certificate rather than trusting many user/host keys.
508 Note that OpenSSH certificates are a different, and much simpler, format
509 to the X.509 certificates used in ssl(8).
510 ssh-keygen supports two types of certificates: user and host. User cer‐
512 tificates authenticate users to servers, whereas host certificates
513 authenticate server hosts to users. To generate a user certificate:
514 $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
516 The resultant certificate will be placed in /path/to/user_key-cert.pub.
518 A host certificate requires the -h option:
519 $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
521 The host certificate will be output to /path/to/host_key-cert.pub.
523 It is possible to sign using a CA key stored in a PKCS#11 token by pro‐
525 viding the token library using -D and identifying the CA key by providing
526 its public half as an argument to -s:
527 $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub
529 Similarly, it is possible for the CA key to be hosted in a ssh-agent(1).
531 This is indicated by the -U flag and, again, the CA key must be identi‐
532 fied by its public half.
533 $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub
535 In all cases, key_id is a "key identifier" that is logged by the server
537 when the certificate is used for authentication.
538 Certificates may be limited to be valid for a set of principal
540 (user/host) names. By default, generated certificates are valid for all
541 users or hosts. To generate a certificate for a specified set of princi‐
542 pals:
543 $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
545 $ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub
546 Additional limitations on the validity and use of user certificates may
548 be specified through certificate options. A certificate option may dis‐
549 able features of the SSH session, may be valid only when presented from
550 particular source addresses or may force the use of a specific command.
551 The options that are valid for user certificates are:
553 clear Clear all enabled permissions. This is useful for clearing the
555 default set of permissions so permissions may be added individu‐
556 ally.
557 critical:name[=contents]
559 extension:name[=contents]
560 Includes an arbitrary certificate critical option or extension.
561 The specified name should include a domain suffix, e.g.
562 “name@example.com”. If contents is specified then it is included
563 as the contents of the extension/option encoded as a string, oth‐
564 erwise the extension/option is created with no contents (usually
565 indicating a flag). Extensions may be ignored by a client or
566 server that does not recognise them, whereas unknown critical
567 options will cause the certificate to be refused.
568 force-command=command
570 Forces the execution of command instead of any shell or command
571 specified by the user when the certificate is used for authenti‐
572 cation.
573 no-agent-forwarding
575 Disable ssh-agent(1) forwarding (permitted by default).
576 no-port-forwarding
578 Disable port forwarding (permitted by default).
579 no-pty Disable PTY allocation (permitted by default).
581 no-user-rc
583 Disable execution of ~/.ssh/rc by sshd(8) (permitted by default).
584 no-x11-forwarding
586 Disable X11 forwarding (permitted by default).
587 permit-agent-forwarding
589 Allows ssh-agent(1) forwarding.
590 permit-port-forwarding
592 Allows port forwarding.
593 permit-pty
595 Allows PTY allocation.
596 permit-user-rc
598 Allows execution of ~/.ssh/rc by sshd(8).
599 permit-X11-forwarding
601 Allows X11 forwarding.
602 no-touch-required
604 Do not require signatures made using this key require demonstra‐
605 tion of user presence (e.g. by having the user touch the authen‐
606 ticator). This option only makes sense for the FIDO authentica‐
607 tor algorithms ecdsa-sk and ed25519-sk.
608 source-address=address_list
610 Restrict the source addresses from which the certificate is con‐
611 sidered valid. The address_list is a comma-separated list of one
612 or more address/netmask pairs in CIDR format.
613 At present, no standard options are valid for host keys.
615 Finally, certificates may be defined with a validity lifetime. The -V
617 option allows specification of certificate start and end times. A cer‐
618 tificate that is presented at a time outside this range will not be con‐
619 sidered valid. By default, certificates are valid from UNIX Epoch to the
620 distant future.
621 For certificates to be used for user or host authentication, the CA pub‐
623 lic key must be trusted by sshd(8) or ssh(1). Please refer to those man‐
624 ual pages for details.
625
627 ssh-keygen is able to manage OpenSSH format Key Revocation Lists (KRLs).
628 These binary files specify keys or certificates to be revoked using a
629 compact format, taking as little as one bit per certificate if they are
630 being revoked by serial number.
631 KRLs may be generated using the -k flag. This option reads one or more
633 files from the command line and generates a new KRL. The files may
634 either contain a KRL specification (see below) or public keys, listed one
635 per line. Plain public keys are revoked by listing their hash or con‐
636 tents in the KRL and certificates revoked by serial number or key ID (if
637 the serial is zero or not available).
638 Revoking keys using a KRL specification offers explicit control over the
640 types of record used to revoke keys and may be used to directly revoke
641 certificates by serial number or key ID without having the complete orig‐
642 inal certificate on hand. A KRL specification consists of lines contain‐
643 ing one of the following directives followed by a colon and some direc‐
644 tive-specific information.
645 serial: serial_number[-serial_number]
647 Revokes a certificate with the specified serial number. Serial
648 numbers are 64-bit values, not including zero and may be
649 expressed in decimal, hex or octal. If two serial numbers are
650 specified separated by a hyphen, then the range of serial numbers
651 including and between each is revoked. The CA key must have been
652 specified on the ssh-keygen command line using the -s option.
653 id: key_id
655 Revokes a certificate with the specified key ID string. The CA
656 key must have been specified on the ssh-keygen command line using
657 the -s option.
658 key: public_key
660 Revokes the specified key. If a certificate is listed, then it
661 is revoked as a plain public key.
662 sha1: public_key
664 Revokes the specified key by including its SHA1 hash in the KRL.
665 sha256: public_key
667 Revokes the specified key by including its SHA256 hash in the
668 KRL. KRLs that revoke keys by SHA256 hash are not supported by
669 OpenSSH versions prior to 7.9.
670 hash: fingerprint
672 Revokes a key using a fingerprint hash, as obtained from a
673 sshd(8) authentication log message or the ssh-keygen -l flag.
674 Only SHA256 fingerprints are supported here and resultant KRLs
675 are not supported by OpenSSH versions prior to 7.9.
676 KRLs may be updated using the -u flag in addition to -k. When this
678 option is specified, keys listed via the command line are merged into the
679 KRL, adding to those already there.
680 It is also possible, given a KRL, to test whether it revokes a particular
682 key (or keys). The -Q flag will query an existing KRL, testing each key
683 specified on the command line. If any key listed on the command line has
684 been revoked (or an error encountered) then ssh-keygen will exit with a
685 non-zero exit status. A zero exit status will only be returned if no key
686 was revoked.
687
689 When verifying signatures, ssh-keygen uses a simple list of identities
690 and keys to determine whether a signature comes from an authorized
691 source. This "allowed signers" file uses a format patterned after the
692 AUTHORIZED_KEYS FILE FORMAT described in sshd(8). Each line of the file
693 contains the following space-separated fields: principals, options, key‐
694 type, base64-encoded key. Empty lines and lines starting with a ‘#’ are
695 ignored as comments.
696 The principals field is a pattern-list (See PATTERNS in ssh_config(5))
698 consisting of one or more comma-separated USER@DOMAIN identity patterns
699 that are accepted for signing. When verifying, the identity presented
700 via the -I option must match a principals pattern in order for the corre‐
701 sponding key to be considered acceptable for verification.
702 The options (if present) consist of comma-separated option specifica‐
704 tions. No spaces are permitted, except within double quotes. The fol‐
705 lowing option specifications are supported (note that option keywords are
706 case-insensitive):
707 cert-authority
709 Indicates that this key is accepted as a certificate authority
710 (CA) and that certificates signed by this CA may be accepted for
711 verification.
712 namespaces="namespace-list"
714 Specifies a pattern-list of namespaces that are accepted for this
715 key. If this option is present, the signature namespace embedded
716 in the signature object and presented on the verification com‐
717 mand-line must match the specified list before the key will be
718 considered acceptable.
719 When verifying signatures made by certificates, the expected principal
721 name must match both the principals pattern in the allowed signers file
722 and the principals embedded in the certificate itself.
723 An example allowed signers file:
725 # Comments allowed at start of line
727 user1@example.com,user2@example.com ssh-rsa AAAAX1...
728 # A certificate authority, trusted for all principals in a domain.
729 *@example.com cert-authority ssh-ed25519 AAAB4...
730 # A key that is accepted only for file signing.
731 user2@example.com namespaces="file" ssh-ed25519 AAA41...
732
734 SSH_SK_PROVIDER
735 Specifies a path to a library that will be used when loading any
736 FIDO authenticator-hosted keys, overriding the default of using
737 the built-in USB HID support.
738
740 ~/.ssh/id_dsa
741 ~/.ssh/id_ecdsa
742 ~/.ssh/id_ecdsa_sk
743 ~/.ssh/id_ed25519
744 ~/.ssh/id_ed25519_sk
745 ~/.ssh/id_rsa
746 Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519,
747 authenticator-hosted Ed25519 or RSA authentication identity of
748 the user. This file should not be readable by anyone but the
749 user. It is possible to specify a passphrase when generating the
750 key; that passphrase will be used to encrypt the private part of
751 this file using 128-bit AES. This file is not automatically
752 accessed by ssh-keygen but it is offered as the default file for
753 the private key. ssh(1) will read this file when a login attempt
754 is made.
755 ~/.ssh/id_dsa.pub
757 ~/.ssh/id_ecdsa.pub
758 ~/.ssh/id_ecdsa_sk.pub
759 ~/.ssh/id_ed25519.pub
760 ~/.ssh/id_ed25519_sk.pub
761 ~/.ssh/id_rsa.pub
762 Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519,
763 authenticator-hosted Ed25519 or RSA public key for authentica‐
764 tion. The contents of this file should be added to
765 ~/.ssh/authorized_keys on all machines where the user wishes to
766 log in using public key authentication. There is no need to keep
767 the contents of this file secret.
768 /etc/ssh/moduli
770 Contains Diffie-Hellman groups used for DH-GEX. The file format
771 is described in moduli(5).
772
774 ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
775 The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006.
777
779 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
780 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
781 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
782 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
783 versions 1.5 and 2.0.
784BSD May 10, 2020 BSD