summaryrefslogtreecommitdiff
path: root/ssh-keygen.0
diff options
context:
space:
mode:
Diffstat (limited to 'ssh-keygen.0')
-rw-r--r--ssh-keygen.0573
1 files changed, 573 insertions, 0 deletions
diff --git a/ssh-keygen.0 b/ssh-keygen.0
new file mode 100644
index 000000000..fb2c02fe7
--- /dev/null
+++ b/ssh-keygen.0
@@ -0,0 +1,573 @@
1SSH-KEYGEN(1) General Commands Manual SSH-KEYGEN(1)
2
3NAME
4 ssh-keygen M-bM-^@M-^S authentication key generation, management and conversion
5
6SYNOPSIS
7 ssh-keygen [-q] [-b bits] [-t dsa | ecdsa | ed25519 | rsa]
8 [-N new_passphrase] [-C comment] [-f output_keyfile]
9 ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile]
10 ssh-keygen -i [-m key_format] [-f input_keyfile]
11 ssh-keygen -e [-m key_format] [-f input_keyfile]
12 ssh-keygen -y [-f input_keyfile]
13 ssh-keygen -c [-P passphrase] [-C comment] [-f keyfile]
14 ssh-keygen -l [-v] [-E fingerprint_hash] [-f input_keyfile]
15 ssh-keygen -B [-f input_keyfile]
16 ssh-keygen -D pkcs11
17 ssh-keygen -F hostname [-f known_hosts_file] [-l]
18 ssh-keygen -H [-f known_hosts_file]
19 ssh-keygen -R hostname [-f known_hosts_file]
20 ssh-keygen -r hostname [-f input_keyfile] [-g]
21 ssh-keygen -G output_file [-v] [-b bits] [-M memory] [-S start_point]
22 ssh-keygen -T output_file -f input_file [-v] [-a rounds] [-J num_lines]
23 [-j start_line] [-K checkpt] [-W generator]
24 ssh-keygen -s ca_key -I certificate_identity [-h] [-U]
25 [-D pkcs11_provider] [-n principals] [-O option]
26 [-V validity_interval] [-z serial_number] file ...
27 ssh-keygen -L [-f input_keyfile]
28 ssh-keygen -A [-f prefix_path]
29 ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number]
30 file ...
31 ssh-keygen -Q -f krl_file file ...
32
33DESCRIPTION
34 ssh-keygen generates, manages and converts authentication keys for
35 ssh(1). ssh-keygen can create keys for use by SSH protocol version 2.
36
37 The type of key to be generated is specified with the -t option. If
38 invoked without any arguments, ssh-keygen will generate an RSA key.
39
40 ssh-keygen is also used to generate groups for use in Diffie-Hellman
41 group exchange (DH-GEX). See the MODULI GENERATION section for details.
42
43 Finally, ssh-keygen can be used to generate and update Key Revocation
44 Lists, and to test whether given keys have been revoked by one. See the
45 KEY REVOCATION LISTS section for details.
46
47 Normally each user wishing to use SSH with public key authentication runs
48 this once to create the authentication key in ~/.ssh/id_dsa,
49 ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 or ~/.ssh/id_rsa. Additionally, the
50 system administrator may use this to generate host keys, as seen in
51 /etc/rc.
52
53 Normally this program generates the key and asks for a file in which to
54 store the private key. The public key is stored in a file with the same
55 name but M-bM-^@M-^\.pubM-bM-^@M-^] appended. The program also asks for a passphrase. The
56 passphrase may be empty to indicate no passphrase (host keys must have an
57 empty passphrase), or it may be a string of arbitrary length. A
58 passphrase is similar to a password, except it can be a phrase with a
59 series of words, punctuation, numbers, whitespace, or any string of
60 characters you want. Good passphrases are 10-30 characters long, are not
61 simple sentences or otherwise easily guessable (English prose has only
62 1-2 bits of entropy per character, and provides very bad passphrases),
63 and contain a mix of upper and lowercase letters, numbers, and non-
64 alphanumeric characters. The passphrase can be changed later by using
65 the -p option.
66
67 There is no way to recover a lost passphrase. If the passphrase is lost
68 or forgotten, a new key must be generated and the corresponding public
69 key copied to other machines.
70
71 For keys stored in the newer OpenSSH format, there is also a comment
72 field in the key file that is only for convenience to the user to help
73 identify the key. The comment can tell what the key is for, or whatever
74 is useful. The comment is initialized to M-bM-^@M-^\user@hostM-bM-^@M-^] when the key is
75 created, but can be changed using the -c option.
76
77 After a key is generated, instructions below detail where the keys should
78 be placed to be activated.
79
80 The options are as follows:
81
82 -A For each of the key types (rsa, dsa, ecdsa and ed25519) for which
83 host keys do not exist, generate the host keys with the default
84 key file path, an empty passphrase, default bits for the key
85 type, and default comment. If -f has also been specified, its
86 argument is used as a prefix to the default path for the
87 resulting host key files. This is used by /etc/rc to generate
88 new host keys.
89
90 -a rounds
91 When saving a new-format private key (i.e. an ed25519 key or when
92 the -o flag is set), this option specifies the number of KDF (key
93 derivation function) rounds used. Higher numbers result in
94 slower passphrase verification and increased resistance to brute-
95 force password cracking (should the keys be stolen).
96
97 When screening DH-GEX candidates (using the -T command). This
98 option specifies the number of primality tests to perform.
99
100 -B Show the bubblebabble digest of specified private or public key
101 file.
102
103 -b bits
104 Specifies the number of bits in the key to create. For RSA keys,
105 the minimum size is 1024 bits and the default is 2048 bits.
106 Generally, 2048 bits is considered sufficient. DSA keys must be
107 exactly 1024 bits as specified by FIPS 186-2. For ECDSA keys,
108 the -b flag determines the key length by selecting from one of
109 three elliptic curve sizes: 256, 384 or 521 bits. Attempting to
110 use bit lengths other than these three values for ECDSA keys will
111 fail. Ed25519 keys have a fixed length and the -b flag will be
112 ignored.
113
114 -C comment
115 Provides a new comment.
116
117 -c Requests changing the comment in the private and public key
118 files. This operation is only supported for keys stored in the
119 newer OpenSSH format. The program will prompt for the file
120 containing the private keys, for the passphrase if the key has
121 one, and for the new comment.
122
123 -D pkcs11
124 Download the RSA public keys provided by the PKCS#11 shared
125 library pkcs11. When used in combination with -s, this option
126 indicates that a CA key resides in a PKCS#11 token (see the
127 CERTIFICATES section for details).
128
129 -E fingerprint_hash
130 Specifies the hash algorithm used when displaying key
131 fingerprints. Valid options are: M-bM-^@M-^\md5M-bM-^@M-^] and M-bM-^@M-^\sha256M-bM-^@M-^]. The
132 default is M-bM-^@M-^\sha256M-bM-^@M-^].
133
134 -e This option will read a private or public OpenSSH key file and
135 print to stdout the key in one of the formats specified by the -m
136 option. The default export format is M-bM-^@M-^\RFC4716M-bM-^@M-^]. This option
137 allows exporting OpenSSH keys for use by other programs,
138 including several commercial SSH implementations.
139
140 -F hostname
141 Search for the specified hostname in a known_hosts file, listing
142 any occurrences found. This option is useful to find hashed host
143 names or addresses and may also be used in conjunction with the
144 -H option to print found keys in a hashed format.
145
146 -f filename
147 Specifies the filename of the key file.
148
149 -G output_file
150 Generate candidate primes for DH-GEX. These primes must be
151 screened for safety (using the -T option) before use.
152
153 -g Use generic DNS format when printing fingerprint resource records
154 using the -r command.
155
156 -H Hash a known_hosts file. This replaces all hostnames and
157 addresses with hashed representations within the specified file;
158 the original content is moved to a file with a .old suffix.
159 These hashes may be used normally by ssh and sshd, but they do
160 not reveal identifying information should the file's contents be
161 disclosed. This option will not modify existing hashed hostnames
162 and is therefore safe to use on files that mix hashed and non-
163 hashed names.
164
165 -h When signing a key, create a host certificate instead of a user
166 certificate. Please see the CERTIFICATES section for details.
167
168 -I certificate_identity
169 Specify the key identity when signing a public key. Please see
170 the CERTIFICATES section for details.
171
172 -i This option will read an unencrypted private (or public) key file
173 in the format specified by the -m option and print an OpenSSH
174 compatible private (or public) key to stdout. This option allows
175 importing keys from other software, including several commercial
176 SSH implementations. The default import format is M-bM-^@M-^\RFC4716M-bM-^@M-^].
177
178 -J num_lines
179 Exit after screening the specified number of lines while
180 performing DH candidate screening using the -T option.
181
182 -j start_line
183 Start screening at the specified line number while performing DH
184 candidate screening using the -T option.
185
186 -K checkpt
187 Write the last line processed to the file checkpt while
188 performing DH candidate screening using the -T option. This will
189 be used to skip lines in the input file that have already been
190 processed if the job is restarted.
191
192 -k Generate a KRL file. In this mode, ssh-keygen will generate a
193 KRL file at the location specified via the -f flag that revokes
194 every key or certificate presented on the command line.
195 Keys/certificates to be revoked may be specified by public key
196 file or using the format described in the KEY REVOCATION LISTS
197 section.
198
199 -L Prints the contents of one or more certificates.
200
201 -l Show fingerprint of specified public key file. For RSA and DSA
202 keys ssh-keygen tries to find the matching public key file and
203 prints its fingerprint. If combined with -v, a visual ASCII art
204 representation of the key is supplied with the fingerprint.
205
206 -M memory
207 Specify the amount of memory to use (in megabytes) when
208 generating candidate moduli for DH-GEX.
209
210 -m key_format
211 Specify a key format for the -i (import) or -e (export)
212 conversion options. The supported key formats are: M-bM-^@M-^\RFC4716M-bM-^@M-^]
213 (RFC 4716/SSH2 public or private key), M-bM-^@M-^\PKCS8M-bM-^@M-^] (PEM PKCS8 public
214 key) or M-bM-^@M-^\PEMM-bM-^@M-^] (PEM public key). The default conversion format is
215 M-bM-^@M-^\RFC4716M-bM-^@M-^].
216
217 -N new_passphrase
218 Provides the new passphrase.
219
220 -n principals
221 Specify one or more principals (user or host names) to be
222 included in a certificate when signing a key. Multiple
223 principals may be specified, separated by commas. Please see the
224 CERTIFICATES section for details.
225
226 -O option
227 Specify a certificate option when signing a key. This option may
228 be specified multiple times. See also the CERTIFICATES section
229 for further details. The options that are valid for user
230 certificates are:
231
232 clear Clear all enabled permissions. This is useful for
233 clearing the default set of permissions so permissions
234 may be added individually.
235
236 critical:name[=contents]
237 extension:name[=contents]
238 Includes an arbitrary certificate critical option or
239 extension. The specified name should include a domain
240 suffix, e.g. M-bM-^@M-^\name@example.comM-bM-^@M-^]. If contents is
241 specified then it is included as the contents of the
242 extension/option encoded as a string, otherwise the
243 extension/option is created with no contents (usually
244 indicating a flag). Extensions may be ignored by a
245 client or server that does not recognise them, whereas
246 unknown critical options will cause the certificate to be
247 refused.
248
249 At present, no standard options are valid for host keys.
250
251 force-command=command
252 Forces the execution of command instead of any shell or
253 command specified by the user when the certificate is
254 used for authentication.
255
256 no-agent-forwarding
257 Disable ssh-agent(1) forwarding (permitted by default).
258
259 no-port-forwarding
260 Disable port forwarding (permitted by default).
261
262 no-pty Disable PTY allocation (permitted by default).
263
264 no-user-rc
265 Disable execution of ~/.ssh/rc by sshd(8) (permitted by
266 default).
267
268 no-x11-forwarding
269 Disable X11 forwarding (permitted by default).
270
271 permit-agent-forwarding
272 Allows ssh-agent(1) forwarding.
273
274 permit-port-forwarding
275 Allows port forwarding.
276
277 permit-pty
278 Allows PTY allocation.
279
280 permit-user-rc
281 Allows execution of ~/.ssh/rc by sshd(8).
282
283 permit-x11-forwarding
284 Allows X11 forwarding.
285
286 source-address=address_list
287 Restrict the source addresses from which the certificate
288 is considered valid. The address_list is a comma-
289 separated list of one or more address/netmask pairs in
290 CIDR format.
291
292 -o Causes ssh-keygen to save private keys using the new OpenSSH
293 format rather than the more compatible PEM format. The new
294 format has increased resistance to brute-force password cracking
295 but is not supported by versions of OpenSSH prior to 6.5.
296 Ed25519 keys always use the new private key format.
297
298 -P passphrase
299 Provides the (old) passphrase.
300
301 -p Requests changing the passphrase of a private key file instead of
302 creating a new private key. The program will prompt for the file
303 containing the private key, for the old passphrase, and twice for
304 the new passphrase.
305
306 -Q Test whether keys have been revoked in a KRL.
307
308 -q Silence ssh-keygen.
309
310 -R hostname
311 Removes all keys belonging to hostname from a known_hosts file.
312 This option is useful to delete hashed hosts (see the -H option
313 above).
314
315 -r hostname
316 Print the SSHFP fingerprint resource record named hostname for
317 the specified public key file.
318
319 -S start
320 Specify start point (in hex) when generating candidate moduli for
321 DH-GEX.
322
323 -s ca_key
324 Certify (sign) a public key using the specified CA key. Please
325 see the CERTIFICATES section for details.
326
327 When generating a KRL, -s specifies a path to a CA public key
328 file used to revoke certificates directly by key ID or serial
329 number. See the KEY REVOCATION LISTS section for details.
330
331 -T output_file
332 Test DH group exchange candidate primes (generated using the -G
333 option) for safety.
334
335 -t dsa | ecdsa | ed25519 | rsa
336 Specifies the type of key to create. The possible values are
337 M-bM-^@M-^\dsaM-bM-^@M-^], M-bM-^@M-^\ecdsaM-bM-^@M-^], M-bM-^@M-^\ed25519M-bM-^@M-^], or M-bM-^@M-^\rsaM-bM-^@M-^].
338
339 -U When used in combination with -s, this option indicates that a CA
340 key resides in a ssh-agent(1). See the CERTIFICATES section for
341 more information.
342
343 -u Update a KRL. When specified with -k, keys listed via the
344 command line are added to the existing KRL rather than a new KRL
345 being created.
346
347 -V validity_interval
348 Specify a validity interval when signing a certificate. A
349 validity interval may consist of a single time, indicating that
350 the certificate is valid beginning now and expiring at that time,
351 or may consist of two times separated by a colon to indicate an
352 explicit time interval. The start time may be specified as a
353 date in YYYYMMDD format, a time in YYYYMMDDHHMMSS format or a
354 relative time (to the current time) consisting of a minus sign
355 followed by a relative time in the format described in the TIME
356 FORMATS section of sshd_config(5). The end time may be specified
357 as a YYYYMMDD date, a YYYYMMDDHHMMSS time or a relative time
358 starting with a plus character.
359
360 For example: M-bM-^@M-^\+52w1dM-bM-^@M-^] (valid from now to 52 weeks and one day
361 from now), M-bM-^@M-^\-4w:+4wM-bM-^@M-^] (valid from four weeks ago to four weeks
362 from now), M-bM-^@M-^\20100101123000:20110101123000M-bM-^@M-^] (valid from 12:30 PM,
363 January 1st, 2010 to 12:30 PM, January 1st, 2011), M-bM-^@M-^\-1d:20110101M-bM-^@M-^]
364 (valid from yesterday to midnight, January 1st, 2011).
365
366 -v Verbose mode. Causes ssh-keygen to print debugging messages
367 about its progress. This is helpful for debugging moduli
368 generation. Multiple -v options increase the verbosity. The
369 maximum is 3.
370
371 -W generator
372 Specify desired generator when testing candidate moduli for DH-
373 GEX.
374
375 -y This option will read a private OpenSSH format file and print an
376 OpenSSH public key to stdout.
377
378 -z serial_number
379 Specifies a serial number to be embedded in the certificate to
380 distinguish this certificate from others from the same CA. The
381 default serial number is zero.
382
383 When generating a KRL, the -z flag is used to specify a KRL
384 version number.
385
386MODULI GENERATION
387 ssh-keygen may be used to generate groups for the Diffie-Hellman Group
388 Exchange (DH-GEX) protocol. Generating these groups is a two-step
389 process: first, candidate primes are generated using a fast, but memory
390 intensive process. These candidate primes are then tested for
391 suitability (a CPU-intensive process).
392
393 Generation of primes is performed using the -G option. The desired
394 length of the primes may be specified by the -b option. For example:
395
396 # ssh-keygen -G moduli-2048.candidates -b 2048
397
398 By default, the search for primes begins at a random point in the desired
399 length range. This may be overridden using the -S option, which
400 specifies a different start point (in hex).
401
402 Once a set of candidates have been generated, they must be screened for
403 suitability. This may be performed using the -T option. In this mode
404 ssh-keygen will read candidates from standard input (or a file specified
405 using the -f option). For example:
406
407 # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
408
409 By default, each candidate will be subjected to 100 primality tests.
410 This may be overridden using the -a option. The DH generator value will
411 be chosen automatically for the prime under consideration. If a specific
412 generator is desired, it may be requested using the -W option. Valid
413 generator values are 2, 3, and 5.
414
415 Screened DH groups may be installed in /etc/moduli. It is important that
416 this file contains moduli of a range of bit lengths and that both ends of
417 a connection share common moduli.
418
419CERTIFICATES
420 ssh-keygen supports signing of keys to produce certificates that may be
421 used for user or host authentication. Certificates consist of a public
422 key, some identity information, zero or more principal (user or host)
423 names and a set of options that are signed by a Certification Authority
424 (CA) key. Clients or servers may then trust only the CA key and verify
425 its signature on a certificate rather than trusting many user/host keys.
426 Note that OpenSSH certificates are a different, and much simpler, format
427 to the X.509 certificates used in ssl(8).
428
429 ssh-keygen supports two types of certificates: user and host. User
430 certificates authenticate users to servers, whereas host certificates
431 authenticate server hosts to users. To generate a user certificate:
432
433 $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
434
435 The resultant certificate will be placed in /path/to/user_key-cert.pub.
436 A host certificate requires the -h option:
437
438 $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
439
440 The host certificate will be output to /path/to/host_key-cert.pub.
441
442 It is possible to sign using a CA key stored in a PKCS#11 token by
443 providing the token library using -D and identifying the CA key by
444 providing its public half as an argument to -s:
445
446 $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub
447
448 Similarly, it is possible for the CA key to be hosted in a ssh-agent(1).
449 This is indicated by the -U flag and, again, the CA key must be
450 identified by its public half.
451
452 $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub
453
454 In all cases, key_id is a "key identifier" that is logged by the server
455 when the certificate is used for authentication.
456
457 Certificates may be limited to be valid for a set of principal
458 (user/host) names. By default, generated certificates are valid for all
459 users or hosts. To generate a certificate for a specified set of
460 principals:
461
462 $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
463 $ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub
464
465 Additional limitations on the validity and use of user certificates may
466 be specified through certificate options. A certificate option may
467 disable features of the SSH session, may be valid only when presented
468 from particular source addresses or may force the use of a specific
469 command. For a list of valid certificate options, see the documentation
470 for the -O option above.
471
472 Finally, certificates may be defined with a validity lifetime. The -V
473 option allows specification of certificate start and end times. A
474 certificate that is presented at a time outside this range will not be
475 considered valid. By default, certificates are valid from UNIX Epoch to
476 the distant future.
477
478 For certificates to be used for user or host authentication, the CA
479 public key must be trusted by sshd(8) or ssh(1). Please refer to those
480 manual pages for details.
481
482KEY REVOCATION LISTS
483 ssh-keygen is able to manage OpenSSH format Key Revocation Lists (KRLs).
484 These binary files specify keys or certificates to be revoked using a
485 compact format, taking as little as one bit per certificate if they are
486 being revoked by serial number.
487
488 KRLs may be generated using the -k flag. This option reads one or more
489 files from the command line and generates a new KRL. The files may
490 either contain a KRL specification (see below) or public keys, listed one
491 per line. Plain public keys are revoked by listing their hash or
492 contents in the KRL and certificates revoked by serial number or key ID
493 (if the serial is zero or not available).
494
495 Revoking keys using a KRL specification offers explicit control over the
496 types of record used to revoke keys and may be used to directly revoke
497 certificates by serial number or key ID without having the complete
498 original certificate on hand. A KRL specification consists of lines
499 containing one of the following directives followed by a colon and some
500 directive-specific information.
501
502 serial: serial_number[-serial_number]
503 Revokes a certificate with the specified serial number. Serial
504 numbers are 64-bit values, not including zero and may be
505 expressed in decimal, hex or octal. If two serial numbers are
506 specified separated by a hyphen, then the range of serial numbers
507 including and between each is revoked. The CA key must have been
508 specified on the ssh-keygen command line using the -s option.
509
510 id: key_id
511 Revokes a certificate with the specified key ID string. The CA
512 key must have been specified on the ssh-keygen command line using
513 the -s option.
514
515 key: public_key
516 Revokes the specified key. If a certificate is listed, then it
517 is revoked as a plain public key.
518
519 sha1: public_key
520 Revokes the specified key by its SHA1 hash.
521
522 KRLs may be updated using the -u flag in addition to -k. When this
523 option is specified, keys listed via the command line are merged into the
524 KRL, adding to those already there.
525
526 It is also possible, given a KRL, to test whether it revokes a particular
527 key (or keys). The -Q flag will query an existing KRL, testing each key
528 specified on the command line. If any key listed on the command line has
529 been revoked (or an error encountered) then ssh-keygen will exit with a
530 non-zero exit status. A zero exit status will only be returned if no key
531 was revoked.
532
533FILES
534 ~/.ssh/id_dsa
535 ~/.ssh/id_ecdsa
536 ~/.ssh/id_ed25519
537 ~/.ssh/id_rsa
538 Contains the DSA, ECDSA, Ed25519 or RSA authentication identity
539 of the user. This file should not be readable by anyone but the
540 user. It is possible to specify a passphrase when generating the
541 key; that passphrase will be used to encrypt the private part of
542 this file using 128-bit AES. This file is not automatically
543 accessed by ssh-keygen but it is offered as the default file for
544 the private key. ssh(1) will read this file when a login attempt
545 is made.
546
547 ~/.ssh/id_dsa.pub
548 ~/.ssh/id_ecdsa.pub
549 ~/.ssh/id_ed25519.pub
550 ~/.ssh/id_rsa.pub
551 Contains the DSA, ECDSA, Ed25519 or RSA public key for
552 authentication. The contents of this file should be added to
553 ~/.ssh/authorized_keys on all machines where the user wishes to
554 log in using public key authentication. There is no need to keep
555 the contents of this file secret.
556
557 /etc/moduli
558 Contains Diffie-Hellman groups used for DH-GEX. The file format
559 is described in moduli(5).
560
561SEE ALSO
562 ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
563
564 The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006.
565
566AUTHORS
567 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
568 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
569 de Raadt and Dug Song removed many bugs, re-added newer features and
570 created OpenSSH. Markus Friedl contributed the support for SSH protocol
571 versions 1.5 and 2.0.
572
573OpenBSD 6.2 July 8, 2017 OpenBSD 6.2