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authorColin Watson <cjwatson@debian.org>2011-09-06 09:26:44 +0100
committerColin Watson <cjwatson@debian.org>2011-09-06 09:26:44 +0100
commite90790abaf031e037f444a6658e136e48577ea49 (patch)
tree79b50c1b36fa2592f8bd1e524751601de908de8d /ssh-keygen.0
parente21c9c2094733fc4778688766cf8ea3c9b473aca (diff)
parentafde81fe5d3d6d3e9721ec56981e0214ea850bc6 (diff)
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1SSH-KEYGEN(1) OpenBSD Reference Manual SSH-KEYGEN(1)
2
3NAME
4 ssh-keygen - authentication key generation, management and conversion
5
6SYNOPSIS
7 ssh-keygen [-q] [-b bits] -t type [-N new_passphrase] [-C comment]
8 [-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 [-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 num_trials]
23 [-W generator]
24 ssh-keygen -s ca_key -I certificate_identity [-h] [-n principals]
25 [-O option] [-V validity_interval] [-z serial_number] file ...
26 ssh-keygen -L [-f input_keyfile]
27 ssh-keygen -A
28
29DESCRIPTION
30 ssh-keygen generates, manages and converts authentication keys for
31 ssh(1). ssh-keygen can create RSA keys for use by SSH protocol version 1
32 and DSA, ECDSA or RSA keys for use by SSH protocol version 2. The type
33 of key to be generated is specified with the -t option. If invoked
34 without any arguments, ssh-keygen will generate an RSA key for use in SSH
35 protocol 2 connections.
36
37 ssh-keygen is also used to generate groups for use in Diffie-Hellman
38 group exchange (DH-GEX). See the MODULI GENERATION section for details.
39
40 Normally each user wishing to use SSH with public key authentication runs
41 this once to create the authentication key in ~/.ssh/identity,
42 ~/.ssh/id_ecdsa, ~/.ssh/id_dsa or ~/.ssh/id_rsa. Additionally, the
43 system administrator may use this to generate host keys, as seen in
44 /etc/rc.
45
46 Normally this program generates the key and asks for a file in which to
47 store the private key. The public key is stored in a file with the same
48 name but ``.pub'' appended. The program also asks for a passphrase. The
49 passphrase may be empty to indicate no passphrase (host keys must have an
50 empty passphrase), or it may be a string of arbitrary length. A
51 passphrase is similar to a password, except it can be a phrase with a
52 series of words, punctuation, numbers, whitespace, or any string of
53 characters you want. Good passphrases are 10-30 characters long, are not
54 simple sentences or otherwise easily guessable (English prose has only 1-
55 2 bits of entropy per character, and provides very bad passphrases), and
56 contain a mix of upper and lowercase letters, numbers, and non-
57 alphanumeric characters. The passphrase can be changed later by using
58 the -p option.
59
60 There is no way to recover a lost passphrase. If the passphrase is lost
61 or forgotten, a new key must be generated and the corresponding public
62 key copied to other machines.
63
64 For RSA1 keys, there is also a comment field in the key file that is only
65 for convenience to the user to help identify the key. The comment can
66 tell what the key is for, or whatever is useful. The comment is
67 initialized to ``user@host'' when the key is created, but can be changed
68 using the -c option.
69
70 After a key is generated, instructions below detail where the keys should
71 be placed to be activated.
72
73 The options are as follows:
74
75 -A For each of the key types (rsa1, rsa, dsa and ecdsa) for which
76 host keys do not exist, generate the host keys with the default
77 key file path, an empty passphrase, default bits for the key
78 type, and default comment. This is used by /etc/rc to generate
79 new host keys.
80
81 -a trials
82 Specifies the number of primality tests to perform when screening
83 DH-GEX candidates using the -T command.
84
85 -B Show the bubblebabble digest of specified private or public key
86 file.
87
88 -b bits
89 Specifies the number of bits in the key to create. For RSA keys,
90 the minimum size is 768 bits and the default is 2048 bits.
91 Generally, 2048 bits is considered sufficient. DSA keys must be
92 exactly 1024 bits as specified by FIPS 186-2. For ECDSA keys,
93 the -b flag determines they key length by selecting from one of
94 three elliptic curve sizes: 256, 384 or 521 bits. Attempting to
95 use bit lengths other than these three values for ECDSA keys will
96 fail.
97
98 -C comment
99 Provides a new comment.
100
101 -c Requests changing the comment in the private and public key
102 files. This operation is only supported for RSA1 keys. The
103 program will prompt for the file containing the private keys, for
104 the passphrase if the key has one, and for the new comment.
105
106 -D pkcs11
107 Download the RSA public keys provided by the PKCS#11 shared
108 library pkcs11. When used in combination with -s, this option
109 indicates that a CA key resides in a PKCS#11 token (see the
110 CERTIFICATES section for details).
111
112 -e This option will read a private or public OpenSSH key file and
113 print to stdout the key in one of the formats specified by the -m
114 option. The default export format is ``RFC4716''. This option
115 allows exporting OpenSSH keys for use by other programs,
116 including several commercial SSH implementations.
117
118 -F hostname
119 Search for the specified hostname in a known_hosts file, listing
120 any occurrences found. This option is useful to find hashed host
121 names or addresses and may also be used in conjunction with the
122 -H option to print found keys in a hashed format.
123
124 -f filename
125 Specifies the filename of the key file.
126
127 -G output_file
128 Generate candidate primes for DH-GEX. These primes must be
129 screened for safety (using the -T option) before use.
130
131 -g Use generic DNS format when printing fingerprint resource records
132 using the -r command.
133
134 -H Hash a known_hosts file. This replaces all hostnames and
135 addresses with hashed representations within the specified file;
136 the original content is moved to a file with a .old suffix.
137 These hashes may be used normally by ssh and sshd, but they do
138 not reveal identifying information should the file's contents be
139 disclosed. This option will not modify existing hashed hostnames
140 and is therefore safe to use on files that mix hashed and non-
141 hashed names.
142
143 -h When signing a key, create a host certificate instead of a user
144 certificate. Please see the CERTIFICATES section for details.
145
146 -I certificate_identity
147 Specify the key identity when signing a public key. Please see
148 the CERTIFICATES section for details.
149
150 -i This option will read an unencrypted private (or public) key file
151 in the format specified by the -m option and print an OpenSSH
152 compatible private (or public) key to stdout. This option allows
153 importing keys from other software, including several commercial
154 SSH implementations. The default import format is ``RFC4716''.
155
156 -L Prints the contents of a certificate.
157
158 -l Show fingerprint of specified public key file. Private RSA1 keys
159 are also supported. For RSA and DSA keys ssh-keygen tries to
160 find the matching public key file and prints its fingerprint. If
161 combined with -v, an ASCII art representation of the key is
162 supplied with the fingerprint.
163
164 -M memory
165 Specify the amount of memory to use (in megabytes) when
166 generating candidate moduli for DH-GEX.
167
168 -m key_format
169 Specify a key format for the -i (import) or -e (export)
170 conversion options. The supported key formats are: ``RFC4716''
171 (RFC 4716/SSH2 public or private key), ``PKCS8'' (PEM PKCS8
172 public key) or ``PEM'' (PEM public key). The default conversion
173 format is ``RFC4716''.
174
175 -N new_passphrase
176 Provides the new passphrase.
177
178 -n principals
179 Specify one or more principals (user or host names) to be
180 included in a certificate when signing a key. Multiple
181 principals may be specified, separated by commas. Please see the
182 CERTIFICATES section for details.
183
184 -O option
185 Specify a certificate option when signing a key. This option may
186 be specified multiple times. Please see the CERTIFICATES section
187 for details. The options that are valid for user certificates
188 are:
189
190 clear Clear all enabled permissions. This is useful for
191 clearing the default set of permissions so permissions
192 may be added individually.
193
194 force-command=command
195 Forces the execution of command instead of any shell or
196 command specified by the user when the certificate is
197 used for authentication.
198
199 no-agent-forwarding
200 Disable ssh-agent(1) forwarding (permitted by default).
201
202 no-port-forwarding
203 Disable port forwarding (permitted by default).
204
205 no-pty Disable PTY allocation (permitted by default).
206
207 no-user-rc
208 Disable execution of ~/.ssh/rc by sshd(8) (permitted by
209 default).
210
211 no-x11-forwarding
212 Disable X11 forwarding (permitted by default).
213
214 permit-agent-forwarding
215 Allows ssh-agent(1) forwarding.
216
217 permit-port-forwarding
218 Allows port forwarding.
219
220 permit-pty
221 Allows PTY allocation.
222
223 permit-user-rc
224 Allows execution of ~/.ssh/rc by sshd(8).
225
226 permit-x11-forwarding
227 Allows X11 forwarding.
228
229 source-address=address_list
230 Restrict the source addresses from which the certificate
231 is considered valid. The address_list is a comma-
232 separated list of one or more address/netmask pairs in
233 CIDR format.
234
235 At present, no options are valid for host keys.
236
237 -P passphrase
238 Provides the (old) passphrase.
239
240 -p Requests changing the passphrase of a private key file instead of
241 creating a new private key. The program will prompt for the file
242 containing the private key, for the old passphrase, and twice for
243 the new passphrase.
244
245 -q Silence ssh-keygen.
246
247 -R hostname
248 Removes all keys belonging to hostname from a known_hosts file.
249 This option is useful to delete hashed hosts (see the -H option
250 above).
251
252 -r hostname
253 Print the SSHFP fingerprint resource record named hostname for
254 the specified public key file.
255
256 -S start
257 Specify start point (in hex) when generating candidate moduli for
258 DH-GEX.
259
260 -s ca_key
261 Certify (sign) a public key using the specified CA key. Please
262 see the CERTIFICATES section for details.
263
264 -T output_file
265 Test DH group exchange candidate primes (generated using the -G
266 option) for safety.
267
268 -t type
269 Specifies the type of key to create. The possible values are
270 ``rsa1'' for protocol version 1 and ``dsa'', ``ecdsa'' or ``rsa''
271 for protocol version 2.
272
273 -V validity_interval
274 Specify a validity interval when signing a certificate. A
275 validity interval may consist of a single time, indicating that
276 the certificate is valid beginning now and expiring at that time,
277 or may consist of two times separated by a colon to indicate an
278 explicit time interval. The start time may be specified as a
279 date in YYYYMMDD format, a time in YYYYMMDDHHMMSS format or a
280 relative time (to the current time) consisting of a minus sign
281 followed by a relative time in the format described in the TIME
282 FORMATS section of sshd_config(5). The end time may be specified
283 as a YYYYMMDD date, a YYYYMMDDHHMMSS time or a relative time
284 starting with a plus character.
285
286 For example: ``+52w1d'' (valid from now to 52 weeks and one day
287 from now), ``-4w:+4w'' (valid from four weeks ago to four weeks
288 from now), ``20100101123000:20110101123000'' (valid from 12:30
289 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
290 ``-1d:20110101'' (valid from yesterday to midnight, January 1st,
291 2011).
292
293 -v Verbose mode. Causes ssh-keygen to print debugging messages
294 about its progress. This is helpful for debugging moduli
295 generation. Multiple -v options increase the verbosity. The
296 maximum is 3.
297
298 -W generator
299 Specify desired generator when testing candidate moduli for DH-
300 GEX.
301
302 -y This option will read a private OpenSSH format file and print an
303 OpenSSH public key to stdout.
304
305 -z serial_number
306 Specifies a serial number to be embedded in the certificate to
307 distinguish this certificate from others from the same CA. The
308 default serial number is zero.
309
310MODULI GENERATION
311 ssh-keygen may be used to generate groups for the Diffie-Hellman Group
312 Exchange (DH-GEX) protocol. Generating these groups is a two-step
313 process: first, candidate primes are generated using a fast, but memory
314 intensive process. These candidate primes are then tested for
315 suitability (a CPU-intensive process).
316
317 Generation of primes is performed using the -G option. The desired
318 length of the primes may be specified by the -b option. For example:
319
320 # ssh-keygen -G moduli-2048.candidates -b 2048
321
322 By default, the search for primes begins at a random point in the desired
323 length range. This may be overridden using the -S option, which
324 specifies a different start point (in hex).
325
326 Once a set of candidates have been generated, they must be tested for
327 suitability. This may be performed using the -T option. In this mode
328 ssh-keygen will read candidates from standard input (or a file specified
329 using the -f option). For example:
330
331 # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
332
333 By default, each candidate will be subjected to 100 primality tests.
334 This may be overridden using the -a option. The DH generator value will
335 be chosen automatically for the prime under consideration. If a specific
336 generator is desired, it may be requested using the -W option. Valid
337 generator values are 2, 3, and 5.
338
339 Screened DH groups may be installed in /etc/moduli. It is important that
340 this file contains moduli of a range of bit lengths and that both ends of
341 a connection share common moduli.
342
343CERTIFICATES
344 ssh-keygen supports signing of keys to produce certificates that may be
345 used for user or host authentication. Certificates consist of a public
346 key, some identity information, zero or more principal (user or host)
347 names and a set of options that are signed by a Certification Authority
348 (CA) key. Clients or servers may then trust only the CA key and verify
349 its signature on a certificate rather than trusting many user/host keys.
350 Note that OpenSSH certificates are a different, and much simpler, format
351 to the X.509 certificates used in ssl(8).
352
353 ssh-keygen supports two types of certificates: user and host. User
354 certificates authenticate users to servers, whereas host certificates
355 authenticate server hosts to users. To generate a user certificate:
356
357 $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
358
359 The resultant certificate will be placed in /path/to/user_key-cert.pub.
360 A host certificate requires the -h option:
361
362 $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
363
364 The host certificate will be output to /path/to/host_key-cert.pub.
365
366 It is possible to sign using a CA key stored in a PKCS#11 token by
367 providing the token library using -D and identifying the CA key by
368 providing its public half as an argument to -s:
369
370 $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id host_key.pub
371
372 In all cases, key_id is a "key identifier" that is logged by the server
373 when the certificate is used for authentication.
374
375 Certificates may be limited to be valid for a set of principal
376 (user/host) names. By default, generated certificates are valid for all
377 users or hosts. To generate a certificate for a specified set of
378 principals:
379
380 $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
381 $ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub
382
383 Additional limitations on the validity and use of user certificates may
384 be specified through certificate options. A certificate option may
385 disable features of the SSH session, may be valid only when presented
386 from particular source addresses or may force the use of a specific
387 command. For a list of valid certificate options, see the documentation
388 for the -O option above.
389
390 Finally, certificates may be defined with a validity lifetime. The -V
391 option allows specification of certificate start and end times. A
392 certificate that is presented at a time outside this range will not be
393 considered valid. By default, certificates have a maximum validity
394 interval.
395
396 For certificates to be used for user or host authentication, the CA
397 public key must be trusted by sshd(8) or ssh(1). Please refer to those
398 manual pages for details.
399
400FILES
401 ~/.ssh/identity
402 Contains the protocol version 1 RSA authentication identity of
403 the user. This file should not be readable by anyone but the
404 user. It is possible to specify a passphrase when generating the
405 key; that passphrase will be used to encrypt the private part of
406 this file using 3DES. This file is not automatically accessed by
407 ssh-keygen but it is offered as the default file for the private
408 key. ssh(1) will read this file when a login attempt is made.
409
410 ~/.ssh/identity.pub
411 Contains the protocol version 1 RSA public key for
412 authentication. The contents of this file should be added to
413 ~/.ssh/authorized_keys on all machines where the user wishes to
414 log in using RSA authentication. There is no need to keep the
415 contents of this file secret.
416
417 ~/.ssh/id_dsa
418 ~/.ssh/id_ecdsa
419 ~/.ssh/id_rsa
420 Contains the protocol version 2 DSA, ECDSA or RSA authentication
421 identity of the user. This file should not be readable by anyone
422 but the user. It is possible to specify a passphrase when
423 generating the key; that passphrase will be used to encrypt the
424 private part of this file using 128-bit AES. This file is not
425 automatically accessed by ssh-keygen but it is offered as the
426 default file for the private key. ssh(1) will read this file
427 when a login attempt is made.
428
429 ~/.ssh/id_dsa.pub
430 ~/.ssh/id_ecdsa.pub
431 ~/.ssh/id_rsa.pub
432 Contains the protocol version 2 DSA, ECDSA or RSA public key for
433 authentication. The contents of this file should be added to
434 ~/.ssh/authorized_keys on all machines where the user wishes to
435 log in using public key authentication. There is no need to keep
436 the contents of this file secret.
437
438 /etc/moduli
439 Contains Diffie-Hellman groups used for DH-GEX. The file format
440 is described in moduli(5).
441
442SEE ALSO
443 ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
444
445 The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006.
446
447AUTHORS
448 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
449 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
450 de Raadt and Dug Song removed many bugs, re-added newer features and
451 created OpenSSH. Markus Friedl contributed the support for SSH protocol
452 versions 1.5 and 2.0.
453
454OpenBSD 5.0 April 13, 2011 OpenBSD 5.0