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1 | .\" $OpenBSD: ssh-keygen.1,v 1.80 2009/10/24 00:48:34 dtucker Exp $ | |
2 | .\" | |
3 | .\" -*- nroff -*- | |
4 | .\" | |
5 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> | |
6 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland | |
7 | .\" All rights reserved | |
8 | .\" | |
9 | .\" As far as I am concerned, the code I have written for this software | |
10 | .\" can be used freely for any purpose. Any derived versions of this | |
11 | .\" software must be clearly marked as such, and if the derived work is | |
12 | .\" incompatible with the protocol description in the RFC file, it must be | |
13 | .\" called by a name other than "ssh" or "Secure Shell". | |
14 | .\" | |
15 | .\" | |
16 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. | |
17 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
18 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
19 | .\" | |
20 | .\" Redistribution and use in source and binary forms, with or without | |
21 | .\" modification, are permitted provided that the following conditions | |
22 | .\" are met: | |
23 | .\" 1. Redistributions of source code must retain the above copyright | |
24 | .\" notice, this list of conditions and the following disclaimer. | |
25 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
26 | .\" notice, this list of conditions and the following disclaimer in the | |
27 | .\" documentation and/or other materials provided with the distribution. | |
28 | .\" | |
29 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR | |
30 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
31 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
32 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
33 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
34 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
35 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
36 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
37 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
38 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
39 | .\" | |
40 | .Dd $Mdocdate$ | |
41 | .Dt SSH-KEYGEN 1 | |
42 | .Os | |
43 | .Sh NAME | |
44 | .Nm ssh-keygen | |
45 | .Nd authentication key generation, management and conversion | |
46 | .Sh SYNOPSIS | |
47 | .Nm ssh-keygen | |
48 | .Bk -words | |
49 | .Op Fl q | |
50 | .Op Fl b Ar bits | |
51 | .Fl t Ar type | |
52 | .Op Fl N Ar new_passphrase | |
53 | .Op Fl C Ar comment | |
54 | .Op Fl f Ar output_keyfile | |
55 | .Ek | |
56 | .Nm ssh-keygen | |
57 | .Fl p | |
58 | .Op Fl P Ar old_passphrase | |
59 | .Op Fl N Ar new_passphrase | |
60 | .Op Fl f Ar keyfile | |
61 | .Nm ssh-keygen | |
62 | .Fl i | |
63 | .Op Fl f Ar input_keyfile | |
64 | .Nm ssh-keygen | |
65 | .Fl e | |
66 | .Op Fl f Ar input_keyfile | |
67 | .Nm ssh-keygen | |
68 | .Fl y | |
69 | .Op Fl f Ar input_keyfile | |
70 | .Nm ssh-keygen | |
71 | .Fl c | |
72 | .Op Fl P Ar passphrase | |
73 | .Op Fl C Ar comment | |
74 | .Op Fl f Ar keyfile | |
75 | .Nm ssh-keygen | |
76 | .Fl l | |
77 | .Op Fl f Ar input_keyfile | |
78 | .Nm ssh-keygen | |
79 | .Fl B | |
80 | .Op Fl f Ar input_keyfile | |
81 | .Nm ssh-keygen | |
82 | .Fl D Ar reader | |
83 | .Nm ssh-keygen | |
84 | .Fl F Ar hostname | |
85 | .Op Fl f Ar known_hosts_file | |
86 | .Op Fl l | |
87 | .Nm ssh-keygen | |
88 | .Fl H | |
89 | .Op Fl f Ar known_hosts_file | |
90 | .Nm ssh-keygen | |
91 | .Fl R Ar hostname | |
92 | .Op Fl f Ar known_hosts_file | |
93 | .Nm ssh-keygen | |
94 | .Fl U Ar reader | |
95 | .Op Fl f Ar input_keyfile | |
96 | .Nm ssh-keygen | |
97 | .Fl r Ar hostname | |
98 | .Op Fl f Ar input_keyfile | |
99 | .Op Fl g | |
100 | .Nm ssh-keygen | |
101 | .Fl G Ar output_file | |
102 | .Op Fl v | |
103 | .Op Fl b Ar bits | |
104 | .Op Fl M Ar memory | |
105 | .Op Fl S Ar start_point | |
106 | .Nm ssh-keygen | |
107 | .Fl T Ar output_file | |
108 | .Fl f Ar input_file | |
109 | .Op Fl v | |
110 | .Op Fl a Ar num_trials | |
111 | .Op Fl W Ar generator | |
112 | .Sh DESCRIPTION | |
113 | .Nm | |
114 | generates, manages and converts authentication keys for | |
115 | .Xr ssh 1 . | |
116 | .Nm | |
117 | can create RSA keys for use by SSH protocol version 1 and RSA or DSA | |
118 | keys for use by SSH protocol version 2. | |
119 | The type of key to be generated is specified with the | |
120 | .Fl t | |
121 | option. | |
122 | If invoked without any arguments, | |
123 | .Nm | |
124 | will generate an RSA key for use in SSH protocol 2 connections. | |
125 | .Pp | |
126 | .Nm | |
127 | is also used to generate groups for use in Diffie-Hellman group | |
128 | exchange (DH-GEX). | |
129 | See the | |
130 | .Sx MODULI GENERATION | |
131 | section for details. | |
132 | .Pp | |
133 | Normally each user wishing to use SSH | |
134 | with RSA or DSA authentication runs this once to create the authentication | |
135 | key in | |
136 | .Pa ~/.ssh/identity , | |
137 | .Pa ~/.ssh/id_dsa | |
138 | or | |
139 | .Pa ~/.ssh/id_rsa . | |
140 | Additionally, the system administrator may use this to generate host keys, | |
141 | as seen in | |
142 | .Pa /etc/rc . | |
143 | .Pp | |
144 | Normally this program generates the key and asks for a file in which | |
145 | to store the private key. | |
146 | The public key is stored in a file with the same name but | |
147 | .Dq .pub | |
148 | appended. | |
149 | The program also asks for a passphrase. | |
150 | The passphrase may be empty to indicate no passphrase | |
151 | (host keys must have an empty passphrase), or it may be a string of | |
152 | arbitrary length. | |
153 | A passphrase is similar to a password, except it can be a phrase with a | |
154 | series of words, punctuation, numbers, whitespace, or any string of | |
155 | characters you want. | |
156 | Good passphrases are 10-30 characters long, are | |
157 | not simple sentences or otherwise easily guessable (English | |
158 | prose has only 1-2 bits of entropy per character, and provides very bad | |
159 | passphrases), and contain a mix of upper and lowercase letters, | |
160 | numbers, and non-alphanumeric characters. | |
161 | The passphrase can be changed later by using the | |
162 | .Fl p | |
163 | option. | |
164 | .Pp | |
165 | There is no way to recover a lost passphrase. | |
166 | If the passphrase is | |
167 | lost or forgotten, a new key must be generated and copied to the | |
168 | corresponding public key to other machines. | |
169 | .Pp | |
170 | For RSA1 keys, | |
171 | there is also a comment field in the key file that is only for | |
172 | convenience to the user to help identify the key. | |
173 | The comment can tell what the key is for, or whatever is useful. | |
174 | The comment is initialized to | |
175 | .Dq user@host | |
176 | when the key is created, but can be changed using the | |
177 | .Fl c | |
178 | option. | |
179 | .Pp | |
180 | After a key is generated, instructions below detail where the keys | |
181 | should be placed to be activated. | |
182 | .Pp | |
183 | The options are as follows: | |
184 | .Bl -tag -width Ds | |
185 | .It Fl a Ar trials | |
186 | Specifies the number of primality tests to perform when screening DH-GEX | |
187 | candidates using the | |
188 | .Fl T | |
189 | command. | |
190 | .It Fl B | |
191 | Show the bubblebabble digest of specified private or public key file. | |
192 | .It Fl b Ar bits | |
193 | Specifies the number of bits in the key to create. | |
194 | For RSA keys, the minimum size is 768 bits and the default is 2048 bits. | |
195 | Generally, 2048 bits is considered sufficient. | |
196 | DSA keys must be exactly 1024 bits as specified by FIPS 186-2. | |
197 | .It Fl C Ar comment | |
198 | Provides a new comment. | |
199 | .It Fl c | |
200 | Requests changing the comment in the private and public key files. | |
201 | This operation is only supported for RSA1 keys. | |
202 | The program will prompt for the file containing the private keys, for | |
203 | the passphrase if the key has one, and for the new comment. | |
204 | .It Fl D Ar reader | |
205 | Download the RSA public key stored in the smartcard in | |
206 | .Ar reader . | |
207 | .It Fl e | |
208 | This option will read a private or public OpenSSH key file and | |
209 | print the key in | |
210 | RFC 4716 SSH Public Key File Format | |
211 | to stdout. | |
212 | This option allows exporting keys for use by several commercial | |
213 | SSH implementations. | |
214 | .It Fl F Ar hostname | |
215 | Search for the specified | |
216 | .Ar hostname | |
217 | in a | |
218 | .Pa known_hosts | |
219 | file, listing any occurrences found. | |
220 | This option is useful to find hashed host names or addresses and may also be | |
221 | used in conjunction with the | |
222 | .Fl H | |
223 | option to print found keys in a hashed format. | |
224 | .It Fl f Ar filename | |
225 | Specifies the filename of the key file. | |
226 | .It Fl G Ar output_file | |
227 | Generate candidate primes for DH-GEX. | |
228 | These primes must be screened for | |
229 | safety (using the | |
230 | .Fl T | |
231 | option) before use. | |
232 | .It Fl g | |
233 | Use generic DNS format when printing fingerprint resource records using the | |
234 | .Fl r | |
235 | command. | |
236 | .It Fl H | |
237 | Hash a | |
238 | .Pa known_hosts | |
239 | file. | |
240 | This replaces all hostnames and addresses with hashed representations | |
241 | within the specified file; the original content is moved to a file with | |
242 | a .old suffix. | |
243 | These hashes may be used normally by | |
244 | .Nm ssh | |
245 | and | |
246 | .Nm sshd , | |
247 | but they do not reveal identifying information should the file's contents | |
248 | be disclosed. | |
249 | This option will not modify existing hashed hostnames and is therefore safe | |
250 | to use on files that mix hashed and non-hashed names. | |
251 | .It Fl i | |
252 | This option will read an unencrypted private (or public) key file | |
253 | in SSH2-compatible format and print an OpenSSH compatible private | |
254 | (or public) key to stdout. | |
255 | .Nm | |
256 | also reads the | |
257 | RFC 4716 SSH Public Key File Format. | |
258 | This option allows importing keys from several commercial | |
259 | SSH implementations. | |
260 | .It Fl l | |
261 | Show fingerprint of specified public key file. | |
262 | Private RSA1 keys are also supported. | |
263 | For RSA and DSA keys | |
264 | .Nm | |
265 | tries to find the matching public key file and prints its fingerprint. | |
266 | If combined with | |
267 | .Fl v , | |
268 | an ASCII art representation of the key is supplied with the fingerprint. | |
269 | .It Fl M Ar memory | |
270 | Specify the amount of memory to use (in megabytes) when generating | |
271 | candidate moduli for DH-GEX. | |
272 | .It Fl N Ar new_passphrase | |
273 | Provides the new passphrase. | |
274 | .It Fl P Ar passphrase | |
275 | Provides the (old) passphrase. | |
276 | .It Fl p | |
277 | Requests changing the passphrase of a private key file instead of | |
278 | creating a new private key. | |
279 | The program will prompt for the file | |
280 | containing the private key, for the old passphrase, and twice for the | |
281 | new passphrase. | |
282 | .It Fl q | |
283 | Silence | |
284 | .Nm ssh-keygen . | |
285 | Used by | |
286 | .Pa /etc/rc | |
287 | when creating a new key. | |
288 | .It Fl R Ar hostname | |
289 | Removes all keys belonging to | |
290 | .Ar hostname | |
291 | from a | |
292 | .Pa known_hosts | |
293 | file. | |
294 | This option is useful to delete hashed hosts (see the | |
295 | .Fl H | |
296 | option above). | |
297 | .It Fl r Ar hostname | |
298 | Print the SSHFP fingerprint resource record named | |
299 | .Ar hostname | |
300 | for the specified public key file. | |
301 | .It Fl S Ar start | |
302 | Specify start point (in hex) when generating candidate moduli for DH-GEX. | |
303 | .It Fl T Ar output_file | |
304 | Test DH group exchange candidate primes (generated using the | |
305 | .Fl G | |
306 | option) for safety. | |
307 | .It Fl t Ar type | |
308 | Specifies the type of key to create. | |
309 | The possible values are | |
310 | .Dq rsa1 | |
311 | for protocol version 1 and | |
312 | .Dq rsa | |
313 | or | |
314 | .Dq dsa | |
315 | for protocol version 2. | |
316 | .It Fl U Ar reader | |
317 | Upload an existing RSA private key into the smartcard in | |
318 | .Ar reader . | |
319 | .It Fl v | |
320 | Verbose mode. | |
321 | Causes | |
322 | .Nm | |
323 | to print debugging messages about its progress. | |
324 | This is helpful for debugging moduli generation. | |
325 | Multiple | |
326 | .Fl v | |
327 | options increase the verbosity. | |
328 | The maximum is 3. | |
329 | .It Fl W Ar generator | |
330 | Specify desired generator when testing candidate moduli for DH-GEX. | |
331 | .It Fl y | |
332 | This option will read a private | |
333 | OpenSSH format file and print an OpenSSH public key to stdout. | |
334 | .El | |
335 | .Sh MODULI GENERATION | |
336 | .Nm | |
337 | may be used to generate groups for the Diffie-Hellman Group Exchange | |
338 | (DH-GEX) protocol. | |
339 | Generating these groups is a two-step process: first, candidate | |
340 | primes are generated using a fast, but memory intensive process. | |
341 | These candidate primes are then tested for suitability (a CPU-intensive | |
342 | process). | |
343 | .Pp | |
344 | Generation of primes is performed using the | |
345 | .Fl G | |
346 | option. | |
347 | The desired length of the primes may be specified by the | |
348 | .Fl b | |
349 | option. | |
350 | For example: | |
351 | .Pp | |
352 | .Dl # ssh-keygen -G moduli-2048.candidates -b 2048 | |
353 | .Pp | |
354 | By default, the search for primes begins at a random point in the | |
355 | desired length range. | |
356 | This may be overridden using the | |
357 | .Fl S | |
358 | option, which specifies a different start point (in hex). | |
359 | .Pp | |
360 | Once a set of candidates have been generated, they must be tested for | |
361 | suitability. | |
362 | This may be performed using the | |
363 | .Fl T | |
364 | option. | |
365 | In this mode | |
366 | .Nm | |
367 | will read candidates from standard input (or a file specified using the | |
368 | .Fl f | |
369 | option). | |
370 | For example: | |
371 | .Pp | |
372 | .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates | |
373 | .Pp | |
374 | By default, each candidate will be subjected to 100 primality tests. | |
375 | This may be overridden using the | |
376 | .Fl a | |
377 | option. | |
378 | The DH generator value will be chosen automatically for the | |
379 | prime under consideration. | |
380 | If a specific generator is desired, it may be requested using the | |
381 | .Fl W | |
382 | option. | |
383 | Valid generator values are 2, 3, and 5. | |
384 | .Pp | |
385 | Screened DH groups may be installed in | |
386 | .Pa /etc/moduli . | |
387 | It is important that this file contains moduli of a range of bit lengths and | |
388 | that both ends of a connection share common moduli. | |
389 | .Sh FILES | |
390 | .Bl -tag -width Ds | |
391 | .It Pa ~/.ssh/identity | |
392 | Contains the protocol version 1 RSA authentication identity of the user. | |
393 | This file should not be readable by anyone but the user. | |
394 | It is possible to | |
395 | specify a passphrase when generating the key; that passphrase will be | |
396 | used to encrypt the private part of this file using 128-bit AES. | |
397 | This file is not automatically accessed by | |
398 | .Nm | |
399 | but it is offered as the default file for the private key. | |
400 | .Xr ssh 1 | |
401 | will read this file when a login attempt is made. | |
402 | .It Pa ~/.ssh/identity.pub | |
403 | Contains the protocol version 1 RSA public key for authentication. | |
404 | The contents of this file should be added to | |
405 | .Pa ~/.ssh/authorized_keys | |
406 | on all machines | |
407 | where the user wishes to log in using RSA authentication. | |
408 | There is no need to keep the contents of this file secret. | |
409 | .It Pa ~/.ssh/id_dsa | |
410 | Contains the protocol version 2 DSA authentication identity of the user. | |
411 | This file should not be readable by anyone but the user. | |
412 | It is possible to | |
413 | specify a passphrase when generating the key; that passphrase will be | |
414 | used to encrypt the private part of this file using 128-bit AES. | |
415 | This file is not automatically accessed by | |
416 | .Nm | |
417 | but it is offered as the default file for the private key. | |
418 | .Xr ssh 1 | |
419 | will read this file when a login attempt is made. | |
420 | .It Pa ~/.ssh/id_dsa.pub | |
421 | Contains the protocol version 2 DSA public key for authentication. | |
422 | The contents of this file should be added to | |
423 | .Pa ~/.ssh/authorized_keys | |
424 | on all machines | |
425 | where the user wishes to log in using public key authentication. | |
426 | There is no need to keep the contents of this file secret. | |
427 | .It Pa ~/.ssh/id_rsa | |
428 | Contains the protocol version 2 RSA authentication identity of the user. | |
429 | This file should not be readable by anyone but the user. | |
430 | It is possible to | |
431 | specify a passphrase when generating the key; that passphrase will be | |
432 | used to encrypt the private part of this file using 128-bit AES. | |
433 | This file is not automatically accessed by | |
434 | .Nm | |
435 | but it is offered as the default file for the private key. | |
436 | .Xr ssh 1 | |
437 | will read this file when a login attempt is made. | |
438 | .It Pa ~/.ssh/id_rsa.pub | |
439 | Contains the protocol version 2 RSA public key for authentication. | |
440 | The contents of this file should be added to | |
441 | .Pa ~/.ssh/authorized_keys | |
442 | on all machines | |
443 | where the user wishes to log in using public key authentication. | |
444 | There is no need to keep the contents of this file secret. | |
445 | .It Pa /etc/moduli | |
446 | Contains Diffie-Hellman groups used for DH-GEX. | |
447 | The file format is described in | |
448 | .Xr moduli 5 . | |
449 | .El | |
450 | .Sh SEE ALSO | |
451 | .Xr ssh 1 , | |
452 | .Xr ssh-add 1 , | |
453 | .Xr ssh-agent 1 , | |
454 | .Xr moduli 5 , | |
455 | .Xr sshd 8 | |
456 | .Rs | |
457 | .%R RFC 4716 | |
458 | .%T "The Secure Shell (SSH) Public Key File Format" | |
459 | .%D 2006 | |
460 | .Re | |
461 | .Sh AUTHORS | |
462 | OpenSSH is a derivative of the original and free | |
463 | ssh 1.2.12 release by Tatu Ylonen. | |
464 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
465 | Theo de Raadt and Dug Song | |
466 | removed many bugs, re-added newer features and | |
467 | created OpenSSH. | |
468 | Markus Friedl contributed the support for SSH | |
469 | protocol versions 1.5 and 2.0. |