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1 | .\" $OpenBSD: ssh-keygen.1,v 1.75 2007/05/31 19:20:16 jmc 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 | .Nm ssh-keygen | |
87 | .Fl H | |
88 | .Op Fl f Ar known_hosts_file | |
89 | .Nm ssh-keygen | |
90 | .Fl R Ar hostname | |
91 | .Op Fl f Ar known_hosts_file | |
92 | .Nm ssh-keygen | |
93 | .Fl U Ar reader | |
94 | .Op Fl f Ar input_keyfile | |
95 | .Nm ssh-keygen | |
96 | .Fl r Ar hostname | |
97 | .Op Fl f Ar input_keyfile | |
98 | .Op Fl g | |
99 | .Nm ssh-keygen | |
100 | .Fl G Ar output_file | |
101 | .Op Fl v | |
102 | .Op Fl b Ar bits | |
103 | .Op Fl M Ar memory | |
104 | .Op Fl S Ar start_point | |
105 | .Nm ssh-keygen | |
106 | .Fl T Ar output_file | |
107 | .Fl f Ar input_file | |
108 | .Op Fl v | |
109 | .Op Fl a Ar num_trials | |
110 | .Op Fl W Ar generator | |
111 | .Sh DESCRIPTION | |
112 | .Nm | |
113 | generates, manages and converts authentication keys for | |
114 | .Xr ssh 1 . | |
115 | .Nm | |
116 | can create RSA keys for use by SSH protocol version 1 and RSA or DSA | |
117 | keys for use by SSH protocol version 2. | |
118 | The type of key to be generated is specified with the | |
119 | .Fl t | |
120 | option. | |
121 | If invoked without any arguments, | |
122 | .Nm | |
123 | will generate an RSA key for use in SSH protocol 2 connections. | |
124 | .Pp | |
125 | .Nm | |
126 | is also used to generate groups for use in Diffie-Hellman group | |
127 | exchange (DH-GEX). | |
128 | See the | |
129 | .Sx MODULI GENERATION | |
130 | section for details. | |
131 | .Pp | |
132 | Normally each user wishing to use SSH | |
133 | with RSA or DSA authentication runs this once to create the authentication | |
134 | key in | |
135 | .Pa ~/.ssh/identity , | |
136 | .Pa ~/.ssh/id_dsa | |
137 | or | |
138 | .Pa ~/.ssh/id_rsa . | |
139 | Additionally, the system administrator may use this to generate host keys, | |
140 | as seen in | |
141 | .Pa /etc/rc . | |
142 | .Pp | |
143 | Normally this program generates the key and asks for a file in which | |
144 | to store the private key. | |
145 | The public key is stored in a file with the same name but | |
146 | .Dq .pub | |
147 | appended. | |
148 | The program also asks for a passphrase. | |
149 | The passphrase may be empty to indicate no passphrase | |
150 | (host keys must have an empty passphrase), or it may be a string of | |
151 | arbitrary length. | |
152 | A passphrase is similar to a password, except it can be a phrase with a | |
153 | series of words, punctuation, numbers, whitespace, or any string of | |
154 | characters you want. | |
155 | Good passphrases are 10-30 characters long, are | |
156 | not simple sentences or otherwise easily guessable (English | |
157 | prose has only 1-2 bits of entropy per character, and provides very bad | |
158 | passphrases), and contain a mix of upper and lowercase letters, | |
159 | numbers, and non-alphanumeric characters. | |
160 | The passphrase can be changed later by using the | |
161 | .Fl p | |
162 | option. | |
163 | .Pp | |
164 | There is no way to recover a lost passphrase. | |
165 | If the passphrase is | |
166 | lost or forgotten, a new key must be generated and copied to the | |
167 | corresponding public key to other machines. | |
168 | .Pp | |
169 | For RSA1 keys, | |
170 | there is also a comment field in the key file that is only for | |
171 | convenience to the user to help identify the key. | |
172 | The comment can tell what the key is for, or whatever is useful. | |
173 | The comment is initialized to | |
174 | .Dq user@host | |
175 | when the key is created, but can be changed using the | |
176 | .Fl c | |
177 | option. | |
178 | .Pp | |
179 | After a key is generated, instructions below detail where the keys | |
180 | should be placed to be activated. | |
181 | .Pp | |
182 | The options are as follows: | |
183 | .Bl -tag -width Ds | |
184 | .It Fl a Ar trials | |
185 | Specifies the number of primality tests to perform when screening DH-GEX | |
186 | candidates using the | |
187 | .Fl T | |
188 | command. | |
189 | .It Fl B | |
190 | Show the bubblebabble digest of specified private or public key file. | |
191 | .It Fl b Ar bits | |
192 | Specifies the number of bits in the key to create. | |
193 | For RSA keys, the minimum size is 768 bits and the default is 2048 bits. | |
194 | Generally, 2048 bits is considered sufficient. | |
195 | DSA keys must be exactly 1024 bits as specified by FIPS 186-2. | |
196 | .It Fl C Ar comment | |
197 | Provides a new comment. | |
198 | .It Fl c | |
199 | Requests changing the comment in the private and public key files. | |
200 | This operation is only supported for RSA1 keys. | |
201 | The program will prompt for the file containing the private keys, for | |
202 | the passphrase if the key has one, and for the new comment. | |
203 | .It Fl D Ar reader | |
204 | Download the RSA public key stored in the smartcard in | |
205 | .Ar reader . | |
206 | .It Fl e | |
207 | This option will read a private or public OpenSSH key file and | |
208 | print the key in | |
209 | RFC 4716 SSH Public Key File Format | |
210 | to stdout. | |
211 | This option allows exporting keys for use by several commercial | |
212 | SSH implementations. | |
213 | .It Fl F Ar hostname | |
214 | Search for the specified | |
215 | .Ar hostname | |
216 | in a | |
217 | .Pa known_hosts | |
218 | file, listing any occurrences found. | |
219 | This option is useful to find hashed host names or addresses and may also be | |
220 | used in conjunction with the | |
221 | .Fl H | |
222 | option to print found keys in a hashed format. | |
223 | .It Fl f Ar filename | |
224 | Specifies the filename of the key file. | |
225 | .It Fl G Ar output_file | |
226 | Generate candidate primes for DH-GEX. | |
227 | These primes must be screened for | |
228 | safety (using the | |
229 | .Fl T | |
230 | option) before use. | |
231 | .It Fl g | |
232 | Use generic DNS format when printing fingerprint resource records using the | |
233 | .Fl r | |
234 | command. | |
235 | .It Fl H | |
236 | Hash a | |
237 | .Pa known_hosts | |
238 | file. | |
239 | This replaces all hostnames and addresses with hashed representations | |
240 | within the specified file; the original content is moved to a file with | |
241 | a .old suffix. | |
242 | These hashes may be used normally by | |
243 | .Nm ssh | |
244 | and | |
245 | .Nm sshd , | |
246 | but they do not reveal identifying information should the file's contents | |
247 | be disclosed. | |
248 | This option will not modify existing hashed hostnames and is therefore safe | |
249 | to use on files that mix hashed and non-hashed names. | |
250 | .It Fl i | |
251 | This option will read an unencrypted private (or public) key file | |
252 | in SSH2-compatible format and print an OpenSSH compatible private | |
253 | (or public) key to stdout. | |
254 | .Nm | |
255 | also reads the | |
256 | RFC 4716 SSH Public Key File Format. | |
257 | This option allows importing keys from several commercial | |
258 | SSH implementations. | |
259 | .It Fl l | |
260 | Show fingerprint of specified public key file. | |
261 | Private RSA1 keys are also supported. | |
262 | For RSA and DSA keys | |
263 | .Nm | |
264 | tries to find the matching public key file and prints its fingerprint. | |
265 | .It Fl M Ar memory | |
266 | Specify the amount of memory to use (in megabytes) when generating | |
267 | candidate moduli for DH-GEX. | |
268 | .It Fl N Ar new_passphrase | |
269 | Provides the new passphrase. | |
270 | .It Fl P Ar passphrase | |
271 | Provides the (old) passphrase. | |
272 | .It Fl p | |
273 | Requests changing the passphrase of a private key file instead of | |
274 | creating a new private key. | |
275 | The program will prompt for the file | |
276 | containing the private key, for the old passphrase, and twice for the | |
277 | new passphrase. | |
278 | .It Fl q | |
279 | Silence | |
280 | .Nm ssh-keygen . | |
281 | Used by | |
282 | .Pa /etc/rc | |
283 | when creating a new key. | |
284 | .It Fl R Ar hostname | |
285 | Removes all keys belonging to | |
286 | .Ar hostname | |
287 | from a | |
288 | .Pa known_hosts | |
289 | file. | |
290 | This option is useful to delete hashed hosts (see the | |
291 | .Fl H | |
292 | option above). | |
293 | .It Fl r Ar hostname | |
294 | Print the SSHFP fingerprint resource record named | |
295 | .Ar hostname | |
296 | for the specified public key file. | |
297 | .It Fl S Ar start | |
298 | Specify start point (in hex) when generating candidate moduli for DH-GEX. | |
299 | .It Fl T Ar output_file | |
300 | Test DH group exchange candidate primes (generated using the | |
301 | .Fl G | |
302 | option) for safety. | |
303 | .It Fl t Ar type | |
304 | Specifies the type of key to create. | |
305 | The possible values are | |
306 | .Dq rsa1 | |
307 | for protocol version 1 and | |
308 | .Dq rsa | |
309 | or | |
310 | .Dq dsa | |
311 | for protocol version 2. | |
312 | .It Fl U Ar reader | |
313 | Upload an existing RSA private key into the smartcard in | |
314 | .Ar reader . | |
315 | .It Fl v | |
316 | Verbose mode. | |
317 | Causes | |
318 | .Nm | |
319 | to print debugging messages about its progress. | |
320 | This is helpful for debugging moduli generation. | |
321 | Multiple | |
322 | .Fl v | |
323 | options increase the verbosity. | |
324 | The maximum is 3. | |
325 | .It Fl W Ar generator | |
326 | Specify desired generator when testing candidate moduli for DH-GEX. | |
327 | .It Fl y | |
328 | This option will read a private | |
329 | OpenSSH format file and print an OpenSSH public key to stdout. | |
330 | .El | |
331 | .Sh MODULI GENERATION | |
332 | .Nm | |
333 | may be used to generate groups for the Diffie-Hellman Group Exchange | |
334 | (DH-GEX) protocol. | |
335 | Generating these groups is a two-step process: first, candidate | |
336 | primes are generated using a fast, but memory intensive process. | |
337 | These candidate primes are then tested for suitability (a CPU-intensive | |
338 | process). | |
339 | .Pp | |
340 | Generation of primes is performed using the | |
341 | .Fl G | |
342 | option. | |
343 | The desired length of the primes may be specified by the | |
344 | .Fl b | |
345 | option. | |
346 | For example: | |
347 | .Pp | |
348 | .Dl # ssh-keygen -G moduli-2048.candidates -b 2048 | |
349 | .Pp | |
350 | By default, the search for primes begins at a random point in the | |
351 | desired length range. | |
352 | This may be overridden using the | |
353 | .Fl S | |
354 | option, which specifies a different start point (in hex). | |
355 | .Pp | |
356 | Once a set of candidates have been generated, they must be tested for | |
357 | suitability. | |
358 | This may be performed using the | |
359 | .Fl T | |
360 | option. | |
361 | In this mode | |
362 | .Nm | |
363 | will read candidates from standard input (or a file specified using the | |
364 | .Fl f | |
365 | option). | |
366 | For example: | |
367 | .Pp | |
368 | .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates | |
369 | .Pp | |
370 | By default, each candidate will be subjected to 100 primality tests. | |
371 | This may be overridden using the | |
372 | .Fl a | |
373 | option. | |
374 | The DH generator value will be chosen automatically for the | |
375 | prime under consideration. | |
376 | If a specific generator is desired, it may be requested using the | |
377 | .Fl W | |
378 | option. | |
379 | Valid generator values are 2, 3, and 5. | |
380 | .Pp | |
381 | Screened DH groups may be installed in | |
382 | .Pa /etc/moduli . | |
383 | It is important that this file contains moduli of a range of bit lengths and | |
384 | that both ends of a connection share common moduli. | |
385 | .Sh FILES | |
386 | .Bl -tag -width Ds | |
387 | .It Pa ~/.ssh/identity | |
388 | Contains the protocol version 1 RSA authentication identity of the user. | |
389 | This file should not be readable by anyone but the user. | |
390 | It is possible to | |
391 | specify a passphrase when generating the key; that passphrase will be | |
392 | used to encrypt the private part of this file using 3DES. | |
393 | This file is not automatically accessed by | |
394 | .Nm | |
395 | but it is offered as the default file for the private key. | |
396 | .Xr ssh 1 | |
397 | will read this file when a login attempt is made. | |
398 | .It Pa ~/.ssh/identity.pub | |
399 | Contains the protocol version 1 RSA public key for authentication. | |
400 | The contents of this file should be added to | |
401 | .Pa ~/.ssh/authorized_keys | |
402 | on all machines | |
403 | where the user wishes to log in using RSA authentication. | |
404 | There is no need to keep the contents of this file secret. | |
405 | .It Pa ~/.ssh/id_dsa | |
406 | Contains the protocol version 2 DSA authentication identity of the user. | |
407 | This file should not be readable by anyone but the user. | |
408 | It is possible to | |
409 | specify a passphrase when generating the key; that passphrase will be | |
410 | used to encrypt the private part of this file using 3DES. | |
411 | This file is not automatically accessed by | |
412 | .Nm | |
413 | but it is offered as the default file for the private key. | |
414 | .Xr ssh 1 | |
415 | will read this file when a login attempt is made. | |
416 | .It Pa ~/.ssh/id_dsa.pub | |
417 | Contains the protocol version 2 DSA public key for authentication. | |
418 | The contents of this file should be added to | |
419 | .Pa ~/.ssh/authorized_keys | |
420 | on all machines | |
421 | where the user wishes to log in using public key authentication. | |
422 | There is no need to keep the contents of this file secret. | |
423 | .It Pa ~/.ssh/id_rsa | |
424 | Contains the protocol version 2 RSA authentication identity of the user. | |
425 | This file should not be readable by anyone but the user. | |
426 | It is possible to | |
427 | specify a passphrase when generating the key; that passphrase will be | |
428 | used to encrypt the private part of this file using 3DES. | |
429 | This file is not automatically accessed by | |
430 | .Nm | |
431 | but it is offered as the default file for the private key. | |
432 | .Xr ssh 1 | |
433 | will read this file when a login attempt is made. | |
434 | .It Pa ~/.ssh/id_rsa.pub | |
435 | Contains the protocol version 2 RSA public key for authentication. | |
436 | The contents of this file should be added to | |
437 | .Pa ~/.ssh/authorized_keys | |
438 | on all machines | |
439 | where the user wishes to log in using public key authentication. | |
440 | There is no need to keep the contents of this file secret. | |
441 | .It Pa /etc/moduli | |
442 | Contains Diffie-Hellman groups used for DH-GEX. | |
443 | The file format is described in | |
444 | .Xr moduli 5 . | |
445 | .El | |
446 | .Sh SEE ALSO | |
447 | .Xr ssh 1 , | |
448 | .Xr ssh-add 1 , | |
449 | .Xr ssh-agent 1 , | |
450 | .Xr moduli 5 , | |
451 | .Xr sshd 8 | |
452 | .Rs | |
453 | .%R RFC 4716 | |
454 | .%T "The Secure Shell (SSH) Public Key File Format" | |
455 | .%D 2006 | |
456 | .Re | |
457 | .Sh AUTHORS | |
458 | OpenSSH is a derivative of the original and free | |
459 | ssh 1.2.12 release by Tatu Ylonen. | |
460 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
461 | Theo de Raadt and Dug Song | |
462 | removed many bugs, re-added newer features and | |
463 | created OpenSSH. | |
464 | Markus Friedl contributed the support for SSH | |
465 | protocol versions 1.5 and 2.0. |