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1 .\" $NetBSD$
2 .\" $OpenBSD: ssh-keygen.1,v 1.79 2008/07/24 23:55:30 sthen Exp $
3 .\"
4 .\" -*- nroff -*-
5 .\"
6 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
7 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
8 .\" All rights reserved
9 .\"
10 .\" As far as I am concerned, the code I have written for this software
11 .\" can be used freely for any purpose. Any derived versions of this
12 .\" software must be clearly marked as such, and if the derived work is
13 .\" incompatible with the protocol description in the RFC file, it must be
14 .\" called by a name other than "ssh" or "Secure Shell".
15 .\"
16 .\"
17 .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
18 .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
19 .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
20 .\"
21 .\" Redistribution and use in source and binary forms, with or without
22 .\" modification, are permitted provided that the following conditions
23 .\" are met:
24 .\" 1. Redistributions of source code must retain the above copyright
25 .\" notice, this list of conditions and the following disclaimer.
26 .\" 2. Redistributions in binary form must reproduce the above copyright
27 .\" notice, this list of conditions and the following disclaimer in the
28 .\" documentation and/or other materials provided with the distribution.
29 .\"
30 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
31 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
32 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
33 .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
34 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
35 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
36 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
37 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
38 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
39 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
40 .\"
41 .Dd July 24 2008
42 .Dt SSH-KEYGEN 1
43 .Os
44 .Sh NAME
45 .Nm ssh-keygen
46 .Nd authentication key generation, management and conversion
47 .Sh SYNOPSIS
48 .Nm ssh-keygen
49 .Bk -words
50 .Op Fl q
51 .Op Fl b Ar bits
52 .Fl t Ar type
53 .Op Fl N Ar new_passphrase
54 .Op Fl C Ar comment
55 .Op Fl f Ar output_keyfile
56 .Ek
57 .Nm ssh-keygen
58 .Fl p
59 .Op Fl P Ar old_passphrase
60 .Op Fl N Ar new_passphrase
61 .Op Fl f Ar keyfile
62 .Nm ssh-keygen
63 .Fl i
64 .Op Fl f Ar input_keyfile
65 .Nm ssh-keygen
66 .Fl e
67 .Op Fl f Ar input_keyfile
68 .Nm ssh-keygen
69 .Fl y
70 .Op Fl f Ar input_keyfile
71 .Nm ssh-keygen
72 .Fl c
73 .Op Fl P Ar passphrase
74 .Op Fl C Ar comment
75 .Op Fl f Ar keyfile
76 .Nm ssh-keygen
77 .Fl l
78 .Op Fl f Ar input_keyfile
79 .Nm ssh-keygen
80 .Fl B
81 .Op Fl f Ar input_keyfile
82 .Nm ssh-keygen
83 .Fl D Ar reader
84 .Nm ssh-keygen
85 .Fl F Ar hostname
86 .Op Fl f Ar known_hosts_file
87 .Op Fl l
88 .Nm ssh-keygen
89 .Fl H
90 .Op Fl f Ar known_hosts_file
91 .Nm ssh-keygen
92 .Fl R Ar hostname
93 .Op Fl f Ar known_hosts_file
94 .Nm ssh-keygen
95 .Fl U Ar reader
96 .Op Fl f Ar input_keyfile
97 .Nm ssh-keygen
98 .Fl r Ar hostname
99 .Op Fl f Ar input_keyfile
100 .Op Fl g
101 .Nm ssh-keygen
102 .Fl G Ar output_file
103 .Op Fl v
104 .Op Fl b Ar bits
105 .Op Fl M Ar memory
106 .Op Fl S Ar start_point
107 .Nm ssh-keygen
108 .Fl T Ar output_file
109 .Fl f Ar input_file
110 .Op Fl v
111 .Op Fl a Ar num_trials
112 .Op Fl W Ar generator
113 .Sh DESCRIPTION
114 .Nm
115 generates, manages and converts authentication keys for
116 .Xr ssh 1 .
117 .Nm
118 can create RSA keys for use by SSH protocol version 1 and RSA or DSA
119 keys for use by SSH protocol version 2.
120 The type of key to be generated is specified with the
121 .Fl t
122 option.
123 If invoked without any arguments,
124 .Nm
125 will generate an RSA key for use in SSH protocol 2 connections.
126 .Pp
127 .Nm
128 is also used to generate groups for use in Diffie-Hellman group
129 exchange (DH-GEX).
130 See the
131 .Sx MODULI GENERATION
132 section for details.
133 .Pp
134 Normally each user wishing to use SSH
135 with RSA or DSA authentication runs this once to create the authentication
136 key in
137 .Pa ~/.ssh/identity ,
138 .Pa ~/.ssh/id_dsa
139 or
140 .Pa ~/.ssh/id_rsa .
141 Additionally, the system administrator may use this to generate host keys,
142 as seen in
143 .Pa /etc/rc.d/sshd .
144 .Pp
145 Normally this program generates the key and asks for a file in which
146 to store the private key.
147 The public key is stored in a file with the same name but
148 .Dq .pub
149 appended.
150 The program also asks for a passphrase.
151 The passphrase may be empty to indicate no passphrase
152 (host keys must have an empty passphrase), or it may be a string of
153 arbitrary length.
154 A passphrase is similar to a password, except it can be a phrase with a
155 series of words, punctuation, numbers, whitespace, or any string of
156 characters you want.
157 Good passphrases are 10-30 characters long, are
158 not simple sentences or otherwise easily guessable (English
159 prose has only 1-2 bits of entropy per character, and provides very bad
160 passphrases), and contain a mix of upper and lowercase letters,
161 numbers, and non-alphanumeric characters.
162 The passphrase can be changed later by using the
163 .Fl p
164 option.
165 .Pp
166 There is no way to recover a lost passphrase.
167 If the passphrase is
168 lost or forgotten, a new key must be generated and copied to the
169 corresponding public key to other machines.
170 .Pp
171 For RSA1 keys,
172 there is also a comment field in the key file that is only for
173 convenience to the user to help identify the key.
174 The comment can tell what the key is for, or whatever is useful.
175 The comment is initialized to
176 .Dq user@host
177 when the key is created, but can be changed using the
178 .Fl c
179 option.
180 .Pp
181 After a key is generated, instructions below detail where the keys
182 should be placed to be activated.
183 .Pp
184 The options are as follows:
185 .Bl -tag -width Ds
186 .It Fl a Ar trials
187 Specifies the number of primality tests to perform when screening DH-GEX
188 candidates using the
189 .Fl T
190 command.
191 .It Fl B
192 Show the bubblebabble digest of specified private or public key file.
193 .It Fl b Ar bits
194 Specifies the number of bits in the key to create.
195 For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
196 Generally, 2048 bits is considered sufficient.
197 DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
198 .It Fl C Ar comment
199 Provides a new comment.
200 .It Fl c
201 Requests changing the comment in the private and public key files.
202 This operation is only supported for RSA1 keys.
203 The program will prompt for the file containing the private keys, for
204 the passphrase if the key has one, and for the new comment.
205 .It Fl D Ar reader
206 Download the RSA public key stored in the smartcard in
207 .Ar reader .
208 .It Fl e
209 This option will read a private or public OpenSSH key file and
210 print the key in
211 RFC 4716 SSH Public Key File Format
212 to stdout.
213 This option allows exporting keys for use by several commercial
214 SSH implementations.
215 .It Fl F Ar hostname
216 Search for the specified
217 .Ar hostname
218 in a
219 .Pa known_hosts
220 file, listing any occurrences found.
221 This option is useful to find hashed host names or addresses and may also be
222 used in conjunction with the
223 .Fl H
224 option to print found keys in a hashed format.
225 .It Fl f Ar filename
226 Specifies the filename of the key file.
227 .It Fl G Ar output_file
228 Generate candidate primes for DH-GEX.
229 These primes must be screened for
230 safety (using the
231 .Fl T
232 option) before use.
233 .It Fl g
234 Use generic DNS format when printing fingerprint resource records using the
235 .Fl r
236 command.
237 .It Fl H
238 Hash a
239 .Pa known_hosts
240 file.
241 This replaces all hostnames and addresses with hashed representations
242 within the specified file; the original content is moved to a file with
243 a .old suffix.
244 These hashes may be used normally by
245 .Nm ssh
246 and
247 .Nm sshd ,
248 but they do not reveal identifying information should the file's contents
249 be disclosed.
250 This option will not modify existing hashed hostnames and is therefore safe
251 to use on files that mix hashed and non-hashed names.
252 .It Fl i
253 This option will read an unencrypted private (or public) key file
254 in SSH2-compatible format and print an OpenSSH compatible private
255 (or public) key to stdout.
256 .Nm
257 also reads the
258 RFC 4716 SSH Public Key File Format.
259 This option allows importing keys from several commercial
260 SSH implementations.
261 .It Fl l
262 Show fingerprint of specified public key file.
263 Private RSA1 keys are also supported.
264 For RSA and DSA keys
265 .Nm
266 tries to find the matching public key file and prints its fingerprint.
267 If combined with
268 .Fl v ,
269 an ASCII art representation of the key is supplied with the fingerprint.
270 .It Fl M Ar memory
271 Specify the amount of memory to use (in megabytes) when generating
272 candidate moduli for DH-GEX.
273 .It Fl N Ar new_passphrase
274 Provides the new passphrase.
275 .It Fl P Ar passphrase
276 Provides the (old) passphrase.
277 .It Fl p
278 Requests changing the passphrase of a private key file instead of
279 creating a new private key.
280 The program will prompt for the file
281 containing the private key, for the old passphrase, and twice for the
282 new passphrase.
283 .It Fl q
284 Silence
285 .Nm ssh-keygen .
286 Used by
287 .Pa /etc/rc.d/sshd
288 when creating a new key.
289 .It Fl R Ar hostname
290 Removes all keys belonging to
291 .Ar hostname
292 from a
293 .Pa known_hosts
294 file.
295 This option is useful to delete hashed hosts (see the
296 .Fl H
297 option above).
298 .It Fl r Ar hostname
299 Print the SSHFP fingerprint resource record named
300 .Ar hostname
301 for the specified public key file.
302 .It Fl S Ar start
303 Specify start point (in hex) when generating candidate moduli for DH-GEX.
304 .It Fl T Ar output_file
305 Test DH group exchange candidate primes (generated using the
306 .Fl G
307 option) for safety.
308 .It Fl t Ar type
309 Specifies the type of key to create.
310 The possible values are
311 .Dq rsa1
312 for protocol version 1 and
313 .Dq rsa
314 or
315 .Dq dsa
316 for protocol version 2.
317 .It Fl U Ar reader
318 Upload an existing RSA private key into the smartcard in
319 .Ar reader .
320 .It Fl v
321 Verbose mode.
322 Causes
323 .Nm
324 to print debugging messages about its progress.
325 This is helpful for debugging moduli generation.
326 Multiple
327 .Fl v
328 options increase the verbosity.
329 The maximum is 3.
330 .It Fl W Ar generator
331 Specify desired generator when testing candidate moduli for DH-GEX.
332 .It Fl y
333 This option will read a private
334 OpenSSH format file and print an OpenSSH public key to stdout.
335 .El
336 .Sh MODULI GENERATION
337 .Nm
338 may be used to generate groups for the Diffie-Hellman Group Exchange
339 (DH-GEX) protocol.
340 Generating these groups is a two-step process: first, candidate
341 primes are generated using a fast, but memory intensive process.
342 These candidate primes are then tested for suitability (a CPU-intensive
343 process).
344 .Pp
345 Generation of primes is performed using the
346 .Fl G
347 option.
348 The desired length of the primes may be specified by the
349 .Fl b
350 option.
351 For example:
352 .Pp
353 .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
354 .Pp
355 By default, the search for primes begins at a random point in the
356 desired length range.
357 This may be overridden using the
358 .Fl S
359 option, which specifies a different start point (in hex).
360 .Pp
361 Once a set of candidates have been generated, they must be tested for
362 suitability.
363 This may be performed using the
364 .Fl T
365 option.
366 In this mode
367 .Nm
368 will read candidates from standard input (or a file specified using the
369 .Fl f
370 option).
371 For example:
372 .Pp
373 .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
374 .Pp
375 By default, each candidate will be subjected to 100 primality tests.
376 This may be overridden using the
377 .Fl a
378 option.
379 The DH generator value will be chosen automatically for the
380 prime under consideration.
381 If a specific generator is desired, it may be requested using the
382 .Fl W
383 option.
384 Valid generator values are 2, 3, and 5.
385 .Pp
386 Screened DH groups may be installed in
387 .Pa /etc/moduli .
388 It is important that this file contains moduli of a range of bit lengths and
389 that both ends of a connection share common moduli.
390 .Sh FILES
391 .Bl -tag -width Ds
392 .It Pa ~/.ssh/identity
393 Contains the protocol version 1 RSA authentication identity of the user.
394 This file should not be readable by anyone but the user.
395 It is possible to
396 specify a passphrase when generating the key; that passphrase will be
397 used to encrypt the private part of this file using 3DES.
398 This file is not automatically accessed by
399 .Nm
400 but it is offered as the default file for the private key.
401 .Xr ssh 1
402 will read this file when a login attempt is made.
403 .It Pa ~/.ssh/identity.pub
404 Contains the protocol version 1 RSA public key for authentication.
405 The contents of this file should be added to
406 .Pa ~/.ssh/authorized_keys
407 on all machines
408 where the user wishes to log in using RSA authentication.
409 There is no need to keep the contents of this file secret.
410 .It Pa ~/.ssh/id_dsa
411 Contains the protocol version 2 DSA authentication identity of the user.
412 This file should not be readable by anyone but the user.
413 It is possible to
414 specify a passphrase when generating the key; that passphrase will be
415 used to encrypt the private part of this file using 3DES.
416 This file is not automatically accessed by
417 .Nm
418 but it is offered as the default file for the private key.
419 .Xr ssh 1
420 will read this file when a login attempt is made.
421 .It Pa ~/.ssh/id_dsa.pub
422 Contains the protocol version 2 DSA public key for authentication.
423 The contents of this file should be added to
424 .Pa ~/.ssh/authorized_keys
425 on all machines
426 where the user wishes to log in using public key authentication.
427 There is no need to keep the contents of this file secret.
428 .It Pa ~/.ssh/id_rsa
429 Contains the protocol version 2 RSA authentication identity of the user.
430 This file should not be readable by anyone but the user.
431 It is possible to
432 specify a passphrase when generating the key; that passphrase will be
433 used to encrypt the private part of this file using 3DES.
434 This file is not automatically accessed by
435 .Nm
436 but it is offered as the default file for the private key.
437 .Xr ssh 1
438 will read this file when a login attempt is made.
439 .It Pa ~/.ssh/id_rsa.pub
440 Contains the protocol version 2 RSA public key for authentication.
441 The contents of this file should be added to
442 .Pa ~/.ssh/authorized_keys
443 on all machines
444 where the user wishes to log in using public key authentication.
445 There is no need to keep the contents of this file secret.
446 .It Pa /etc/moduli
447 Contains Diffie-Hellman groups used for DH-GEX.
448 The file format is described in
449 .Xr moduli 5 .
450 .El
451 .Sh SEE ALSO
452 .Xr ssh 1 ,
453 .Xr ssh-add 1 ,
454 .Xr ssh-agent 1 ,
455 .Xr moduli 5 ,
456 .Xr sshd 8
457 .Rs
458 .%R RFC 4716
459 .%T "The Secure Shell (SSH) Public Key File Format"
460 .%D 2006
461 .Re
462 .Sh AUTHORS
463 OpenSSH is a derivative of the original and free
464 ssh 1.2.12 release by Tatu Ylonen.
465 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
466 Theo de Raadt and Dug Song
467 removed many bugs, re-added newer features and
468 created OpenSSH.
469 Markus Friedl contributed the support for SSH
470 protocol versions 1.5 and 2.0.