1 .\" $OpenBSD: ssh-keygen.1,v 1.78 2008/06/12 19:10:09 jmc Exp $
5 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
6 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
7 .\" All rights reserved
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".
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.
20 .\" Redistribution and use in source and binary forms, with or without
21 .\" modification, are permitted provided that the following conditions
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.
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.
40 .Dd $Mdocdate: June 12 2008 $
45 .Nd authentication key generation, management and conversion
52 .Op Fl N Ar new_passphrase
54 .Op Fl f Ar output_keyfile
58 .Op Fl P Ar old_passphrase
59 .Op Fl N Ar new_passphrase
63 .Op Fl f Ar input_keyfile
66 .Op Fl f Ar input_keyfile
69 .Op Fl f Ar input_keyfile
72 .Op Fl P Ar passphrase
77 .Op Fl f Ar input_keyfile
80 .Op Fl f Ar input_keyfile
85 .Op Fl f Ar known_hosts_file
88 .Op Fl f Ar known_hosts_file
91 .Op Fl f Ar known_hosts_file
94 .Op Fl f Ar input_keyfile
97 .Op Fl f Ar input_keyfile
104 .Op Fl S Ar start_point
109 .Op Fl a Ar num_trials
110 .Op Fl W Ar generator
113 generates, manages and converts authentication keys for
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
121 If invoked without any arguments,
123 will generate an RSA key for use in SSH protocol 2 connections.
126 is also used to generate groups for use in Diffie-Hellman group
129 .Sx MODULI GENERATION
132 Normally each user wishing to use SSH
133 with RSA or DSA authentication runs this once to create the authentication
135 .Pa ~/.ssh/identity ,
139 Additionally, the system administrator may use this to generate host keys,
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
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
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
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
164 There is no way to recover a lost passphrase.
166 lost or forgotten, a new key must be generated and copied to the
167 corresponding public key to other machines.
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
175 when the key is created, but can be changed using the
179 After a key is generated, instructions below detail where the keys
180 should be placed to be activated.
182 The options are as follows:
185 Specifies the number of primality tests to perform when screening DH-GEX
190 Show the bubblebabble digest of specified private or public key file.
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.
197 Provides a new comment.
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.
204 Download the RSA public key stored in the smartcard in
207 This option will read a private or public OpenSSH key file and
209 RFC 4716 SSH Public Key File Format
211 This option allows exporting keys for use by several commercial
214 Search for the specified
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
222 option to print found keys in a hashed format.
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
232 Use generic DNS format when printing fingerprint resource records using the
239 This replaces all hostnames and addresses with hashed representations
240 within the specified file; the original content is moved to a file with
242 These hashes may be used normally by
246 but they do not reveal identifying information should the file's contents
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.
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.
256 RFC 4716 SSH Public Key File Format.
257 This option allows importing keys from several commercial
260 Show fingerprint of specified public key file.
261 Private RSA1 keys are also supported.
264 tries to find the matching public key file and prints its fingerprint.
267 an ASCII art representation of the key is supplied with the fingerprint.
269 Specify the amount of memory to use (in megabytes) when generating
270 candidate moduli for DH-GEX.
271 .It Fl N Ar new_passphrase
272 Provides the new passphrase.
273 .It Fl P Ar passphrase
274 Provides the (old) passphrase.
276 Requests changing the passphrase of a private key file instead of
277 creating a new private key.
278 The program will prompt for the file
279 containing the private key, for the old passphrase, and twice for the
286 when creating a new key.
288 Removes all keys belonging to
293 This option is useful to delete hashed hosts (see the
297 Print the SSHFP fingerprint resource record named
299 for the specified public key file.
301 Specify start point (in hex) when generating candidate moduli for DH-GEX.
302 .It Fl T Ar output_file
303 Test DH group exchange candidate primes (generated using the
307 Specifies the type of key to create.
308 The possible values are
310 for protocol version 1 and
314 for protocol version 2.
316 Upload an existing RSA private key into the smartcard in
322 to print debugging messages about its progress.
323 This is helpful for debugging moduli generation.
326 options increase the verbosity.
328 .It Fl W Ar generator
329 Specify desired generator when testing candidate moduli for DH-GEX.
331 This option will read a private
332 OpenSSH format file and print an OpenSSH public key to stdout.
334 .Sh MODULI GENERATION
336 may be used to generate groups for the Diffie-Hellman Group Exchange
338 Generating these groups is a two-step process: first, candidate
339 primes are generated using a fast, but memory intensive process.
340 These candidate primes are then tested for suitability (a CPU-intensive
343 Generation of primes is performed using the
346 The desired length of the primes may be specified by the
351 .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
353 By default, the search for primes begins at a random point in the
354 desired length range.
355 This may be overridden using the
357 option, which specifies a different start point (in hex).
359 Once a set of candidates have been generated, they must be tested for
361 This may be performed using the
366 will read candidates from standard input (or a file specified using the
371 .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
373 By default, each candidate will be subjected to 100 primality tests.
374 This may be overridden using the
377 The DH generator value will be chosen automatically for the
378 prime under consideration.
379 If a specific generator is desired, it may be requested using the
382 Valid generator values are 2, 3, and 5.
384 Screened DH groups may be installed in
386 It is important that this file contains moduli of a range of bit lengths and
387 that both ends of a connection share common moduli.
390 .It Pa ~/.ssh/identity
391 Contains the protocol version 1 RSA authentication identity of the user.
392 This file should not be readable by anyone but the user.
394 specify a passphrase when generating the key; that passphrase will be
395 used to encrypt the private part of this file using 3DES.
396 This file is not automatically accessed by
398 but it is offered as the default file for the private key.
400 will read this file when a login attempt is made.
401 .It Pa ~/.ssh/identity.pub
402 Contains the protocol version 1 RSA public key for authentication.
403 The contents of this file should be added to
404 .Pa ~/.ssh/authorized_keys
406 where the user wishes to log in using RSA authentication.
407 There is no need to keep the contents of this file secret.
409 Contains the protocol version 2 DSA authentication identity of the user.
410 This file should not be readable by anyone but the user.
412 specify a passphrase when generating the key; that passphrase will be
413 used to encrypt the private part of this file using 3DES.
414 This file is not automatically accessed by
416 but it is offered as the default file for the private key.
418 will read this file when a login attempt is made.
419 .It Pa ~/.ssh/id_dsa.pub
420 Contains the protocol version 2 DSA public key for authentication.
421 The contents of this file should be added to
422 .Pa ~/.ssh/authorized_keys
424 where the user wishes to log in using public key authentication.
425 There is no need to keep the contents of this file secret.
427 Contains the protocol version 2 RSA authentication identity of the user.
428 This file should not be readable by anyone but the user.
430 specify a passphrase when generating the key; that passphrase will be
431 used to encrypt the private part of this file using 3DES.
432 This file is not automatically accessed by
434 but it is offered as the default file for the private key.
436 will read this file when a login attempt is made.
437 .It Pa ~/.ssh/id_rsa.pub
438 Contains the protocol version 2 RSA public key for authentication.
439 The contents of this file should be added to
440 .Pa ~/.ssh/authorized_keys
442 where the user wishes to log in using public key authentication.
443 There is no need to keep the contents of this file secret.
445 Contains Diffie-Hellman groups used for DH-GEX.
446 The file format is described in
457 .%T "The Secure Shell (SSH) Public Key File Format"
461 OpenSSH is a derivative of the original and free
462 ssh 1.2.12 release by Tatu Ylonen.
463 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
464 Theo de Raadt and Dug Song
465 removed many bugs, re-added newer features and
467 Markus Friedl contributed the support for SSH
468 protocol versions 1.5 and 2.0.