1 .\" $OpenBSD: ssh-keygen.1,v 1.101 2010/10/28 18:33:28 jmc Exp $
4 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
5 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
6 .\" All rights reserved
8 .\" As far as I am concerned, the code I have written for this software
9 .\" can be used freely for any purpose. Any derived versions of this
10 .\" software must be clearly marked as such, and if the derived work is
11 .\" incompatible with the protocol description in the RFC file, it must be
12 .\" called by a name other than "ssh" or "Secure Shell".
15 .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
16 .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
17 .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
19 .\" Redistribution and use in source and binary forms, with or without
20 .\" modification, are permitted provided that the following conditions
22 .\" 1. Redistributions of source code must retain the above copyright
23 .\" notice, this list of conditions and the following disclaimer.
24 .\" 2. Redistributions in binary form must reproduce the above copyright
25 .\" notice, this list of conditions and the following disclaimer in the
26 .\" documentation and/or other materials provided with the distribution.
28 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
29 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
30 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
31 .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
32 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
33 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
34 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
35 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
36 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
37 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
44 .Nd authentication key generation, management and conversion
51 .Op Fl N Ar new_passphrase
53 .Op Fl f Ar output_keyfile
56 .Op Fl P Ar old_passphrase
57 .Op Fl N Ar new_passphrase
61 .Op Fl m Ar key_format
62 .Op Fl f Ar input_keyfile
65 .Op Fl m Ar key_format
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
89 .Op Fl f Ar known_hosts_file
92 .Op Fl f Ar known_hosts_file
95 .Op Fl f Ar input_keyfile
102 .Op Fl S Ar start_point
107 .Op Fl a Ar num_trials
108 .Op Fl W Ar generator
111 .Fl I Ar certificate_identity
113 .Op Fl n Ar principals
115 .Op Fl V Ar validity_interval
116 .Op Fl z Ar serial_number
120 .Op Fl f Ar input_keyfile
124 generates, manages and converts authentication keys for
127 can create RSA keys for use by SSH protocol version 1 and DSA, ECDSA or RSA
128 keys for use by SSH protocol version 2.
129 The type of key to be generated is specified with the
132 If invoked without any arguments,
134 will generate an RSA key for use in SSH protocol 2 connections.
137 is also used to generate groups for use in Diffie-Hellman group
140 .Sx MODULI GENERATION
143 Normally each user wishing to use SSH
144 with public key authentication runs this once to create the authentication
146 .Pa ~/.ssh/identity ,
147 .Pa ~/.ssh/id_ecdsa ,
151 Additionally, the system administrator may use this to generate host keys,
155 Normally this program generates the key and asks for a file in which
156 to store the private key.
157 The public key is stored in a file with the same name but
160 The program also asks for a passphrase.
161 The passphrase may be empty to indicate no passphrase
162 (host keys must have an empty passphrase), or it may be a string of
164 A passphrase is similar to a password, except it can be a phrase with a
165 series of words, punctuation, numbers, whitespace, or any string of
167 Good passphrases are 10-30 characters long, are
168 not simple sentences or otherwise easily guessable (English
169 prose has only 1-2 bits of entropy per character, and provides very bad
170 passphrases), and contain a mix of upper and lowercase letters,
171 numbers, and non-alphanumeric characters.
172 The passphrase can be changed later by using the
176 There is no way to recover a lost passphrase.
178 lost or forgotten, a new key must be generated and copied to the
179 corresponding public key to other machines.
182 there is also a comment field in the key file that is only for
183 convenience to the user to help identify the key.
184 The comment can tell what the key is for, or whatever is useful.
185 The comment is initialized to
187 when the key is created, but can be changed using the
191 After a key is generated, instructions below detail where the keys
192 should be placed to be activated.
194 The options are as follows:
197 Specifies the number of primality tests to perform when screening DH-GEX
202 Show the bubblebabble digest of specified private or public key file.
204 Specifies the number of bits in the key to create.
205 For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
206 Generally, 2048 bits is considered sufficient.
207 DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
209 Provides a new comment.
211 Requests changing the comment in the private and public key files.
212 This operation is only supported for RSA1 keys.
213 The program will prompt for the file containing the private keys, for
214 the passphrase if the key has one, and for the new comment.
216 Download the RSA public keys provided by the PKCS#11 shared library
218 When used in combination with
220 this option indicates that a CA key resides in a PKCS#11 token (see the
222 section for details).
224 This option will read a private or public OpenSSH key file and
225 print to stdout the key in one of the formats specified by the
228 The default export format is
230 This option allows exporting OpenSSH keys for use by other programs, including
231 several commercial SSH implementations.
233 Search for the specified
237 file, listing any occurrences found.
238 This option is useful to find hashed host names or addresses and may also be
239 used in conjunction with the
241 option to print found keys in a hashed format.
243 Specifies the filename of the key file.
244 .It Fl G Ar output_file
245 Generate candidate primes for DH-GEX.
246 These primes must be screened for
251 Use generic DNS format when printing fingerprint resource records using the
258 This replaces all hostnames and addresses with hashed representations
259 within the specified file; the original content is moved to a file with
261 These hashes may be used normally by
265 but they do not reveal identifying information should the file's contents
267 This option will not modify existing hashed hostnames and is therefore safe
268 to use on files that mix hashed and non-hashed names.
270 When signing a key, create a host certificate instead of a user
275 .It Fl I Ar certificate_identity
276 Specify the key identity when signing a public key.
281 This option will read an unencrypted private (or public) key file
282 in the format specified by the
284 option and print an OpenSSH compatible private
285 (or public) key to stdout.
286 This option allows importing keys from other software, including several
287 commercial SSH implementations.
288 The default import format is
291 Prints the contents of a certificate.
293 Show fingerprint of specified public key file.
294 Private RSA1 keys are also supported.
297 tries to find the matching public key file and prints its fingerprint.
300 an ASCII art representation of the key is supplied with the fingerprint.
302 Specify the amount of memory to use (in megabytes) when generating
303 candidate moduli for DH-GEX.
304 .It Fl m Ar key_format
305 Specify a key format for the
309 (export) conversion options.
310 The supported key formats are:
312 (RFC 4716/SSH2 public or private key),
314 (PEM PKCS8 public key)
318 The default conversion format is
320 .It Fl N Ar new_passphrase
321 Provides the new passphrase.
322 .It Fl n Ar principals
323 Specify one or more principals (user or host names) to be included in
324 a certificate when signing a key.
325 Multiple principals may be specified, separated by commas.
330 Specify a certificate option when signing a key.
331 This option may be specified multiple times.
335 The options that are valid for user certificates are:
338 Clear all enabled permissions.
339 This is useful for clearing the default set of permissions so permissions may
340 be added individually.
341 .It Ic force-command Ns = Ns Ar command
342 Forces the execution of
344 instead of any shell or command specified by the user when
345 the certificate is used for authentication.
346 .It Ic no-agent-forwarding
349 forwarding (permitted by default).
350 .It Ic no-port-forwarding
351 Disable port forwarding (permitted by default).
353 Disable PTY allocation (permitted by default).
359 (permitted by default).
360 .It Ic no-x11-forwarding
361 Disable X11 forwarding (permitted by default).
362 .It Ic permit-agent-forwarding
366 .It Ic permit-port-forwarding
367 Allows port forwarding.
369 Allows PTY allocation.
370 .It Ic permit-user-rc
375 .It Ic permit-x11-forwarding
376 Allows X11 forwarding.
377 .It Ic source-address Ns = Ns Ar address_list
378 Restrict the source addresses from which the certificate is considered valid.
381 is a comma-separated list of one or more address/netmask pairs in CIDR
385 At present, no options are valid for host keys.
386 .It Fl P Ar passphrase
387 Provides the (old) passphrase.
389 Requests changing the passphrase of a private key file instead of
390 creating a new private key.
391 The program will prompt for the file
392 containing the private key, for the old passphrase, and twice for the
399 when creating a new key.
401 Removes all keys belonging to
406 This option is useful to delete hashed hosts (see the
410 Print the SSHFP fingerprint resource record named
412 for the specified public key file.
414 Specify start point (in hex) when generating candidate moduli for DH-GEX.
416 Certify (sign) a public key using the specified CA key.
420 .It Fl T Ar output_file
421 Test DH group exchange candidate primes (generated using the
425 Specifies the type of key to create.
426 The possible values are
428 for protocol version 1 and
433 for protocol version 2.
434 .It Fl V Ar validity_interval
435 Specify a validity interval when signing a certificate.
436 A validity interval may consist of a single time, indicating that the
437 certificate is valid beginning now and expiring at that time, or may consist
438 of two times separated by a colon to indicate an explicit time interval.
439 The start time may be specified as a date in YYYYMMDD format, a time
440 in YYYYMMDDHHMMSS format or a relative time (to the current time) consisting
441 of a minus sign followed by a relative time in the format described in the
445 The end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMMSS time or
446 a relative time starting with a plus character.
450 (valid from now to 52 weeks and one day from now),
452 (valid from four weeks ago to four weeks from now),
453 .Dq 20100101123000:20110101123000
454 (valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
456 (valid from yesterday to midnight, January 1st, 2011).
461 to print debugging messages about its progress.
462 This is helpful for debugging moduli generation.
465 options increase the verbosity.
467 .It Fl W Ar generator
468 Specify desired generator when testing candidate moduli for DH-GEX.
470 This option will read a private
471 OpenSSH format file and print an OpenSSH public key to stdout.
472 .It Fl z Ar serial_number
473 Specifies a serial number to be embedded in the certificate to distinguish
474 this certificate from others from the same CA.
475 The default serial number is zero.
477 .Sh MODULI GENERATION
479 may be used to generate groups for the Diffie-Hellman Group Exchange
481 Generating these groups is a two-step process: first, candidate
482 primes are generated using a fast, but memory intensive process.
483 These candidate primes are then tested for suitability (a CPU-intensive
486 Generation of primes is performed using the
489 The desired length of the primes may be specified by the
494 .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
496 By default, the search for primes begins at a random point in the
497 desired length range.
498 This may be overridden using the
500 option, which specifies a different start point (in hex).
502 Once a set of candidates have been generated, they must be tested for
504 This may be performed using the
509 will read candidates from standard input (or a file specified using the
514 .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
516 By default, each candidate will be subjected to 100 primality tests.
517 This may be overridden using the
520 The DH generator value will be chosen automatically for the
521 prime under consideration.
522 If a specific generator is desired, it may be requested using the
525 Valid generator values are 2, 3, and 5.
527 Screened DH groups may be installed in
529 It is important that this file contains moduli of a range of bit lengths and
530 that both ends of a connection share common moduli.
533 supports signing of keys to produce certificates that may be used for
534 user or host authentication.
535 Certificates consist of a public key, some identity information, zero or
536 more principal (user or host) names and a set of options that
537 are signed by a Certification Authority (CA) key.
538 Clients or servers may then trust only the CA key and verify its signature
539 on a certificate rather than trusting many user/host keys.
540 Note that OpenSSH certificates are a different, and much simpler, format to
541 the X.509 certificates used in
545 supports two types of certificates: user and host.
546 User certificates authenticate users to servers, whereas host certificates
547 authenticate server hosts to users.
548 To generate a user certificate:
550 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
552 The resultant certificate will be placed in
553 .Pa /path/to/user_key-cert.pub .
554 A host certificate requires the
558 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
560 The host certificate will be output to
561 .Pa /path/to/host_key-cert.pub .
563 It is possible to sign using a CA key stored in a PKCS#11 token by
564 providing the token library using
566 and identifying the CA key by providing its public half as an argument
570 .Dl $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id host_key.pub
574 is a "key identifier" that is logged by the server when the certificate
575 is used for authentication.
577 Certificates may be limited to be valid for a set of principal (user/host)
579 By default, generated certificates are valid for all users or hosts.
580 To generate a certificate for a specified set of principals:
582 .Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
583 .Dl "$ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub"
585 Additional limitations on the validity and use of user certificates may
586 be specified through certificate options.
587 A certificate option may disable features of the SSH session, may be
588 valid only when presented from particular source addresses or may
589 force the use of a specific command.
590 For a list of valid certificate options, see the documentation for the
594 Finally, certificates may be defined with a validity lifetime.
597 option allows specification of certificate start and end times.
598 A certificate that is presented at a time outside this range will not be
600 By default, certificates have a maximum validity interval.
602 For certificates to be used for user or host authentication, the CA
603 public key must be trusted by
607 Please refer to those manual pages for details.
609 .Bl -tag -width Ds -compact
610 .It Pa ~/.ssh/identity
611 Contains the protocol version 1 RSA authentication identity of the user.
612 This file should not be readable by anyone but the user.
614 specify a passphrase when generating the key; that passphrase will be
615 used to encrypt the private part of this file using 3DES.
616 This file is not automatically accessed by
618 but it is offered as the default file for the private key.
620 will read this file when a login attempt is made.
622 .It Pa ~/.ssh/identity.pub
623 Contains the protocol version 1 RSA public key for authentication.
624 The contents of this file should be added to
625 .Pa ~/.ssh/authorized_keys
627 where the user wishes to log in using RSA authentication.
628 There is no need to keep the contents of this file secret.
631 .It Pa ~/.ssh/id_ecdsa
633 Contains the protocol version 2 DSA, ECDSA or RSA authentication identity of the user.
634 This file should not be readable by anyone but the user.
636 specify a passphrase when generating the key; that passphrase will be
637 used to encrypt the private part of this file using 128-bit AES.
638 This file is not automatically accessed by
640 but it is offered as the default file for the private key.
642 will read this file when a login attempt is made.
644 .It Pa ~/.ssh/id_dsa.pub
645 .It Pa ~/.ssh/id_ecdsa.pub
646 .It Pa ~/.ssh/id_rsa.pub
647 Contains the protocol version 2 DSA, ECDSA or RSA public key for authentication.
648 The contents of this file should be added to
649 .Pa ~/.ssh/authorized_keys
651 where the user wishes to log in using public key authentication.
652 There is no need to keep the contents of this file secret.
655 Contains Diffie-Hellman groups used for DH-GEX.
656 The file format is described in
667 .%T "The Secure Shell (SSH) Public Key File Format"
671 OpenSSH is a derivative of the original and free
672 ssh 1.2.12 release by Tatu Ylonen.
673 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
674 Theo de Raadt and Dug Song
675 removed many bugs, re-added newer features and
677 Markus Friedl contributed the support for SSH
678 protocol versions 1.5 and 2.0.
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