1 .\" $OpenBSD: ssh-keygen.1,v 1.106 2011/04/13 04:09:37 djm 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
126 generates, manages and converts authentication keys for
129 can create RSA keys for use by SSH protocol version 1 and DSA, ECDSA or RSA
130 keys for use by SSH protocol version 2.
131 The type of key to be generated is specified with the
134 If invoked without any arguments,
136 will generate an RSA key for use in SSH protocol 2 connections.
139 is also used to generate groups for use in Diffie-Hellman group
142 .Sx MODULI GENERATION
145 Normally each user wishing to use SSH
146 with public key authentication runs this once to create the authentication
148 .Pa ~/.ssh/identity ,
149 .Pa ~/.ssh/id_ecdsa ,
153 Additionally, the system administrator may use this to generate host keys,
157 Normally this program generates the key and asks for a file in which
158 to store the private key.
159 The public key is stored in a file with the same name but
162 The program also asks for a passphrase.
163 The passphrase may be empty to indicate no passphrase
164 (host keys must have an empty passphrase), or it may be a string of
166 A passphrase is similar to a password, except it can be a phrase with a
167 series of words, punctuation, numbers, whitespace, or any string of
169 Good passphrases are 10-30 characters long, are
170 not simple sentences or otherwise easily guessable (English
171 prose has only 1-2 bits of entropy per character, and provides very bad
172 passphrases), and contain a mix of upper and lowercase letters,
173 numbers, and non-alphanumeric characters.
174 The passphrase can be changed later by using the
178 There is no way to recover a lost passphrase.
179 If the passphrase is lost or forgotten, a new key must be generated
180 and the corresponding public key copied to other machines.
183 there is also a comment field in the key file that is only for
184 convenience to the user to help identify the key.
185 The comment can tell what the key is for, or whatever is useful.
186 The comment is initialized to
188 when the key is created, but can be changed using the
192 After a key is generated, instructions below detail where the keys
193 should be placed to be activated.
195 The options are as follows:
198 For each of the key types (rsa1, rsa, dsa and ecdsa) for which host keys
199 do not exist, generate the host keys with the default key file path,
200 an empty passphrase, default bits for the key type, and default comment.
203 to generate new host keys.
205 Specifies the number of primality tests to perform when screening DH-GEX
210 Show the bubblebabble digest of specified private or public key file.
212 Specifies the number of bits in the key to create.
213 For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
214 Generally, 2048 bits is considered sufficient.
215 DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
218 flag determines they key length by selecting from one of three elliptic
219 curve sizes: 256, 384 or 521 bits.
220 Attempting to use bit lengths other than these three values for ECDSA keys
223 Provides a new comment.
225 Requests changing the comment in the private and public key files.
226 This operation is only supported for RSA1 keys.
227 The program will prompt for the file containing the private keys, for
228 the passphrase if the key has one, and for the new comment.
230 Download the RSA public keys provided by the PKCS#11 shared library
232 When used in combination with
234 this option indicates that a CA key resides in a PKCS#11 token (see the
236 section for details).
238 This option will read a private or public OpenSSH key file and
239 print to stdout the key in one of the formats specified by the
242 The default export format is
244 This option allows exporting OpenSSH keys for use by other programs, including
245 several commercial SSH implementations.
247 Search for the specified
251 file, listing any occurrences found.
252 This option is useful to find hashed host names or addresses and may also be
253 used in conjunction with the
255 option to print found keys in a hashed format.
257 Specifies the filename of the key file.
258 .It Fl G Ar output_file
259 Generate candidate primes for DH-GEX.
260 These primes must be screened for
265 Use generic DNS format when printing fingerprint resource records using the
272 This replaces all hostnames and addresses with hashed representations
273 within the specified file; the original content is moved to a file with
275 These hashes may be used normally by
279 but they do not reveal identifying information should the file's contents
281 This option will not modify existing hashed hostnames and is therefore safe
282 to use on files that mix hashed and non-hashed names.
284 When signing a key, create a host certificate instead of a user
289 .It Fl I Ar certificate_identity
290 Specify the key identity when signing a public key.
295 This option will read an unencrypted private (or public) key file
296 in the format specified by the
298 option and print an OpenSSH compatible private
299 (or public) key to stdout.
300 This option allows importing keys from other software, including several
301 commercial SSH implementations.
302 The default import format is
305 Prints the contents of a certificate.
307 Show fingerprint of specified public key file.
308 Private RSA1 keys are also supported.
311 tries to find the matching public key file and prints its fingerprint.
314 an ASCII art representation of the key is supplied with the fingerprint.
316 Specify the amount of memory to use (in megabytes) when generating
317 candidate moduli for DH-GEX.
318 .It Fl m Ar key_format
319 Specify a key format for the
323 (export) conversion options.
324 The supported key formats are:
326 (RFC 4716/SSH2 public or private key),
328 (PEM PKCS8 public key)
332 The default conversion format is
334 .It Fl N Ar new_passphrase
335 Provides the new passphrase.
336 .It Fl n Ar principals
337 Specify one or more principals (user or host names) to be included in
338 a certificate when signing a key.
339 Multiple principals may be specified, separated by commas.
344 Specify a certificate option when signing a key.
345 This option may be specified multiple times.
349 The options that are valid for user certificates are:
352 Clear all enabled permissions.
353 This is useful for clearing the default set of permissions so permissions may
354 be added individually.
355 .It Ic force-command Ns = Ns Ar command
356 Forces the execution of
358 instead of any shell or command specified by the user when
359 the certificate is used for authentication.
360 .It Ic no-agent-forwarding
363 forwarding (permitted by default).
364 .It Ic no-port-forwarding
365 Disable port forwarding (permitted by default).
367 Disable PTY allocation (permitted by default).
373 (permitted by default).
374 .It Ic no-x11-forwarding
375 Disable X11 forwarding (permitted by default).
376 .It Ic permit-agent-forwarding
380 .It Ic permit-port-forwarding
381 Allows port forwarding.
383 Allows PTY allocation.
384 .It Ic permit-user-rc
389 .It Ic permit-x11-forwarding
390 Allows X11 forwarding.
391 .It Ic source-address Ns = Ns Ar address_list
392 Restrict the source addresses from which the certificate is considered valid.
395 is a comma-separated list of one or more address/netmask pairs in CIDR
399 At present, no options are valid for host keys.
400 .It Fl P Ar passphrase
401 Provides the (old) passphrase.
403 Requests changing the passphrase of a private key file instead of
404 creating a new private key.
405 The program will prompt for the file
406 containing the private key, for the old passphrase, and twice for the
412 Removes all keys belonging to
417 This option is useful to delete hashed hosts (see the
421 Print the SSHFP fingerprint resource record named
423 for the specified public key file.
425 Specify start point (in hex) when generating candidate moduli for DH-GEX.
427 Certify (sign) a public key using the specified CA key.
431 .It Fl T Ar output_file
432 Test DH group exchange candidate primes (generated using the
436 Specifies the type of key to create.
437 The possible values are
439 for protocol version 1 and
444 for protocol version 2.
445 .It Fl V Ar validity_interval
446 Specify a validity interval when signing a certificate.
447 A validity interval may consist of a single time, indicating that the
448 certificate is valid beginning now and expiring at that time, or may consist
449 of two times separated by a colon to indicate an explicit time interval.
450 The start time may be specified as a date in YYYYMMDD format, a time
451 in YYYYMMDDHHMMSS format or a relative time (to the current time) consisting
452 of a minus sign followed by a relative time in the format described in the
456 The end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMMSS time or
457 a relative time starting with a plus character.
461 (valid from now to 52 weeks and one day from now),
463 (valid from four weeks ago to four weeks from now),
464 .Dq 20100101123000:20110101123000
465 (valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
467 (valid from yesterday to midnight, January 1st, 2011).
472 to print debugging messages about its progress.
473 This is helpful for debugging moduli generation.
476 options increase the verbosity.
478 .It Fl W Ar generator
479 Specify desired generator when testing candidate moduli for DH-GEX.
481 This option will read a private
482 OpenSSH format file and print an OpenSSH public key to stdout.
483 .It Fl z Ar serial_number
484 Specifies a serial number to be embedded in the certificate to distinguish
485 this certificate from others from the same CA.
486 The default serial number is zero.
488 .Sh MODULI GENERATION
490 may be used to generate groups for the Diffie-Hellman Group Exchange
492 Generating these groups is a two-step process: first, candidate
493 primes are generated using a fast, but memory intensive process.
494 These candidate primes are then tested for suitability (a CPU-intensive
497 Generation of primes is performed using the
500 The desired length of the primes may be specified by the
505 .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
507 By default, the search for primes begins at a random point in the
508 desired length range.
509 This may be overridden using the
511 option, which specifies a different start point (in hex).
513 Once a set of candidates have been generated, they must be tested for
515 This may be performed using the
520 will read candidates from standard input (or a file specified using the
525 .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
527 By default, each candidate will be subjected to 100 primality tests.
528 This may be overridden using the
531 The DH generator value will be chosen automatically for the
532 prime under consideration.
533 If a specific generator is desired, it may be requested using the
536 Valid generator values are 2, 3, and 5.
538 Screened DH groups may be installed in
540 It is important that this file contains moduli of a range of bit lengths and
541 that both ends of a connection share common moduli.
544 supports signing of keys to produce certificates that may be used for
545 user or host authentication.
546 Certificates consist of a public key, some identity information, zero or
547 more principal (user or host) names and a set of options that
548 are signed by a Certification Authority (CA) key.
549 Clients or servers may then trust only the CA key and verify its signature
550 on a certificate rather than trusting many user/host keys.
551 Note that OpenSSH certificates are a different, and much simpler, format to
552 the X.509 certificates used in
556 supports two types of certificates: user and host.
557 User certificates authenticate users to servers, whereas host certificates
558 authenticate server hosts to users.
559 To generate a user certificate:
561 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
563 The resultant certificate will be placed in
564 .Pa /path/to/user_key-cert.pub .
565 A host certificate requires the
569 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
571 The host certificate will be output to
572 .Pa /path/to/host_key-cert.pub .
574 It is possible to sign using a CA key stored in a PKCS#11 token by
575 providing the token library using
577 and identifying the CA key by providing its public half as an argument
581 .Dl $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id host_key.pub
585 is a "key identifier" that is logged by the server when the certificate
586 is used for authentication.
588 Certificates may be limited to be valid for a set of principal (user/host)
590 By default, generated certificates are valid for all users or hosts.
591 To generate a certificate for a specified set of principals:
593 .Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
594 .Dl "$ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub"
596 Additional limitations on the validity and use of user certificates may
597 be specified through certificate options.
598 A certificate option may disable features of the SSH session, may be
599 valid only when presented from particular source addresses or may
600 force the use of a specific command.
601 For a list of valid certificate options, see the documentation for the
605 Finally, certificates may be defined with a validity lifetime.
608 option allows specification of certificate start and end times.
609 A certificate that is presented at a time outside this range will not be
611 By default, certificates have a maximum validity interval.
613 For certificates to be used for user or host authentication, the CA
614 public key must be trusted by
618 Please refer to those manual pages for details.
620 .Bl -tag -width Ds -compact
621 .It Pa ~/.ssh/identity
622 Contains the protocol version 1 RSA authentication identity of the user.
623 This file should not be readable by anyone but the user.
625 specify a passphrase when generating the key; that passphrase will be
626 used to encrypt the private part of this file using 3DES.
627 This file is not automatically accessed by
629 but it is offered as the default file for the private key.
631 will read this file when a login attempt is made.
633 .It Pa ~/.ssh/identity.pub
634 Contains the protocol version 1 RSA public key for authentication.
635 The contents of this file should be added to
636 .Pa ~/.ssh/authorized_keys
638 where the user wishes to log in using RSA authentication.
639 There is no need to keep the contents of this file secret.
642 .It Pa ~/.ssh/id_ecdsa
644 Contains the protocol version 2 DSA, ECDSA or RSA authentication identity of the user.
645 This file should not be readable by anyone but the user.
647 specify a passphrase when generating the key; that passphrase will be
648 used to encrypt the private part of this file using 128-bit AES.
649 This file is not automatically accessed by
651 but it is offered as the default file for the private key.
653 will read this file when a login attempt is made.
655 .It Pa ~/.ssh/id_dsa.pub
656 .It Pa ~/.ssh/id_ecdsa.pub
657 .It Pa ~/.ssh/id_rsa.pub
658 Contains the protocol version 2 DSA, ECDSA or RSA public key for authentication.
659 The contents of this file should be added to
660 .Pa ~/.ssh/authorized_keys
662 where the user wishes to log in using public key authentication.
663 There is no need to keep the contents of this file secret.
666 Contains Diffie-Hellman groups used for DH-GEX.
667 The file format is described in
678 .%T "The Secure Shell (SSH) Public Key File Format"
682 OpenSSH is a derivative of the original and free
683 ssh 1.2.12 release by Tatu Ylonen.
684 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
685 Theo de Raadt and Dug Song
686 removed many bugs, re-added newer features and
688 Markus Friedl contributed the support for SSH
689 protocol versions 1.5 and 2.0.
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