1 .\" $OpenBSD: ssh-keygen.1,v 1.101 2010/10/28 18:33:28 jmc Exp $
3 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 .\" All rights reserved
7 .\" As far as I am concerned, the code I have written for this software
8 .\" can be used freely for any purpose. Any derived versions of this
9 .\" software must be clearly marked as such, and if the derived work is
10 .\" incompatible with the protocol description in the RFC file, it must be
11 .\" called by a name other than "ssh" or "Secure Shell".
14 .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
15 .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
16 .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
18 .\" Redistribution and use in source and binary forms, with or without
19 .\" modification, are permitted provided that the following conditions
21 .\" 1. Redistributions of source code must retain the above copyright
22 .\" notice, this list of conditions and the following disclaimer.
23 .\" 2. Redistributions in binary form must reproduce the above copyright
24 .\" notice, this list of conditions and the following disclaimer in the
25 .\" documentation and/or other materials provided with the distribution.
27 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
28 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
29 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
30 .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
31 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
32 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
33 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
34 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
35 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
36 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
38 .Dd $Mdocdate: October 28 2010 $
43 .Nd authentication key generation, management and conversion
50 .Op Fl N Ar new_passphrase
52 .Op Fl f Ar output_keyfile
55 .Op Fl P Ar old_passphrase
56 .Op Fl N Ar new_passphrase
60 .Op Fl m Ar key_format
61 .Op Fl f Ar input_keyfile
64 .Op Fl m Ar key_format
65 .Op Fl f Ar input_keyfile
68 .Op Fl f Ar input_keyfile
71 .Op Fl P Ar passphrase
76 .Op Fl f Ar input_keyfile
79 .Op Fl f Ar input_keyfile
84 .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
101 .Op Fl S Ar start_point
106 .Op Fl a Ar num_trials
107 .Op Fl W Ar generator
110 .Fl I Ar certificate_identity
112 .Op Fl n Ar principals
114 .Op Fl V Ar validity_interval
115 .Op Fl z Ar serial_number
119 .Op Fl f Ar input_keyfile
123 generates, manages and converts authentication keys for
126 can create RSA keys for use by SSH protocol version 1 and DSA, ECDSA or RSA
127 keys for use by SSH protocol version 2.
128 The type of key to be generated is specified with the
131 If invoked without any arguments,
133 will generate an RSA key for use in SSH protocol 2 connections.
136 is also used to generate groups for use in Diffie-Hellman group
139 .Sx MODULI GENERATION
142 Normally each user wishing to use SSH
143 with public key authentication runs this once to create the authentication
145 .Pa ~/.ssh/identity ,
146 .Pa ~/.ssh/id_ecdsa ,
150 Additionally, the system administrator may use this to generate host keys,
154 Normally this program generates the key and asks for a file in which
155 to store the private key.
156 The public key is stored in a file with the same name but
159 The program also asks for a passphrase.
160 The passphrase may be empty to indicate no passphrase
161 (host keys must have an empty passphrase), or it may be a string of
163 A passphrase is similar to a password, except it can be a phrase with a
164 series of words, punctuation, numbers, whitespace, or any string of
166 Good passphrases are 10-30 characters long, are
167 not simple sentences or otherwise easily guessable (English
168 prose has only 1-2 bits of entropy per character, and provides very bad
169 passphrases), and contain a mix of upper and lowercase letters,
170 numbers, and non-alphanumeric characters.
171 The passphrase can be changed later by using the
175 There is no way to recover a lost passphrase.
177 lost or forgotten, a new key must be generated and copied to the
178 corresponding public key to other machines.
181 there is also a comment field in the key file that is only for
182 convenience to the user to help identify the key.
183 The comment can tell what the key is for, or whatever is useful.
184 The comment is initialized to
186 when the key is created, but can be changed using the
190 After a key is generated, instructions below detail where the keys
191 should be placed to be activated.
193 The options are as follows:
196 Specifies the number of primality tests to perform when screening DH-GEX
201 Show the bubblebabble digest of specified private or public key file.
203 Specifies the number of bits in the key to create.
204 For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
205 Generally, 2048 bits is considered sufficient.
206 DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
208 Provides a new comment.
210 Requests changing the comment in the private and public key files.
211 This operation is only supported for RSA1 keys.
212 The program will prompt for the file containing the private keys, for
213 the passphrase if the key has one, and for the new comment.
215 Download the RSA public keys provided by the PKCS#11 shared library
217 When used in combination with
219 this option indicates that a CA key resides in a PKCS#11 token (see the
221 section for details).
223 This option will read a private or public OpenSSH key file and
224 print to stdout the key in one of the formats specified by the
227 The default export format is
229 This option allows exporting OpenSSH keys for use by other programs, including
230 several commercial SSH implementations.
232 Search for the specified
236 file, listing any occurrences found.
237 This option is useful to find hashed host names or addresses and may also be
238 used in conjunction with the
240 option to print found keys in a hashed format.
242 Specifies the filename of the key file.
243 .It Fl G Ar output_file
244 Generate candidate primes for DH-GEX.
245 These primes must be screened for
250 Use generic DNS format when printing fingerprint resource records using the
257 This replaces all hostnames and addresses with hashed representations
258 within the specified file; the original content is moved to a file with
260 These hashes may be used normally by
264 but they do not reveal identifying information should the file's contents
266 This option will not modify existing hashed hostnames and is therefore safe
267 to use on files that mix hashed and non-hashed names.
269 When signing a key, create a host certificate instead of a user
274 .It Fl I Ar certificate_identity
275 Specify the key identity when signing a public key.
280 This option will read an unencrypted private (or public) key file
281 in the format specified by the
283 option and print an OpenSSH compatible private
284 (or public) key to stdout.
285 This option allows importing keys from other software, including several
286 commercial SSH implementations.
287 The default import format is
290 Prints the contents of a certificate.
292 Show fingerprint of specified public key file.
293 Private RSA1 keys are also supported.
296 tries to find the matching public key file and prints its fingerprint.
299 an ASCII art representation of the key is supplied with the fingerprint.
301 Specify the amount of memory to use (in megabytes) when generating
302 candidate moduli for DH-GEX.
303 .It Fl m Ar key_format
304 Specify a key format for the
308 (export) conversion options.
309 The supported key formats are:
311 (RFC 4716/SSH2 public or private key),
313 (PEM PKCS8 public key)
317 The default conversion format is
319 .It Fl N Ar new_passphrase
320 Provides the new passphrase.
321 .It Fl n Ar principals
322 Specify one or more principals (user or host names) to be included in
323 a certificate when signing a key.
324 Multiple principals may be specified, separated by commas.
329 Specify a certificate option when signing a key.
330 This option may be specified multiple times.
334 The options that are valid for user certificates are:
337 Clear all enabled permissions.
338 This is useful for clearing the default set of permissions so permissions may
339 be added individually.
340 .It Ic force-command Ns = Ns Ar command
341 Forces the execution of
343 instead of any shell or command specified by the user when
344 the certificate is used for authentication.
345 .It Ic no-agent-forwarding
348 forwarding (permitted by default).
349 .It Ic no-port-forwarding
350 Disable port forwarding (permitted by default).
352 Disable PTY allocation (permitted by default).
358 (permitted by default).
359 .It Ic no-x11-forwarding
360 Disable X11 forwarding (permitted by default).
361 .It Ic permit-agent-forwarding
365 .It Ic permit-port-forwarding
366 Allows port forwarding.
368 Allows PTY allocation.
369 .It Ic permit-user-rc
374 .It Ic permit-x11-forwarding
375 Allows X11 forwarding.
376 .It Ic source-address Ns = Ns Ar address_list
377 Restrict the source addresses from which the certificate is considered valid.
380 is a comma-separated list of one or more address/netmask pairs in CIDR
384 At present, no options are valid for host keys.
385 .It Fl P Ar passphrase
386 Provides the (old) passphrase.
388 Requests changing the passphrase of a private key file instead of
389 creating a new private key.
390 The program will prompt for the file
391 containing the private key, for the old passphrase, and twice for the
398 when creating a new key.
400 Removes all keys belonging to
405 This option is useful to delete hashed hosts (see the
409 Print the SSHFP fingerprint resource record named
411 for the specified public key file.
413 Specify start point (in hex) when generating candidate moduli for DH-GEX.
415 Certify (sign) a public key using the specified CA key.
419 .It Fl T Ar output_file
420 Test DH group exchange candidate primes (generated using the
424 Specifies the type of key to create.
425 The possible values are
427 for protocol version 1 and
432 for protocol version 2.
433 .It Fl V Ar validity_interval
434 Specify a validity interval when signing a certificate.
435 A validity interval may consist of a single time, indicating that the
436 certificate is valid beginning now and expiring at that time, or may consist
437 of two times separated by a colon to indicate an explicit time interval.
438 The start time may be specified as a date in YYYYMMDD format, a time
439 in YYYYMMDDHHMMSS format or a relative time (to the current time) consisting
440 of a minus sign followed by a relative time in the format described in the
444 The end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMMSS time or
445 a relative time starting with a plus character.
449 (valid from now to 52 weeks and one day from now),
451 (valid from four weeks ago to four weeks from now),
452 .Dq 20100101123000:20110101123000
453 (valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
455 (valid from yesterday to midnight, January 1st, 2011).
460 to print debugging messages about its progress.
461 This is helpful for debugging moduli generation.
464 options increase the verbosity.
466 .It Fl W Ar generator
467 Specify desired generator when testing candidate moduli for DH-GEX.
469 This option will read a private
470 OpenSSH format file and print an OpenSSH public key to stdout.
471 .It Fl z Ar serial_number
472 Specifies a serial number to be embedded in the certificate to distinguish
473 this certificate from others from the same CA.
474 The default serial number is zero.
476 .Sh MODULI GENERATION
478 may be used to generate groups for the Diffie-Hellman Group Exchange
480 Generating these groups is a two-step process: first, candidate
481 primes are generated using a fast, but memory intensive process.
482 These candidate primes are then tested for suitability (a CPU-intensive
485 Generation of primes is performed using the
488 The desired length of the primes may be specified by the
493 .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
495 By default, the search for primes begins at a random point in the
496 desired length range.
497 This may be overridden using the
499 option, which specifies a different start point (in hex).
501 Once a set of candidates have been generated, they must be tested for
503 This may be performed using the
508 will read candidates from standard input (or a file specified using the
513 .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
515 By default, each candidate will be subjected to 100 primality tests.
516 This may be overridden using the
519 The DH generator value will be chosen automatically for the
520 prime under consideration.
521 If a specific generator is desired, it may be requested using the
524 Valid generator values are 2, 3, and 5.
526 Screened DH groups may be installed in
528 It is important that this file contains moduli of a range of bit lengths and
529 that both ends of a connection share common moduli.
532 supports signing of keys to produce certificates that may be used for
533 user or host authentication.
534 Certificates consist of a public key, some identity information, zero or
535 more principal (user or host) names and a set of options that
536 are signed by a Certification Authority (CA) key.
537 Clients or servers may then trust only the CA key and verify its signature
538 on a certificate rather than trusting many user/host keys.
539 Note that OpenSSH certificates are a different, and much simpler, format to
540 the X.509 certificates used in
544 supports two types of certificates: user and host.
545 User certificates authenticate users to servers, whereas host certificates
546 authenticate server hosts to users.
547 To generate a user certificate:
549 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
551 The resultant certificate will be placed in
552 .Pa /path/to/user_key-cert.pub .
553 A host certificate requires the
557 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
559 The host certificate will be output to
560 .Pa /path/to/host_key-cert.pub .
562 It is possible to sign using a CA key stored in a PKCS#11 token by
563 providing the token library using
565 and identifying the CA key by providing its public half as an argument
569 .Dl $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id host_key.pub
573 is a "key identifier" that is logged by the server when the certificate
574 is used for authentication.
576 Certificates may be limited to be valid for a set of principal (user/host)
578 By default, generated certificates are valid for all users or hosts.
579 To generate a certificate for a specified set of principals:
581 .Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
582 .Dl "$ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub"
584 Additional limitations on the validity and use of user certificates may
585 be specified through certificate options.
586 A certificate option may disable features of the SSH session, may be
587 valid only when presented from particular source addresses or may
588 force the use of a specific command.
589 For a list of valid certificate options, see the documentation for the
593 Finally, certificates may be defined with a validity lifetime.
596 option allows specification of certificate start and end times.
597 A certificate that is presented at a time outside this range will not be
599 By default, certificates have a maximum validity interval.
601 For certificates to be used for user or host authentication, the CA
602 public key must be trusted by
606 Please refer to those manual pages for details.
608 .Bl -tag -width Ds -compact
609 .It Pa ~/.ssh/identity
610 Contains the protocol version 1 RSA authentication identity of the user.
611 This file should not be readable by anyone but the user.
613 specify a passphrase when generating the key; that passphrase will be
614 used to encrypt the private part of this file using 3DES.
615 This file is not automatically accessed by
617 but it is offered as the default file for the private key.
619 will read this file when a login attempt is made.
621 .It Pa ~/.ssh/identity.pub
622 Contains the protocol version 1 RSA public key for authentication.
623 The contents of this file should be added to
624 .Pa ~/.ssh/authorized_keys
626 where the user wishes to log in using RSA authentication.
627 There is no need to keep the contents of this file secret.
630 .It Pa ~/.ssh/id_ecdsa
632 Contains the protocol version 2 DSA, ECDSA or RSA authentication identity of the user.
633 This file should not be readable by anyone but the user.
635 specify a passphrase when generating the key; that passphrase will be
636 used to encrypt the private part of this file using 128-bit AES.
637 This file is not automatically accessed by
639 but it is offered as the default file for the private key.
641 will read this file when a login attempt is made.
643 .It Pa ~/.ssh/id_dsa.pub
644 .It Pa ~/.ssh/id_ecdsa.pub
645 .It Pa ~/.ssh/id_rsa.pub
646 Contains the protocol version 2 DSA, ECDSA or RSA public key for authentication.
647 The contents of this file should be added to
648 .Pa ~/.ssh/authorized_keys
650 where the user wishes to log in using public key authentication.
651 There is no need to keep the contents of this file secret.
654 Contains Diffie-Hellman groups used for DH-GEX.
655 The file format is described in
666 .%T "The Secure Shell (SSH) Public Key File Format"
670 OpenSSH is a derivative of the original and free
671 ssh 1.2.12 release by Tatu Ylonen.
672 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
673 Theo de Raadt and Dug Song
674 removed many bugs, re-added newer features and
676 Markus Friedl contributed the support for SSH
677 protocol versions 1.5 and 2.0.
projects / openssh.git / blob