1 .\" $OpenBSD: ssh-keygen.1,v 1.106 2011/04/13 04:09:37 djm 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: April 13 2011 $
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
125 generates, manages and converts authentication keys for
128 can create RSA keys for use by SSH protocol version 1 and DSA, ECDSA or RSA
129 keys for use by SSH protocol version 2.
130 The type of key to be generated is specified with the
133 If invoked without any arguments,
135 will generate an RSA key for use in SSH protocol 2 connections.
138 is also used to generate groups for use in Diffie-Hellman group
141 .Sx MODULI GENERATION
144 Normally each user wishing to use SSH
145 with public key authentication runs this once to create the authentication
147 .Pa ~/.ssh/identity ,
148 .Pa ~/.ssh/id_ecdsa ,
152 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.
176 If the passphrase is lost or forgotten, a new key must be generated
177 and the corresponding public key copied to other machines.
180 there is also a comment field in the key file that is only for
181 convenience to the user to help identify the key.
182 The comment can tell what the key is for, or whatever is useful.
183 The comment is initialized to
185 when the key is created, but can be changed using the
189 After a key is generated, instructions below detail where the keys
190 should be placed to be activated.
192 The options are as follows:
195 For each of the key types (rsa1, rsa, dsa and ecdsa) for which host keys
196 do not exist, generate the host keys with the default key file path,
197 an empty passphrase, default bits for the key type, and default comment.
198 This is used by system administration scripts to generate new host keys.
200 Specifies the number of primality tests to perform when screening DH-GEX
205 Show the bubblebabble digest of specified private or public key file.
207 Specifies the number of bits in the key to create.
208 For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
209 Generally, 2048 bits is considered sufficient.
210 DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
213 flag determines they key length by selecting from one of three elliptic
214 curve sizes: 256, 384 or 521 bits.
215 Attempting to use bit lengths other than these three values for ECDSA keys
218 Provides a new comment.
220 Requests changing the comment in the private and public key files.
221 This operation is only supported for RSA1 keys.
222 The program will prompt for the file containing the private keys, for
223 the passphrase if the key has one, and for the new comment.
225 Download the RSA public keys provided by the PKCS#11 shared library
227 When used in combination with
229 this option indicates that a CA key resides in a PKCS#11 token (see the
231 section for details).
233 This option will read a private or public OpenSSH key file and
234 print to stdout the key in one of the formats specified by the
237 The default export format is
239 This option allows exporting OpenSSH keys for use by other programs, including
240 several commercial SSH implementations.
242 Search for the specified
246 file, listing any occurrences found.
247 This option is useful to find hashed host names or addresses and may also be
248 used in conjunction with the
250 option to print found keys in a hashed format.
252 Specifies the filename of the key file.
253 .It Fl G Ar output_file
254 Generate candidate primes for DH-GEX.
255 These primes must be screened for
260 Use generic DNS format when printing fingerprint resource records using the
267 This replaces all hostnames and addresses with hashed representations
268 within the specified file; the original content is moved to a file with
270 These hashes may be used normally by
274 but they do not reveal identifying information should the file's contents
276 This option will not modify existing hashed hostnames and is therefore safe
277 to use on files that mix hashed and non-hashed names.
279 When signing a key, create a host certificate instead of a user
284 .It Fl I Ar certificate_identity
285 Specify the key identity when signing a public key.
290 This option will read an unencrypted private (or public) key file
291 in the format specified by the
293 option and print an OpenSSH compatible private
294 (or public) key to stdout.
295 This option allows importing keys from other software, including several
296 commercial SSH implementations.
297 The default import format is
300 Prints the contents of a certificate.
302 Show fingerprint of specified public key file.
303 Private RSA1 keys are also supported.
306 tries to find the matching public key file and prints its fingerprint.
309 an ASCII art representation of the key is supplied with the fingerprint.
311 Specify the amount of memory to use (in megabytes) when generating
312 candidate moduli for DH-GEX.
313 .It Fl m Ar key_format
314 Specify a key format for the
318 (export) conversion options.
319 The supported key formats are:
321 (RFC 4716/SSH2 public or private key),
323 (PEM PKCS8 public key)
327 The default conversion format is
329 .It Fl N Ar new_passphrase
330 Provides the new passphrase.
331 .It Fl n Ar principals
332 Specify one or more principals (user or host names) to be included in
333 a certificate when signing a key.
334 Multiple principals may be specified, separated by commas.
339 Specify a certificate option when signing a key.
340 This option may be specified multiple times.
344 The options that are valid for user certificates are:
347 Clear all enabled permissions.
348 This is useful for clearing the default set of permissions so permissions may
349 be added individually.
350 .It Ic force-command Ns = Ns Ar command
351 Forces the execution of
353 instead of any shell or command specified by the user when
354 the certificate is used for authentication.
355 .It Ic no-agent-forwarding
358 forwarding (permitted by default).
359 .It Ic no-port-forwarding
360 Disable port forwarding (permitted by default).
362 Disable PTY allocation (permitted by default).
368 (permitted by default).
369 .It Ic no-x11-forwarding
370 Disable X11 forwarding (permitted by default).
371 .It Ic permit-agent-forwarding
375 .It Ic permit-port-forwarding
376 Allows port forwarding.
378 Allows PTY allocation.
379 .It Ic permit-user-rc
384 .It Ic permit-x11-forwarding
385 Allows X11 forwarding.
386 .It Ic source-address Ns = Ns Ar address_list
387 Restrict the source addresses from which the certificate is considered valid.
390 is a comma-separated list of one or more address/netmask pairs in CIDR
394 At present, no options are valid for host keys.
395 .It Fl P Ar passphrase
396 Provides the (old) passphrase.
398 Requests changing the passphrase of a private key file instead of
399 creating a new private key.
400 The program will prompt for the file
401 containing the private key, for the old passphrase, and twice for the
407 Removes all keys belonging to
412 This option is useful to delete hashed hosts (see the
416 Print the SSHFP fingerprint resource record named
418 for the specified public key file.
420 Specify start point (in hex) when generating candidate moduli for DH-GEX.
422 Certify (sign) a public key using the specified CA key.
426 .It Fl T Ar output_file
427 Test DH group exchange candidate primes (generated using the
431 Specifies the type of key to create.
432 The possible values are
434 for protocol version 1 and
439 for protocol version 2.
440 .It Fl V Ar validity_interval
441 Specify a validity interval when signing a certificate.
442 A validity interval may consist of a single time, indicating that the
443 certificate is valid beginning now and expiring at that time, or may consist
444 of two times separated by a colon to indicate an explicit time interval.
445 The start time may be specified as a date in YYYYMMDD format, a time
446 in YYYYMMDDHHMMSS format or a relative time (to the current time) consisting
447 of a minus sign followed by a relative time in the format described in the
451 The end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMMSS time or
452 a relative time starting with a plus character.
456 (valid from now to 52 weeks and one day from now),
458 (valid from four weeks ago to four weeks from now),
459 .Dq 20100101123000:20110101123000
460 (valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
462 (valid from yesterday to midnight, January 1st, 2011).
467 to print debugging messages about its progress.
468 This is helpful for debugging moduli generation.
471 options increase the verbosity.
473 .It Fl W Ar generator
474 Specify desired generator when testing candidate moduli for DH-GEX.
476 This option will read a private
477 OpenSSH format file and print an OpenSSH public key to stdout.
478 .It Fl z Ar serial_number
479 Specifies a serial number to be embedded in the certificate to distinguish
480 this certificate from others from the same CA.
481 The default serial number is zero.
483 .Sh MODULI GENERATION
485 may be used to generate groups for the Diffie-Hellman Group Exchange
487 Generating these groups is a two-step process: first, candidate
488 primes are generated using a fast, but memory intensive process.
489 These candidate primes are then tested for suitability (a CPU-intensive
492 Generation of primes is performed using the
495 The desired length of the primes may be specified by the
500 .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
502 By default, the search for primes begins at a random point in the
503 desired length range.
504 This may be overridden using the
506 option, which specifies a different start point (in hex).
508 Once a set of candidates have been generated, they must be tested for
510 This may be performed using the
515 will read candidates from standard input (or a file specified using the
520 .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
522 By default, each candidate will be subjected to 100 primality tests.
523 This may be overridden using the
526 The DH generator value will be chosen automatically for the
527 prime under consideration.
528 If a specific generator is desired, it may be requested using the
531 Valid generator values are 2, 3, and 5.
533 Screened DH groups may be installed in
534 .Pa /etc/ssh/moduli .
535 It is important that this file contains moduli of a range of bit lengths and
536 that both ends of a connection share common moduli.
539 supports signing of keys to produce certificates that may be used for
540 user or host authentication.
541 Certificates consist of a public key, some identity information, zero or
542 more principal (user or host) names and a set of options that
543 are signed by a Certification Authority (CA) key.
544 Clients or servers may then trust only the CA key and verify its signature
545 on a certificate rather than trusting many user/host keys.
546 Note that OpenSSH certificates are a different, and much simpler, format to
547 the X.509 certificates used in
551 supports two types of certificates: user and host.
552 User certificates authenticate users to servers, whereas host certificates
553 authenticate server hosts to users.
554 To generate a user certificate:
556 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
558 The resultant certificate will be placed in
559 .Pa /path/to/user_key-cert.pub .
560 A host certificate requires the
564 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
566 The host certificate will be output to
567 .Pa /path/to/host_key-cert.pub .
569 It is possible to sign using a CA key stored in a PKCS#11 token by
570 providing the token library using
572 and identifying the CA key by providing its public half as an argument
576 .Dl $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id host_key.pub
580 is a "key identifier" that is logged by the server when the certificate
581 is used for authentication.
583 Certificates may be limited to be valid for a set of principal (user/host)
585 By default, generated certificates are valid for all users or hosts.
586 To generate a certificate for a specified set of principals:
588 .Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
589 .Dl "$ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub"
591 Additional limitations on the validity and use of user certificates may
592 be specified through certificate options.
593 A certificate option may disable features of the SSH session, may be
594 valid only when presented from particular source addresses or may
595 force the use of a specific command.
596 For a list of valid certificate options, see the documentation for the
600 Finally, certificates may be defined with a validity lifetime.
603 option allows specification of certificate start and end times.
604 A certificate that is presented at a time outside this range will not be
606 By default, certificates have a maximum validity interval.
608 For certificates to be used for user or host authentication, the CA
609 public key must be trusted by
613 Please refer to those manual pages for details.
615 .Bl -tag -width Ds -compact
616 .It Pa ~/.ssh/identity
617 Contains the protocol version 1 RSA authentication identity of the user.
618 This file should not be readable by anyone but the user.
620 specify a passphrase when generating the key; that passphrase will be
621 used to encrypt the private part of this file using 3DES.
622 This file is not automatically accessed by
624 but it is offered as the default file for the private key.
626 will read this file when a login attempt is made.
628 .It Pa ~/.ssh/identity.pub
629 Contains the protocol version 1 RSA public key for authentication.
630 The contents of this file should be added to
631 .Pa ~/.ssh/authorized_keys
633 where the user wishes to log in using RSA authentication.
634 There is no need to keep the contents of this file secret.
637 .It Pa ~/.ssh/id_ecdsa
639 Contains the protocol version 2 DSA, ECDSA or RSA authentication identity of the user.
640 This file should not be readable by anyone but the user.
642 specify a passphrase when generating the key; that passphrase will be
643 used to encrypt the private part of this file using 128-bit AES.
644 This file is not automatically accessed by
646 but it is offered as the default file for the private key.
648 will read this file when a login attempt is made.
650 .It Pa ~/.ssh/id_dsa.pub
651 .It Pa ~/.ssh/id_ecdsa.pub
652 .It Pa ~/.ssh/id_rsa.pub
653 Contains the protocol version 2 DSA, ECDSA or RSA public key for authentication.
654 The contents of this file should be added to
655 .Pa ~/.ssh/authorized_keys
657 where the user wishes to log in using public key authentication.
658 There is no need to keep the contents of this file secret.
660 .It Pa /etc/ssh/moduli
661 Contains Diffie-Hellman groups used for DH-GEX.
662 The file format is described in
674 .%T "The Secure Shell (SSH) Public Key File Format"
678 OpenSSH is a derivative of the original and free
679 ssh 1.2.12 release by Tatu Ylonen.
680 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
681 Theo de Raadt and Dug Song
682 removed many bugs, re-added newer features and
684 Markus Friedl contributed the support for SSH
685 protocol versions 1.5 and 2.0.
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