1 .\" $OpenBSD: ssh-keygen.1,v 1.122 2014/03/31 13:39:34 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: March 31 2014 $
43 .Nd authentication key generation, management and conversion
49 .Op Fl t Cm dsa | ecdsa | ed25519 | rsa | rsa1
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
107 .Op Fl J Ar num_lines
108 .Op Fl j Ar start_line
110 .Op Fl W Ar generator
113 .Fl I Ar certificate_identity
115 .Op Fl n Ar principals
117 .Op Fl V Ar validity_interval
118 .Op Fl z Ar serial_number
122 .Op Fl f Ar input_keyfile
129 .Op Fl s Ar ca_public
130 .Op Fl z Ar version_number
139 generates, manages and converts authentication keys for
142 can create RSA keys for use by SSH protocol version 1 and
143 DSA, ECDSA, ED25519 or RSA keys for use by SSH protocol version 2.
144 The type of key to be generated is specified with the
147 If invoked without any arguments,
149 will generate an RSA key for use in SSH protocol 2 connections.
152 is also used to generate groups for use in Diffie-Hellman group
155 .Sx MODULI GENERATION
160 can be used to generate and update Key Revocation Lists, and to test whether
161 given keys have been revoked by one.
163 .Sx KEY REVOCATION LISTS
166 Normally each user wishing to use SSH
167 with public key authentication runs this once to create the authentication
169 .Pa ~/.ssh/identity ,
171 .Pa ~/.ssh/id_ecdsa ,
172 .Pa ~/.ssh/id_ed25519
175 Additionally, the system administrator may use this to generate host keys,
179 Normally this program generates the key and asks for a file in which
180 to store the private key.
181 The public key is stored in a file with the same name but
184 The program also asks for a passphrase.
185 The passphrase may be empty to indicate no passphrase
186 (host keys must have an empty passphrase), or it may be a string of
188 A passphrase is similar to a password, except it can be a phrase with a
189 series of words, punctuation, numbers, whitespace, or any string of
191 Good passphrases are 10-30 characters long, are
192 not simple sentences or otherwise easily guessable (English
193 prose has only 1-2 bits of entropy per character, and provides very bad
194 passphrases), and contain a mix of upper and lowercase letters,
195 numbers, and non-alphanumeric characters.
196 The passphrase can be changed later by using the
200 There is no way to recover a lost passphrase.
201 If the passphrase is lost or forgotten, a new key must be generated
202 and the corresponding public key copied to other machines.
205 there is also a comment field in the key file that is only for
206 convenience to the user to help identify the key.
207 The comment can tell what the key is for, or whatever is useful.
208 The comment is initialized to
210 when the key is created, but can be changed using the
214 After a key is generated, instructions below detail where the keys
215 should be placed to be activated.
217 The options are as follows:
220 For each of the key types (rsa1, rsa, dsa, ecdsa and ed25519)
222 do not exist, generate the host keys with the default key file path,
223 an empty passphrase, default bits for the key type, and default comment.
226 to generate new host keys.
228 When saving a new-format private key (i.e. an ed25519 key or any SSH protocol
231 flag is set), this option specifies the number of KDF (key derivation function)
233 Higher numbers result in slower passphrase verification and increased
234 resistance to brute-force password cracking (should the keys be stolen).
236 When screening DH-GEX candidates (
240 This option specifies the number of primality tests to perform.
242 Show the bubblebabble digest of specified private or public key file.
244 Specifies the number of bits in the key to create.
245 For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
246 Generally, 2048 bits is considered sufficient.
247 DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
250 flag determines the key length by selecting from one of three elliptic
251 curve sizes: 256, 384 or 521 bits.
252 Attempting to use bit lengths other than these three values for ECDSA keys
254 ED25519 keys have a fixed length and the
256 flag will be ignored.
258 Provides a new comment.
260 Requests changing the comment in the private and public key files.
261 This operation is only supported for RSA1 keys.
262 The program will prompt for the file containing the private keys, for
263 the passphrase if the key has one, and for the new comment.
265 Download the RSA public keys provided by the PKCS#11 shared library
267 When used in combination with
269 this option indicates that a CA key resides in a PKCS#11 token (see the
271 section for details).
273 This option will read a private or public OpenSSH key file and
274 print to stdout the key in one of the formats specified by the
277 The default export format is
279 This option allows exporting OpenSSH keys for use by other programs, including
280 several commercial SSH implementations.
282 Search for the specified
286 file, listing any occurrences found.
287 This option is useful to find hashed host names or addresses and may also be
288 used in conjunction with the
290 option to print found keys in a hashed format.
292 Specifies the filename of the key file.
293 .It Fl G Ar output_file
294 Generate candidate primes for DH-GEX.
295 These primes must be screened for
300 Use generic DNS format when printing fingerprint resource records using the
307 This replaces all hostnames and addresses with hashed representations
308 within the specified file; the original content is moved to a file with
310 These hashes may be used normally by
314 but they do not reveal identifying information should the file's contents
316 This option will not modify existing hashed hostnames and is therefore safe
317 to use on files that mix hashed and non-hashed names.
319 When signing a key, create a host certificate instead of a user
324 .It Fl I Ar certificate_identity
325 Specify the key identity when signing a public key.
330 This option will read an unencrypted private (or public) key file
331 in the format specified by the
333 option and print an OpenSSH compatible private
334 (or public) key to stdout.
335 This option allows importing keys from other software, including several
336 commercial SSH implementations.
337 The default import format is
339 .It Fl J Ar num_lines
340 Exit after screening the specified number of lines
341 while performing DH candidate screening using the
344 .It Fl j Ar start_line
345 Start screening at the specified line number
346 while performing DH candidate screening using the
350 Write the last line processed to the file
352 while performing DH candidate screening using the
355 This will be used to skip lines in the input file that have already been
356 processed if the job is restarted.
361 will generate a KRL file at the location specified via the
363 flag that revokes every key or certificate presented on the command line.
364 Keys/certificates to be revoked may be specified by public key file or
365 using the format described in the
366 .Sx KEY REVOCATION LISTS
369 Prints the contents of a certificate.
371 Show fingerprint of specified public key file.
372 Private RSA1 keys are also supported.
375 tries to find the matching public key file and prints its fingerprint.
378 an ASCII art representation of the key is supplied with the fingerprint.
380 Specify the amount of memory to use (in megabytes) when generating
381 candidate moduli for DH-GEX.
382 .It Fl m Ar key_format
383 Specify a key format for the
387 (export) conversion options.
388 The supported key formats are:
390 (RFC 4716/SSH2 public or private key),
392 (PEM PKCS8 public key)
396 The default conversion format is
398 .It Fl N Ar new_passphrase
399 Provides the new passphrase.
400 .It Fl n Ar principals
401 Specify one or more principals (user or host names) to be included in
402 a certificate when signing a key.
403 Multiple principals may be specified, separated by commas.
408 Specify a certificate option when signing a key.
409 This option may be specified multiple times.
413 The options that are valid for user certificates are:
416 Clear all enabled permissions.
417 This is useful for clearing the default set of permissions so permissions may
418 be added individually.
419 .It Ic force-command Ns = Ns Ar command
420 Forces the execution of
422 instead of any shell or command specified by the user when
423 the certificate is used for authentication.
424 .It Ic no-agent-forwarding
427 forwarding (permitted by default).
428 .It Ic no-port-forwarding
429 Disable port forwarding (permitted by default).
431 Disable PTY allocation (permitted by default).
437 (permitted by default).
438 .It Ic no-x11-forwarding
439 Disable X11 forwarding (permitted by default).
440 .It Ic permit-agent-forwarding
444 .It Ic permit-port-forwarding
445 Allows port forwarding.
447 Allows PTY allocation.
448 .It Ic permit-user-rc
453 .It Ic permit-x11-forwarding
454 Allows X11 forwarding.
455 .It Ic source-address Ns = Ns Ar address_list
456 Restrict the source addresses from which the certificate is considered valid.
459 is a comma-separated list of one or more address/netmask pairs in CIDR
463 At present, no options are valid for host keys.
467 to save SSH protocol 2 private keys using the new OpenSSH format rather than
468 the more compatible PEM format.
469 The new format has increased resistance to brute-force password cracking
470 but is not supported by versions of OpenSSH prior to 6.5.
471 Ed25519 keys always use the new private key format.
472 .It Fl P Ar passphrase
473 Provides the (old) passphrase.
475 Requests changing the passphrase of a private key file instead of
476 creating a new private key.
477 The program will prompt for the file
478 containing the private key, for the old passphrase, and twice for the
481 Test whether keys have been revoked in a KRL.
486 Removes all keys belonging to
491 This option is useful to delete hashed hosts (see the
495 Print the SSHFP fingerprint resource record named
497 for the specified public key file.
499 Specify start point (in hex) when generating candidate moduli for DH-GEX.
501 Certify (sign) a public key using the specified CA key.
506 When generating a KRL,
508 specifies a path to a CA public key file used to revoke certificates directly
509 by key ID or serial number.
511 .Sx KEY REVOCATION LISTS
513 .It Fl T Ar output_file
514 Test DH group exchange candidate primes (generated using the
517 .It Fl t Cm dsa | ecdsa | ed25519 | rsa | rsa1
518 Specifies the type of key to create.
519 The possible values are
521 for protocol version 1 and
527 for protocol version 2.
532 keys listed via the command line are added to the existing KRL rather than
533 a new KRL being created.
534 .It Fl V Ar validity_interval
535 Specify a validity interval when signing a certificate.
536 A validity interval may consist of a single time, indicating that the
537 certificate is valid beginning now and expiring at that time, or may consist
538 of two times separated by a colon to indicate an explicit time interval.
539 The start time may be specified as a date in YYYYMMDD format, a time
540 in YYYYMMDDHHMMSS format or a relative time (to the current time) consisting
541 of a minus sign followed by a relative time in the format described in the
542 TIME FORMATS section of
544 The end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMMSS time or
545 a relative time starting with a plus character.
549 (valid from now to 52 weeks and one day from now),
551 (valid from four weeks ago to four weeks from now),
552 .Dq 20100101123000:20110101123000
553 (valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
555 (valid from yesterday to midnight, January 1st, 2011).
560 to print debugging messages about its progress.
561 This is helpful for debugging moduli generation.
564 options increase the verbosity.
566 .It Fl W Ar generator
567 Specify desired generator when testing candidate moduli for DH-GEX.
569 This option will read a private
570 OpenSSH format file and print an OpenSSH public key to stdout.
571 .It Fl z Ar serial_number
572 Specifies a serial number to be embedded in the certificate to distinguish
573 this certificate from others from the same CA.
574 The default serial number is zero.
576 When generating a KRL, the
578 flag is used to specify a KRL version number.
580 .Sh MODULI GENERATION
582 may be used to generate groups for the Diffie-Hellman Group Exchange
584 Generating these groups is a two-step process: first, candidate
585 primes are generated using a fast, but memory intensive process.
586 These candidate primes are then tested for suitability (a CPU-intensive
589 Generation of primes is performed using the
592 The desired length of the primes may be specified by the
597 .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
599 By default, the search for primes begins at a random point in the
600 desired length range.
601 This may be overridden using the
603 option, which specifies a different start point (in hex).
605 Once a set of candidates have been generated, they must be screened for
607 This may be performed using the
612 will read candidates from standard input (or a file specified using the
617 .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
619 By default, each candidate will be subjected to 100 primality tests.
620 This may be overridden using the
623 The DH generator value will be chosen automatically for the
624 prime under consideration.
625 If a specific generator is desired, it may be requested using the
628 Valid generator values are 2, 3, and 5.
630 Screened DH groups may be installed in
632 It is important that this file contains moduli of a range of bit lengths and
633 that both ends of a connection share common moduli.
636 supports signing of keys to produce certificates that may be used for
637 user or host authentication.
638 Certificates consist of a public key, some identity information, zero or
639 more principal (user or host) names and a set of options that
640 are signed by a Certification Authority (CA) key.
641 Clients or servers may then trust only the CA key and verify its signature
642 on a certificate rather than trusting many user/host keys.
643 Note that OpenSSH certificates are a different, and much simpler, format to
644 the X.509 certificates used in
648 supports two types of certificates: user and host.
649 User certificates authenticate users to servers, whereas host certificates
650 authenticate server hosts to users.
651 To generate a user certificate:
653 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
655 The resultant certificate will be placed in
656 .Pa /path/to/user_key-cert.pub .
657 A host certificate requires the
661 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
663 The host certificate will be output to
664 .Pa /path/to/host_key-cert.pub .
666 It is possible to sign using a CA key stored in a PKCS#11 token by
667 providing the token library using
669 and identifying the CA key by providing its public half as an argument
673 .Dl $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id host_key.pub
677 is a "key identifier" that is logged by the server when the certificate
678 is used for authentication.
680 Certificates may be limited to be valid for a set of principal (user/host)
682 By default, generated certificates are valid for all users or hosts.
683 To generate a certificate for a specified set of principals:
685 .Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
686 .Dl "$ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub"
688 Additional limitations on the validity and use of user certificates may
689 be specified through certificate options.
690 A certificate option may disable features of the SSH session, may be
691 valid only when presented from particular source addresses or may
692 force the use of a specific command.
693 For a list of valid certificate options, see the documentation for the
697 Finally, certificates may be defined with a validity lifetime.
700 option allows specification of certificate start and end times.
701 A certificate that is presented at a time outside this range will not be
703 By default, certificates are valid from
705 Epoch to the distant future.
707 For certificates to be used for user or host authentication, the CA
708 public key must be trusted by
712 Please refer to those manual pages for details.
713 .Sh KEY REVOCATION LISTS
715 is able to manage OpenSSH format Key Revocation Lists (KRLs).
716 These binary files specify keys or certificates to be revoked using a
717 compact format, taking as little as one bit per certificate if they are being
718 revoked by serial number.
720 KRLs may be generated using the
723 This option reads one or more files from the command line and generates a new
725 The files may either contain a KRL specification (see below) or public keys,
727 Plain public keys are revoked by listing their hash or contents in the KRL and
728 certificates revoked by serial number or key ID (if the serial is zero or
731 Revoking keys using a KRL specification offers explicit control over the
732 types of record used to revoke keys and may be used to directly revoke
733 certificates by serial number or key ID without having the complete original
735 A KRL specification consists of lines containing one of the following directives
736 followed by a colon and some directive-specific information.
738 .It Cm serial : Ar serial_number Ns Op - Ns Ar serial_number
739 Revokes a certificate with the specified serial number.
740 Serial numbers are 64-bit values, not including zero and may be expressed
741 in decimal, hex or octal.
742 If two serial numbers are specified separated by a hyphen, then the range
743 of serial numbers including and between each is revoked.
744 The CA key must have been specified on the
746 command line using the
749 .It Cm id : Ar key_id
750 Revokes a certificate with the specified key ID string.
751 The CA key must have been specified on the
753 command line using the
756 .It Cm key : Ar public_key
757 Revokes the specified key.
758 If a certificate is listed, then it is revoked as a plain public key.
759 .It Cm sha1 : Ar public_key
760 Revokes the specified key by its SHA1 hash.
763 KRLs may be updated using the
767 When this option is specified, keys listed via the command line are merged into
768 the KRL, adding to those already there.
770 It is also possible, given a KRL, to test whether it revokes a particular key
774 flag will query an existing KRL, testing each key specified on the commandline.
775 If any key listed on the command line has been revoked (or an error encountered)
778 will exit with a non-zero exit status.
779 A zero exit status will only be returned if no key was revoked.
781 .Bl -tag -width Ds -compact
782 .It Pa ~/.ssh/identity
783 Contains the protocol version 1 RSA authentication identity of the user.
784 This file should not be readable by anyone but the user.
786 specify a passphrase when generating the key; that passphrase will be
787 used to encrypt the private part of this file using 3DES.
788 This file is not automatically accessed by
790 but it is offered as the default file for the private key.
792 will read this file when a login attempt is made.
794 .It Pa ~/.ssh/identity.pub
795 Contains the protocol version 1 RSA public key for authentication.
796 The contents of this file should be added to
797 .Pa ~/.ssh/authorized_keys
799 where the user wishes to log in using RSA authentication.
800 There is no need to keep the contents of this file secret.
803 .It Pa ~/.ssh/id_ecdsa
804 .It Pa ~/.ssh/id_ed25519
806 Contains the protocol version 2 DSA, ECDSA, ED25519 or RSA
807 authentication identity of the user.
808 This file should not be readable by anyone but the user.
810 specify a passphrase when generating the key; that passphrase will be
811 used to encrypt the private part of this file using 128-bit AES.
812 This file is not automatically accessed by
814 but it is offered as the default file for the private key.
816 will read this file when a login attempt is made.
818 .It Pa ~/.ssh/id_dsa.pub
819 .It Pa ~/.ssh/id_ecdsa.pub
820 .It Pa ~/.ssh/id_ed25519.pub
821 .It Pa ~/.ssh/id_rsa.pub
822 Contains the protocol version 2 DSA, ECDSA, ED25519 or RSA
823 public key for authentication.
824 The contents of this file should be added to
825 .Pa ~/.ssh/authorized_keys
827 where the user wishes to log in using public key authentication.
828 There is no need to keep the contents of this file secret.
831 Contains Diffie-Hellman groups used for DH-GEX.
832 The file format is described in
843 .%T "The Secure Shell (SSH) Public Key File Format"
847 OpenSSH is a derivative of the original and free
848 ssh 1.2.12 release by Tatu Ylonen.
849 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
850 Theo de Raadt and Dug Song
851 removed many bugs, re-added newer features and
853 Markus Friedl contributed the support for SSH
854 protocol versions 1.5 and 2.0.
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