1 .\" $OpenBSD: ssh-keygen.1,v 1.120 2014/02/05 20:13:25 naddy 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
108 .Op Fl J Ar num_lines
109 .Op Fl j Ar start_line
111 .Op Fl W Ar generator
114 .Fl I Ar certificate_identity
116 .Op Fl n Ar principals
118 .Op Fl V Ar validity_interval
119 .Op Fl z Ar serial_number
123 .Op Fl f Ar input_keyfile
130 .Op Fl s Ar ca_public
131 .Op Fl z Ar version_number
140 generates, manages and converts authentication keys for
143 can create RSA keys for use by SSH protocol version 1 and
144 DSA, ECDSA, ED25519 or RSA keys for use by SSH protocol version 2.
145 The type of key to be generated is specified with the
148 If invoked without any arguments,
150 will generate an RSA key for use in SSH protocol 2 connections.
153 is also used to generate groups for use in Diffie-Hellman group
156 .Sx MODULI GENERATION
161 can be used to generate and update Key Revocation Lists, and to test whether
162 given keys have been revoked by one.
164 .Sx KEY REVOCATION LISTS
167 Normally each user wishing to use SSH
168 with public key authentication runs this once to create the authentication
170 .Pa ~/.ssh/identity ,
172 .Pa ~/.ssh/id_ecdsa ,
173 .Pa ~/.ssh/id_ed25519
176 Additionally, the system administrator may use this to generate host keys,
180 Normally this program generates the key and asks for a file in which
181 to store the private key.
182 The public key is stored in a file with the same name but
185 The program also asks for a passphrase.
186 The passphrase may be empty to indicate no passphrase
187 (host keys must have an empty passphrase), or it may be a string of
189 A passphrase is similar to a password, except it can be a phrase with a
190 series of words, punctuation, numbers, whitespace, or any string of
192 Good passphrases are 10-30 characters long, are
193 not simple sentences or otherwise easily guessable (English
194 prose has only 1-2 bits of entropy per character, and provides very bad
195 passphrases), and contain a mix of upper and lowercase letters,
196 numbers, and non-alphanumeric characters.
197 The passphrase can be changed later by using the
201 There is no way to recover a lost passphrase.
202 If the passphrase is lost or forgotten, a new key must be generated
203 and the corresponding public key copied to other machines.
206 there is also a comment field in the key file that is only for
207 convenience to the user to help identify the key.
208 The comment can tell what the key is for, or whatever is useful.
209 The comment is initialized to
211 when the key is created, but can be changed using the
215 After a key is generated, instructions below detail where the keys
216 should be placed to be activated.
218 The options are as follows:
221 For each of the key types (rsa1, rsa, dsa, ecdsa and ed25519)
223 do not exist, generate the host keys with the default key file path,
224 an empty passphrase, default bits for the key type, and default comment.
227 to generate new host keys.
229 When saving a new-format private key (i.e. an ed25519 key or any SSH protocol
232 flag is set), this option specifies the number of KDF (key derivation function)
234 Higher numbers result in slower passphrase verification and increased
235 resistance to brute-force password cracking (should the keys be stolen).
237 When screening DH-GEX candidates (
241 This option specifies the number of primality tests to perform.
243 Show the bubblebabble digest of specified private or public key file.
245 Specifies the number of bits in the key to create.
246 For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
247 Generally, 2048 bits is considered sufficient.
248 DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
251 flag determines the key length by selecting from one of three elliptic
252 curve sizes: 256, 384 or 521 bits.
253 Attempting to use bit lengths other than these three values for ECDSA keys
255 ED25519 keys have a fixed length and the
257 flag will be ignored.
259 Provides a new comment.
261 Requests changing the comment in the private and public key files.
262 This operation is only supported for RSA1 keys.
263 The program will prompt for the file containing the private keys, for
264 the passphrase if the key has one, and for the new comment.
266 Download the RSA public keys provided by the PKCS#11 shared library
268 When used in combination with
270 this option indicates that a CA key resides in a PKCS#11 token (see the
272 section for details).
274 This option will read a private or public OpenSSH key file and
275 print to stdout the key in one of the formats specified by the
278 The default export format is
280 This option allows exporting OpenSSH keys for use by other programs, including
281 several commercial SSH implementations.
283 Search for the specified
287 file, listing any occurrences found.
288 This option is useful to find hashed host names or addresses and may also be
289 used in conjunction with the
291 option to print found keys in a hashed format.
293 Specifies the filename of the key file.
294 .It Fl G Ar output_file
295 Generate candidate primes for DH-GEX.
296 These primes must be screened for
301 Use generic DNS format when printing fingerprint resource records using the
308 This replaces all hostnames and addresses with hashed representations
309 within the specified file; the original content is moved to a file with
311 These hashes may be used normally by
315 but they do not reveal identifying information should the file's contents
317 This option will not modify existing hashed hostnames and is therefore safe
318 to use on files that mix hashed and non-hashed names.
320 When signing a key, create a host certificate instead of a user
325 .It Fl I Ar certificate_identity
326 Specify the key identity when signing a public key.
331 This option will read an unencrypted private (or public) key file
332 in the format specified by the
334 option and print an OpenSSH compatible private
335 (or public) key to stdout.
336 .It Fl J Ar num_lines
337 Exit after screening the specified number of lines
338 while performing DH candidate screening using the
341 .It Fl j Ar start_line
342 Start screening at the specified line number
343 while performing DH candidate screening using the
347 Write the last line processed to the file
349 while performing DH candidate screening using the
352 This will be used to skip lines in the input file that have already been
353 processed if the job is restarted.
354 This option allows importing keys from other software, including several
355 commercial SSH implementations.
356 The default import format is
362 will generate a KRL file at the location specified via the
364 flag that revokes every key or certificate presented on the command line.
365 Keys/certificates to be revoked may be specified by public key file or
366 using the format described in the
367 .Sx KEY REVOCATION LISTS
370 Prints the contents of a certificate.
372 Show fingerprint of specified public key file.
373 Private RSA1 keys are also supported.
376 tries to find the matching public key file and prints its fingerprint.
379 an ASCII art representation of the key is supplied with the fingerprint.
381 Specify the amount of memory to use (in megabytes) when generating
382 candidate moduli for DH-GEX.
383 .It Fl m Ar key_format
384 Specify a key format for the
388 (export) conversion options.
389 The supported key formats are:
391 (RFC 4716/SSH2 public or private key),
393 (PEM PKCS8 public key)
397 The default conversion format is
399 .It Fl N Ar new_passphrase
400 Provides the new passphrase.
401 .It Fl n Ar principals
402 Specify one or more principals (user or host names) to be included in
403 a certificate when signing a key.
404 Multiple principals may be specified, separated by commas.
409 Specify a certificate option when signing a key.
410 This option may be specified multiple times.
414 The options that are valid for user certificates are:
417 Clear all enabled permissions.
418 This is useful for clearing the default set of permissions so permissions may
419 be added individually.
420 .It Ic force-command Ns = Ns Ar command
421 Forces the execution of
423 instead of any shell or command specified by the user when
424 the certificate is used for authentication.
425 .It Ic no-agent-forwarding
428 forwarding (permitted by default).
429 .It Ic no-port-forwarding
430 Disable port forwarding (permitted by default).
432 Disable PTY allocation (permitted by default).
438 (permitted by default).
439 .It Ic no-x11-forwarding
440 Disable X11 forwarding (permitted by default).
441 .It Ic permit-agent-forwarding
445 .It Ic permit-port-forwarding
446 Allows port forwarding.
448 Allows PTY allocation.
449 .It Ic permit-user-rc
454 .It Ic permit-x11-forwarding
455 Allows X11 forwarding.
456 .It Ic source-address Ns = Ns Ar address_list
457 Restrict the source addresses from which the certificate is considered valid.
460 is a comma-separated list of one or more address/netmask pairs in CIDR
464 At present, no options are valid for host keys.
468 to save SSH protocol 2 private keys using the new OpenSSH format rather than
469 the more compatible PEM format.
470 The new format has increased resistance to brute-force password cracking
471 but is not supported by versions of OpenSSH prior to 6.5.
472 Ed25519 keys always use the new private key format.
473 .It Fl P Ar passphrase
474 Provides the (old) passphrase.
476 Requests changing the passphrase of a private key file instead of
477 creating a new private key.
478 The program will prompt for the file
479 containing the private key, for the old passphrase, and twice for the
482 Test whether keys have been revoked in a KRL.
487 Removes all keys belonging to
492 This option is useful to delete hashed hosts (see the
496 Print the SSHFP fingerprint resource record named
498 for the specified public key file.
500 Specify start point (in hex) when generating candidate moduli for DH-GEX.
502 Certify (sign) a public key using the specified CA key.
507 When generating a KRL,
509 specifies a path to a CA public key file used to revoke certificates directly
510 by key ID or serial number.
512 .Sx KEY REVOCATION LISTS
514 .It Fl T Ar output_file
515 Test DH group exchange candidate primes (generated using the
519 Specifies the type of key to create.
520 The possible values are
522 for protocol version 1 and
528 for protocol version 2.
533 keys listed via the command line are added to the existing KRL rather than
534 a new KRL being created.
535 .It Fl V Ar validity_interval
536 Specify a validity interval when signing a certificate.
537 A validity interval may consist of a single time, indicating that the
538 certificate is valid beginning now and expiring at that time, or may consist
539 of two times separated by a colon to indicate an explicit time interval.
540 The start time may be specified as a date in YYYYMMDD format, a time
541 in YYYYMMDDHHMMSS format or a relative time (to the current time) consisting
542 of a minus sign followed by a relative time in the format described in the
543 TIME FORMATS section of
545 The end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMMSS time or
546 a relative time starting with a plus character.
550 (valid from now to 52 weeks and one day from now),
552 (valid from four weeks ago to four weeks from now),
553 .Dq 20100101123000:20110101123000
554 (valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
556 (valid from yesterday to midnight, January 1st, 2011).
561 to print debugging messages about its progress.
562 This is helpful for debugging moduli generation.
565 options increase the verbosity.
567 .It Fl W Ar generator
568 Specify desired generator when testing candidate moduli for DH-GEX.
570 This option will read a private
571 OpenSSH format file and print an OpenSSH public key to stdout.
572 .It Fl z Ar serial_number
573 Specifies a serial number to be embedded in the certificate to distinguish
574 this certificate from others from the same CA.
575 The default serial number is zero.
577 When generating a KRL, the
579 flag is used to specify a KRL version number.
581 .Sh MODULI GENERATION
583 may be used to generate groups for the Diffie-Hellman Group Exchange
585 Generating these groups is a two-step process: first, candidate
586 primes are generated using a fast, but memory intensive process.
587 These candidate primes are then tested for suitability (a CPU-intensive
590 Generation of primes is performed using the
593 The desired length of the primes may be specified by the
598 .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
600 By default, the search for primes begins at a random point in the
601 desired length range.
602 This may be overridden using the
604 option, which specifies a different start point (in hex).
606 Once a set of candidates have been generated, they must be screened for
608 This may be performed using the
613 will read candidates from standard input (or a file specified using the
618 .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
620 By default, each candidate will be subjected to 100 primality tests.
621 This may be overridden using the
624 The DH generator value will be chosen automatically for the
625 prime under consideration.
626 If a specific generator is desired, it may be requested using the
629 Valid generator values are 2, 3, and 5.
631 Screened DH groups may be installed in
633 It is important that this file contains moduli of a range of bit lengths and
634 that both ends of a connection share common moduli.
637 supports signing of keys to produce certificates that may be used for
638 user or host authentication.
639 Certificates consist of a public key, some identity information, zero or
640 more principal (user or host) names and a set of options that
641 are signed by a Certification Authority (CA) key.
642 Clients or servers may then trust only the CA key and verify its signature
643 on a certificate rather than trusting many user/host keys.
644 Note that OpenSSH certificates are a different, and much simpler, format to
645 the X.509 certificates used in
649 supports two types of certificates: user and host.
650 User certificates authenticate users to servers, whereas host certificates
651 authenticate server hosts to users.
652 To generate a user certificate:
654 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
656 The resultant certificate will be placed in
657 .Pa /path/to/user_key-cert.pub .
658 A host certificate requires the
662 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
664 The host certificate will be output to
665 .Pa /path/to/host_key-cert.pub .
667 It is possible to sign using a CA key stored in a PKCS#11 token by
668 providing the token library using
670 and identifying the CA key by providing its public half as an argument
674 .Dl $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id host_key.pub
678 is a "key identifier" that is logged by the server when the certificate
679 is used for authentication.
681 Certificates may be limited to be valid for a set of principal (user/host)
683 By default, generated certificates are valid for all users or hosts.
684 To generate a certificate for a specified set of principals:
686 .Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
687 .Dl "$ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub"
689 Additional limitations on the validity and use of user certificates may
690 be specified through certificate options.
691 A certificate option may disable features of the SSH session, may be
692 valid only when presented from particular source addresses or may
693 force the use of a specific command.
694 For a list of valid certificate options, see the documentation for the
698 Finally, certificates may be defined with a validity lifetime.
701 option allows specification of certificate start and end times.
702 A certificate that is presented at a time outside this range will not be
704 By default, certificates are valid from
706 Epoch to the distant future.
708 For certificates to be used for user or host authentication, the CA
709 public key must be trusted by
713 Please refer to those manual pages for details.
714 .Sh KEY REVOCATION LISTS
716 is able to manage OpenSSH format Key Revocation Lists (KRLs).
717 These binary files specify keys or certificates to be revoked using a
718 compact format, taking as little as one bit per certificate if they are being
719 revoked by serial number.
721 KRLs may be generated using the
724 This option reads one or more files from the command line and generates a new
726 The files may either contain a KRL specification (see below) or public keys,
728 Plain public keys are revoked by listing their hash or contents in the KRL and
729 certificates revoked by serial number or key ID (if the serial is zero or
732 Revoking keys using a KRL specification offers explicit control over the
733 types of record used to revoke keys and may be used to directly revoke
734 certificates by serial number or key ID without having the complete original
736 A KRL specification consists of lines containing one of the following directives
737 followed by a colon and some directive-specific information.
739 .It Cm serial : Ar serial_number Ns Op - Ns Ar serial_number
740 Revokes a certificate with the specified serial number.
741 Serial numbers are 64-bit values, not including zero and may be expressed
742 in decimal, hex or octal.
743 If two serial numbers are specified separated by a hyphen, then the range
744 of serial numbers including and between each is revoked.
745 The CA key must have been specified on the
747 command line using the
750 .It Cm id : Ar key_id
751 Revokes a certificate with the specified key ID string.
752 The CA key must have been specified on the
754 command line using the
757 .It Cm key : Ar public_key
758 Revokes the specified key.
759 If a certificate is listed, then it is revoked as a plain public key.
760 .It Cm sha1 : Ar public_key
761 Revokes the specified key by its SHA1 hash.
764 KRLs may be updated using the
768 When this option is specified, keys listed via the command line are merged into
769 the KRL, adding to those already there.
771 It is also possible, given a KRL, to test whether it revokes a particular key
775 flag will query an existing KRL, testing each key specified on the commandline.
776 If any key listed on the command line has been revoked (or an error encountered)
779 will exit with a non-zero exit status.
780 A zero exit status will only be returned if no key was revoked.
782 .Bl -tag -width Ds -compact
783 .It Pa ~/.ssh/identity
784 Contains the protocol version 1 RSA authentication identity of the user.
785 This file should not be readable by anyone but the user.
787 specify a passphrase when generating the key; that passphrase will be
788 used to encrypt the private part of this file using 3DES.
789 This file is not automatically accessed by
791 but it is offered as the default file for the private key.
793 will read this file when a login attempt is made.
795 .It Pa ~/.ssh/identity.pub
796 Contains the protocol version 1 RSA public key for authentication.
797 The contents of this file should be added to
798 .Pa ~/.ssh/authorized_keys
800 where the user wishes to log in using RSA authentication.
801 There is no need to keep the contents of this file secret.
804 .It Pa ~/.ssh/id_ecdsa
805 .It Pa ~/.ssh/id_ed25519
807 Contains the protocol version 2 DSA, ECDSA, ED25519 or RSA
808 authentication identity of the user.
809 This file should not be readable by anyone but the user.
811 specify a passphrase when generating the key; that passphrase will be
812 used to encrypt the private part of this file using 128-bit AES.
813 This file is not automatically accessed by
815 but it is offered as the default file for the private key.
817 will read this file when a login attempt is made.
819 .It Pa ~/.ssh/id_dsa.pub
820 .It Pa ~/.ssh/id_ecdsa.pub
821 .It Pa ~/.ssh/id_ed25519.pub
822 .It Pa ~/.ssh/id_rsa.pub
823 Contains the protocol version 2 DSA, ECDSA, ED25519 or RSA
824 public key for authentication.
825 The contents of this file should be added to
826 .Pa ~/.ssh/authorized_keys
828 where the user wishes to log in using public key authentication.
829 There is no need to keep the contents of this file secret.
832 Contains Diffie-Hellman groups used for DH-GEX.
833 The file format is described in
844 .%T "The Secure Shell (SSH) Public Key File Format"
848 OpenSSH is a derivative of the original and free
849 ssh 1.2.12 release by Tatu Ylonen.
850 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
851 Theo de Raadt and Dug Song
852 removed many bugs, re-added newer features and
854 Markus Friedl contributed the support for SSH
855 protocol versions 1.5 and 2.0.
projects / FreeBSD / releng / 10.2.git / blob