1 .\" $OpenBSD: ssh-keygen.1,v 1.144 2017/07/08 18:32:54 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: July 8 2017 $
43 .Nd authentication key generation, management and conversion
49 .Op Fl t Cm dsa | ecdsa | ed25519 | rsa
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
77 .Op Fl E Ar fingerprint_hash
78 .Op Fl f Ar input_keyfile
81 .Op Fl f Ar input_keyfile
86 .Op Fl f Ar known_hosts_file
90 .Op Fl f Ar known_hosts_file
93 .Op Fl f Ar known_hosts_file
96 .Op Fl f Ar input_keyfile
103 .Op Fl S Ar start_point
109 .Op Fl J Ar num_lines
110 .Op Fl j Ar start_line
112 .Op Fl W Ar generator
115 .Fl I Ar certificate_identity
118 .Op Fl D Ar pkcs11_provider
119 .Op Fl n Ar principals
121 .Op Fl V Ar validity_interval
122 .Op Fl z Ar serial_number
126 .Op Fl f Ar input_keyfile
129 .Op Fl f Ar prefix_path
134 .Op Fl s Ar ca_public
135 .Op Fl z Ar version_number
144 generates, manages and converts authentication keys for
147 can create keys for use by SSH protocol version 2.
149 The type of key to be generated is specified with the
152 If invoked without any arguments,
154 will generate an RSA key.
157 is also used to generate groups for use in Diffie-Hellman group
160 .Sx MODULI GENERATION
165 can be used to generate and update Key Revocation Lists, and to test whether
166 given keys have been revoked by one.
168 .Sx KEY REVOCATION LISTS
171 Normally each user wishing to use SSH
172 with public key authentication runs this once to create the authentication
175 .Pa ~/.ssh/id_ecdsa ,
176 .Pa ~/.ssh/id_ed25519
179 Additionally, the system administrator may use this to generate host keys,
183 Normally this program generates the key and asks for a file in which
184 to store the private key.
185 The public key is stored in a file with the same name but
188 The program also asks for a passphrase.
189 The passphrase may be empty to indicate no passphrase
190 (host keys must have an empty passphrase), or it may be a string of
192 A passphrase is similar to a password, except it can be a phrase with a
193 series of words, punctuation, numbers, whitespace, or any string of
195 Good passphrases are 10-30 characters long, are
196 not simple sentences or otherwise easily guessable (English
197 prose has only 1-2 bits of entropy per character, and provides very bad
198 passphrases), and contain a mix of upper and lowercase letters,
199 numbers, and non-alphanumeric characters.
200 The passphrase can be changed later by using the
204 There is no way to recover a lost passphrase.
205 If the passphrase is lost or forgotten, a new key must be generated
206 and the corresponding public key copied to other machines.
208 For keys stored in the newer OpenSSH format,
209 there is also a comment field in the key file that is only for
210 convenience to the user to help identify the key.
211 The comment can tell what the key is for, or whatever is useful.
212 The comment is initialized to
214 when the key is created, but can be changed using the
218 After a key is generated, instructions below detail where the keys
219 should be placed to be activated.
221 The options are as follows:
224 For each of the key types (rsa, dsa, ecdsa and ed25519)
226 do not exist, generate the host keys with the default key file path,
227 an empty passphrase, default bits for the key type, and default comment.
230 has also been specified, its argument is used as a prefix to the
231 default path for the resulting host key files.
234 to generate new host keys.
236 When saving a new-format private key (i.e. an ed25519 key or when the
238 flag is set), this option specifies the number of KDF (key derivation function)
240 Higher numbers result in slower passphrase verification and increased
241 resistance to brute-force password cracking (should the keys be stolen).
243 When screening DH-GEX candidates (using the
246 This option specifies the number of primality tests to perform.
248 Show the bubblebabble digest of specified private or public key file.
250 Specifies the number of bits in the key to create.
251 For RSA keys, the minimum size is 1024 bits and the default is 2048 bits.
252 Generally, 2048 bits is considered sufficient.
253 DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
256 flag determines the key length by selecting from one of three elliptic
257 curve sizes: 256, 384 or 521 bits.
258 Attempting to use bit lengths other than these three values for ECDSA keys
260 Ed25519 keys have a fixed length and the
262 flag will be ignored.
264 Provides a new comment.
266 Requests changing the comment in the private and public key files.
267 This operation is only supported for keys stored in the
268 newer OpenSSH format.
269 The program will prompt for the file containing the private keys, for
270 the passphrase if the key has one, and for the new comment.
272 Download the RSA public keys provided by the PKCS#11 shared library
274 When used in combination with
276 this option indicates that a CA key resides in a PKCS#11 token (see the
278 section for details).
279 .It Fl E Ar fingerprint_hash
280 Specifies the hash algorithm used when displaying key fingerprints.
288 This option will read a private or public OpenSSH key file and
289 print to stdout the key in one of the formats specified by the
292 The default export format is
294 This option allows exporting OpenSSH keys for use by other programs, including
295 several commercial SSH implementations.
297 Search for the specified
301 file, listing any occurrences found.
302 This option is useful to find hashed host names or addresses and may also be
303 used in conjunction with the
305 option to print found keys in a hashed format.
307 Specifies the filename of the key file.
308 .It Fl G Ar output_file
309 Generate candidate primes for DH-GEX.
310 These primes must be screened for
315 Use generic DNS format when printing fingerprint resource records using the
322 This replaces all hostnames and addresses with hashed representations
323 within the specified file; the original content is moved to a file with
325 These hashes may be used normally by
329 but they do not reveal identifying information should the file's contents
331 This option will not modify existing hashed hostnames and is therefore safe
332 to use on files that mix hashed and non-hashed names.
334 When signing a key, create a host certificate instead of a user
339 .It Fl I Ar certificate_identity
340 Specify the key identity when signing a public key.
345 This option will read an unencrypted private (or public) key file
346 in the format specified by the
348 option and print an OpenSSH compatible private
349 (or public) key to stdout.
350 This option allows importing keys from other software, including several
351 commercial SSH implementations.
352 The default import format is
354 .It Fl J Ar num_lines
355 Exit after screening the specified number of lines
356 while performing DH candidate screening using the
359 .It Fl j Ar start_line
360 Start screening at the specified line number
361 while performing DH candidate screening using the
365 Write the last line processed to the file
367 while performing DH candidate screening using the
370 This will be used to skip lines in the input file that have already been
371 processed if the job is restarted.
376 will generate a KRL file at the location specified via the
378 flag that revokes every key or certificate presented on the command line.
379 Keys/certificates to be revoked may be specified by public key file or
380 using the format described in the
381 .Sx KEY REVOCATION LISTS
384 Prints the contents of one or more certificates.
386 Show fingerprint of specified public key file.
389 tries to find the matching public key file and prints its fingerprint.
392 a visual ASCII art representation of the key is supplied with the
395 Specify the amount of memory to use (in megabytes) when generating
396 candidate moduli for DH-GEX.
397 .It Fl m Ar key_format
398 Specify a key format for the
402 (export) conversion options.
403 The supported key formats are:
405 (RFC 4716/SSH2 public or private key),
407 (PEM PKCS8 public key)
411 The default conversion format is
413 .It Fl N Ar new_passphrase
414 Provides the new passphrase.
415 .It Fl n Ar principals
416 Specify one or more principals (user or host names) to be included in
417 a certificate when signing a key.
418 Multiple principals may be specified, separated by commas.
423 Specify a certificate option when signing a key.
424 This option may be specified multiple times.
427 section for further details.
428 The options that are valid for user certificates are:
430 .Bl -tag -width Ds -compact
432 Clear all enabled permissions.
433 This is useful for clearing the default set of permissions so permissions may
434 be added individually.
436 .It Ic critical : Ns Ar name Ns Op Ns = Ns Ar contents
437 .It Ic extension : Ns Ar name Ns Op Ns = Ns Ar contents
438 Includes an arbitrary certificate critical option or extension.
441 should include a domain suffix, e.g.\&
442 .Dq name@example.com .
445 is specified then it is included as the contents of the extension/option
446 encoded as a string, otherwise the extension/option is created with no
447 contents (usually indicating a flag).
448 Extensions may be ignored by a client or server that does not recognise them,
449 whereas unknown critical options will cause the certificate to be refused.
451 At present, no standard options are valid for host keys.
453 .It Ic force-command Ns = Ns Ar command
454 Forces the execution of
456 instead of any shell or command specified by the user when
457 the certificate is used for authentication.
459 .It Ic no-agent-forwarding
462 forwarding (permitted by default).
464 .It Ic no-port-forwarding
465 Disable port forwarding (permitted by default).
468 Disable PTY allocation (permitted by default).
475 (permitted by default).
477 .It Ic no-x11-forwarding
478 Disable X11 forwarding (permitted by default).
480 .It Ic permit-agent-forwarding
485 .It Ic permit-port-forwarding
486 Allows port forwarding.
489 Allows PTY allocation.
491 .It Ic permit-user-rc
497 .It Ic permit-x11-forwarding
498 Allows X11 forwarding.
500 .It Ic source-address Ns = Ns Ar address_list
501 Restrict the source addresses from which the certificate is considered valid.
504 is a comma-separated list of one or more address/netmask pairs in CIDR
510 to save private keys using the new OpenSSH format rather than
511 the more compatible PEM format.
512 The new format has increased resistance to brute-force password cracking
513 but is not supported by versions of OpenSSH prior to 6.5.
514 Ed25519 keys always use the new private key format.
515 .It Fl P Ar passphrase
516 Provides the (old) passphrase.
518 Requests changing the passphrase of a private key file instead of
519 creating a new private key.
520 The program will prompt for the file
521 containing the private key, for the old passphrase, and twice for the
524 Test whether keys have been revoked in a KRL.
529 Removes all keys belonging to
534 This option is useful to delete hashed hosts (see the
538 Print the SSHFP fingerprint resource record named
540 for the specified public key file.
542 Specify start point (in hex) when generating candidate moduli for DH-GEX.
544 Certify (sign) a public key using the specified CA key.
549 When generating a KRL,
551 specifies a path to a CA public key file used to revoke certificates directly
552 by key ID or serial number.
554 .Sx KEY REVOCATION LISTS
556 .It Fl T Ar output_file
557 Test DH group exchange candidate primes (generated using the
560 .It Fl t Cm dsa | ecdsa | ed25519 | rsa
561 Specifies the type of key to create.
562 The possible values are
569 When used in combination with
571 this option indicates that a CA key resides in a
575 section for more information.
580 keys listed via the command line are added to the existing KRL rather than
581 a new KRL being created.
582 .It Fl V Ar validity_interval
583 Specify a validity interval when signing a certificate.
584 A validity interval may consist of a single time, indicating that the
585 certificate is valid beginning now and expiring at that time, or may consist
586 of two times separated by a colon to indicate an explicit time interval.
587 The start time may be specified as a date in YYYYMMDD format, a time
588 in YYYYMMDDHHMMSS format or a relative time (to the current time) consisting
589 of a minus sign followed by a relative time in the format described in the
590 TIME FORMATS section of
592 The end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMMSS time or
593 a relative time starting with a plus character.
597 (valid from now to 52 weeks and one day from now),
599 (valid from four weeks ago to four weeks from now),
600 .Dq 20100101123000:20110101123000
601 (valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
603 (valid from yesterday to midnight, January 1st, 2011).
608 to print debugging messages about its progress.
609 This is helpful for debugging moduli generation.
612 options increase the verbosity.
614 .It Fl W Ar generator
615 Specify desired generator when testing candidate moduli for DH-GEX.
617 This option will read a private
618 OpenSSH format file and print an OpenSSH public key to stdout.
619 .It Fl z Ar serial_number
620 Specifies a serial number to be embedded in the certificate to distinguish
621 this certificate from others from the same CA.
622 The default serial number is zero.
624 When generating a KRL, the
626 flag is used to specify a KRL version number.
628 .Sh MODULI GENERATION
630 may be used to generate groups for the Diffie-Hellman Group Exchange
632 Generating these groups is a two-step process: first, candidate
633 primes are generated using a fast, but memory intensive process.
634 These candidate primes are then tested for suitability (a CPU-intensive
637 Generation of primes is performed using the
640 The desired length of the primes may be specified by the
645 .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
647 By default, the search for primes begins at a random point in the
648 desired length range.
649 This may be overridden using the
651 option, which specifies a different start point (in hex).
653 Once a set of candidates have been generated, they must be screened for
655 This may be performed using the
660 will read candidates from standard input (or a file specified using the
665 .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
667 By default, each candidate will be subjected to 100 primality tests.
668 This may be overridden using the
671 The DH generator value will be chosen automatically for the
672 prime under consideration.
673 If a specific generator is desired, it may be requested using the
676 Valid generator values are 2, 3, and 5.
678 Screened DH groups may be installed in
680 It is important that this file contains moduli of a range of bit lengths and
681 that both ends of a connection share common moduli.
684 supports signing of keys to produce certificates that may be used for
685 user or host authentication.
686 Certificates consist of a public key, some identity information, zero or
687 more principal (user or host) names and a set of options that
688 are signed by a Certification Authority (CA) key.
689 Clients or servers may then trust only the CA key and verify its signature
690 on a certificate rather than trusting many user/host keys.
691 Note that OpenSSH certificates are a different, and much simpler, format to
692 the X.509 certificates used in
696 supports two types of certificates: user and host.
697 User certificates authenticate users to servers, whereas host certificates
698 authenticate server hosts to users.
699 To generate a user certificate:
701 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
703 The resultant certificate will be placed in
704 .Pa /path/to/user_key-cert.pub .
705 A host certificate requires the
709 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
711 The host certificate will be output to
712 .Pa /path/to/host_key-cert.pub .
714 It is possible to sign using a CA key stored in a PKCS#11 token by
715 providing the token library using
717 and identifying the CA key by providing its public half as an argument
721 .Dl $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub
723 Similarly, it is possible for the CA key to be hosted in a
725 This is indicated by the
727 flag and, again, the CA key must be identified by its public half.
729 .Dl $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub
733 is a "key identifier" that is logged by the server when the certificate
734 is used for authentication.
736 Certificates may be limited to be valid for a set of principal (user/host)
738 By default, generated certificates are valid for all users or hosts.
739 To generate a certificate for a specified set of principals:
741 .Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
742 .Dl "$ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub"
744 Additional limitations on the validity and use of user certificates may
745 be specified through certificate options.
746 A certificate option may disable features of the SSH session, may be
747 valid only when presented from particular source addresses or may
748 force the use of a specific command.
749 For a list of valid certificate options, see the documentation for the
753 Finally, certificates may be defined with a validity lifetime.
756 option allows specification of certificate start and end times.
757 A certificate that is presented at a time outside this range will not be
759 By default, certificates are valid from
761 Epoch to the distant future.
763 For certificates to be used for user or host authentication, the CA
764 public key must be trusted by
768 Please refer to those manual pages for details.
769 .Sh KEY REVOCATION LISTS
771 is able to manage OpenSSH format Key Revocation Lists (KRLs).
772 These binary files specify keys or certificates to be revoked using a
773 compact format, taking as little as one bit per certificate if they are being
774 revoked by serial number.
776 KRLs may be generated using the
779 This option reads one or more files from the command line and generates a new
781 The files may either contain a KRL specification (see below) or public keys,
783 Plain public keys are revoked by listing their hash or contents in the KRL and
784 certificates revoked by serial number or key ID (if the serial is zero or
787 Revoking keys using a KRL specification offers explicit control over the
788 types of record used to revoke keys and may be used to directly revoke
789 certificates by serial number or key ID without having the complete original
791 A KRL specification consists of lines containing one of the following directives
792 followed by a colon and some directive-specific information.
794 .It Cm serial : Ar serial_number Ns Op - Ns Ar serial_number
795 Revokes a certificate with the specified serial number.
796 Serial numbers are 64-bit values, not including zero and may be expressed
797 in decimal, hex or octal.
798 If two serial numbers are specified separated by a hyphen, then the range
799 of serial numbers including and between each is revoked.
800 The CA key must have been specified on the
802 command line using the
805 .It Cm id : Ar key_id
806 Revokes a certificate with the specified key ID string.
807 The CA key must have been specified on the
809 command line using the
812 .It Cm key : Ar public_key
813 Revokes the specified key.
814 If a certificate is listed, then it is revoked as a plain public key.
815 .It Cm sha1 : Ar public_key
816 Revokes the specified key by its SHA1 hash.
819 KRLs may be updated using the
823 When this option is specified, keys listed via the command line are merged into
824 the KRL, adding to those already there.
826 It is also possible, given a KRL, to test whether it revokes a particular key
830 flag will query an existing KRL, testing each key specified on the command line.
831 If any key listed on the command line has been revoked (or an error encountered)
834 will exit with a non-zero exit status.
835 A zero exit status will only be returned if no key was revoked.
837 .Bl -tag -width Ds -compact
839 .It Pa ~/.ssh/id_ecdsa
840 .It Pa ~/.ssh/id_ed25519
842 Contains the DSA, ECDSA, Ed25519 or RSA
843 authentication identity of the user.
844 This file should not be readable by anyone but the user.
846 specify a passphrase when generating the key; that passphrase will be
847 used to encrypt the private part of this file using 128-bit AES.
848 This file is not automatically accessed by
850 but it is offered as the default file for the private key.
852 will read this file when a login attempt is made.
854 .It Pa ~/.ssh/id_dsa.pub
855 .It Pa ~/.ssh/id_ecdsa.pub
856 .It Pa ~/.ssh/id_ed25519.pub
857 .It Pa ~/.ssh/id_rsa.pub
858 Contains the DSA, ECDSA, Ed25519 or RSA
859 public key for authentication.
860 The contents of this file should be added to
861 .Pa ~/.ssh/authorized_keys
863 where the user wishes to log in using public key authentication.
864 There is no need to keep the contents of this file secret.
867 Contains Diffie-Hellman groups used for DH-GEX.
868 The file format is described in
879 .%T "The Secure Shell (SSH) Public Key File Format"
883 OpenSSH is a derivative of the original and free
884 ssh 1.2.12 release by Tatu Ylonen.
885 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
886 Theo de Raadt and Dug Song
887 removed many bugs, re-added newer features and
889 Markus Friedl contributed the support for SSH
890 protocol versions 1.5 and 2.0.
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