1 .\" $OpenBSD: ssh-keygen.1,v 1.157 2019/03/05 16:17:12 naddy 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 5 2019 $
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
56 .Op Fl P Ar old_passphrase
57 .Op Fl N Ar new_passphrase
62 .Op Fl m Ar key_format
63 .Op Fl f Ar input_keyfile
66 .Op Fl m Ar key_format
67 .Op Fl f Ar input_keyfile
70 .Op Fl f Ar input_keyfile
73 .Op Fl P Ar passphrase
79 .Op Fl E Ar fingerprint_hash
80 .Op Fl f Ar input_keyfile
83 .Op Fl f Ar input_keyfile
88 .Op Fl f Ar known_hosts_file
92 .Op Fl f Ar known_hosts_file
95 .Op Fl f Ar known_hosts_file
98 .Op Fl f Ar input_keyfile
105 .Op Fl S Ar start_point
111 .Op Fl J Ar num_lines
112 .Op Fl j Ar start_line
114 .Op Fl W Ar generator
117 .Fl I Ar certificate_identity
120 .Op Fl D Ar pkcs11_provider
121 .Op Fl n Ar principals
123 .Op Fl V Ar validity_interval
124 .Op Fl z Ar serial_number
128 .Op Fl f Ar input_keyfile
131 .Op Fl f Ar prefix_path
136 .Op Fl s Ar ca_public
137 .Op Fl z Ar version_number
146 generates, manages and converts authentication keys for
149 can create keys for use by SSH protocol version 2.
151 The type of key to be generated is specified with the
154 If invoked without any arguments,
156 will generate an RSA key.
159 is also used to generate groups for use in Diffie-Hellman group
162 .Sx MODULI GENERATION
167 can be used to generate and update Key Revocation Lists, and to test whether
168 given keys have been revoked by one.
170 .Sx KEY REVOCATION LISTS
173 Normally each user wishing to use SSH
174 with public key authentication runs this once to create the authentication
177 .Pa ~/.ssh/id_ecdsa ,
178 .Pa ~/.ssh/id_ed25519
181 Additionally, the system administrator may use this to generate host keys,
185 Normally this program generates the key and asks for a file in which
186 to store the private key.
187 The public key is stored in a file with the same name but
190 The program also asks for a passphrase.
191 The passphrase may be empty to indicate no passphrase
192 (host keys must have an empty passphrase), or it may be a string of
194 A passphrase is similar to a password, except it can be a phrase with a
195 series of words, punctuation, numbers, whitespace, or any string of
197 Good passphrases are 10-30 characters long, are
198 not simple sentences or otherwise easily guessable (English
199 prose has only 1-2 bits of entropy per character, and provides very bad
200 passphrases), and contain a mix of upper and lowercase letters,
201 numbers, and non-alphanumeric characters.
202 The passphrase can be changed later by using the
206 There is no way to recover a lost passphrase.
207 If the passphrase is lost or forgotten, a new key must be generated
208 and the corresponding public key copied to other machines.
211 will by default write keys in an OpenSSH-specific format.
212 This format is preferred as it offers better protection for
213 keys at rest as well as allowing storage of key comments within
214 the private key file itself.
215 The key comment may be useful to help identify the key.
216 The comment is initialized to
218 when the key is created, but can be changed using the
222 It is still possible for
224 to write the previously-used PEM format private keys using the
227 This may be used when generating new keys, and existing new-format
228 keys may be converted using this option in conjunction with the
230 (change passphrase) flag.
232 After a key is generated, instructions below detail where the keys
233 should be placed to be activated.
235 The options are as follows:
238 For each of the key types (rsa, dsa, ecdsa and ed25519)
240 do not exist, generate the host keys with the default key file path,
241 an empty passphrase, default bits for the key type, and default comment.
244 has also been specified, its argument is used as a prefix to the
245 default path for the resulting host key files.
248 to generate new host keys.
250 When saving a private key this option specifies the number of KDF
251 (key derivation function) rounds used.
252 Higher numbers result in slower passphrase verification and increased
253 resistance to brute-force password cracking (should the keys be stolen).
255 When screening DH-GEX candidates (using the
258 This option specifies the number of primality tests to perform.
260 Show the bubblebabble digest of specified private or public key file.
262 Specifies the number of bits in the key to create.
263 For RSA keys, the minimum size is 1024 bits and the default is 2048 bits.
264 Generally, 2048 bits is considered sufficient.
265 DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
268 flag determines the key length by selecting from one of three elliptic
269 curve sizes: 256, 384 or 521 bits.
270 Attempting to use bit lengths other than these three values for ECDSA keys
272 Ed25519 keys have a fixed length and the
274 flag will be ignored.
276 Provides a new comment.
278 Requests changing the comment in the private and public key files.
279 The program will prompt for the file containing the private keys, for
280 the passphrase if the key has one, and for the new comment.
282 Download the public keys provided by the PKCS#11 shared library
284 When used in combination with
286 this option indicates that a CA key resides in a PKCS#11 token (see the
288 section for details).
289 .It Fl E Ar fingerprint_hash
290 Specifies the hash algorithm used when displaying key fingerprints.
298 This option will read a private or public OpenSSH key file and
299 print to stdout a public key in one of the formats specified by the
302 The default export format is
304 This option allows exporting OpenSSH keys for use by other programs, including
305 several commercial SSH implementations.
306 .It Fl F Ar hostname | [hostname]:port
307 Search for the specified
309 (with optional port number)
312 file, listing any occurrences found.
313 This option is useful to find hashed host names or addresses and may also be
314 used in conjunction with the
316 option to print found keys in a hashed format.
318 Specifies the filename of the key file.
319 .It Fl G Ar output_file
320 Generate candidate primes for DH-GEX.
321 These primes must be screened for
326 Use generic DNS format when printing fingerprint resource records using the
333 This replaces all hostnames and addresses with hashed representations
334 within the specified file; the original content is moved to a file with
336 These hashes may be used normally by
340 but they do not reveal identifying information should the file's contents
342 This option will not modify existing hashed hostnames and is therefore safe
343 to use on files that mix hashed and non-hashed names.
345 When signing a key, create a host certificate instead of a user
350 .It Fl I Ar certificate_identity
351 Specify the key identity when signing a public key.
356 This option will read an unencrypted private (or public) key file
357 in the format specified by the
359 option and print an OpenSSH compatible private
360 (or public) key to stdout.
361 This option allows importing keys from other software, including several
362 commercial SSH implementations.
363 The default import format is
365 .It Fl J Ar num_lines
366 Exit after screening the specified number of lines
367 while performing DH candidate screening using the
370 .It Fl j Ar start_line
371 Start screening at the specified line number
372 while performing DH candidate screening using the
376 Write the last line processed to the file
378 while performing DH candidate screening using the
381 This will be used to skip lines in the input file that have already been
382 processed if the job is restarted.
387 will generate a KRL file at the location specified via the
389 flag that revokes every key or certificate presented on the command line.
390 Keys/certificates to be revoked may be specified by public key file or
391 using the format described in the
392 .Sx KEY REVOCATION LISTS
395 Prints the contents of one or more certificates.
397 Show fingerprint of specified public key file.
400 tries to find the matching public key file and prints its fingerprint.
403 a visual ASCII art representation of the key is supplied with the
406 Specify the amount of memory to use (in megabytes) when generating
407 candidate moduli for DH-GEX.
408 .It Fl m Ar key_format
409 Specify a key format for key generation, the
413 (export) conversion options, and the
415 change passphrase operation.
416 The latter may be used to convert between OpenSSH private key and PEM
418 The supported key formats are:
420 (RFC 4716/SSH2 public or private key),
422 (PEM PKCS8 public key)
426 The default conversion format is
430 when generating or updating a supported private key type will cause the
431 key to be stored in the legacy PEM private key format.
432 .It Fl N Ar new_passphrase
433 Provides the new passphrase.
434 .It Fl n Ar principals
435 Specify one or more principals (user or host names) to be included in
436 a certificate when signing a key.
437 Multiple principals may be specified, separated by commas.
442 Specify a certificate option when signing a key.
443 This option may be specified multiple times.
446 section for further details.
448 At present, no standard options are valid for host keys.
449 The options that are valid for user certificates are:
451 .Bl -tag -width Ds -compact
453 Clear all enabled permissions.
454 This is useful for clearing the default set of permissions so permissions may
455 be added individually.
457 .It Ic critical : Ns Ar name Ns Op Ns = Ns Ar contents
458 .It Ic extension : Ns Ar name Ns Op Ns = Ns Ar contents
459 Includes an arbitrary certificate critical option or extension.
462 should include a domain suffix, e.g.\&
463 .Dq name@example.com .
466 is specified then it is included as the contents of the extension/option
467 encoded as a string, otherwise the extension/option is created with no
468 contents (usually indicating a flag).
469 Extensions may be ignored by a client or server that does not recognise them,
470 whereas unknown critical options will cause the certificate to be refused.
472 .It Ic force-command Ns = Ns Ar command
473 Forces the execution of
475 instead of any shell or command specified by the user when
476 the certificate is used for authentication.
478 .It Ic no-agent-forwarding
481 forwarding (permitted by default).
483 .It Ic no-port-forwarding
484 Disable port forwarding (permitted by default).
487 Disable PTY allocation (permitted by default).
494 (permitted by default).
496 .It Ic no-x11-forwarding
497 Disable X11 forwarding (permitted by default).
499 .It Ic permit-agent-forwarding
504 .It Ic permit-port-forwarding
505 Allows port forwarding.
508 Allows PTY allocation.
510 .It Ic permit-user-rc
516 .It Ic permit-X11-forwarding
517 Allows X11 forwarding.
519 .It Ic source-address Ns = Ns Ar address_list
520 Restrict the source addresses from which the certificate is considered valid.
523 is a comma-separated list of one or more address/netmask pairs in CIDR
526 .It Fl P Ar passphrase
527 Provides the (old) passphrase.
529 Requests changing the passphrase of a private key file instead of
530 creating a new private key.
531 The program will prompt for the file
532 containing the private key, for the old passphrase, and twice for the
535 Test whether keys have been revoked in a KRL.
539 .It Fl R Ar hostname | [hostname]:port
540 Removes all keys belonging to the specified
542 (with optional port number)
546 This option is useful to delete hashed hosts (see the
550 Print the SSHFP fingerprint resource record named
552 for the specified public key file.
554 Specify start point (in hex) when generating candidate moduli for DH-GEX.
556 Certify (sign) a public key using the specified CA key.
561 When generating a KRL,
563 specifies a path to a CA public key file used to revoke certificates directly
564 by key ID or serial number.
566 .Sx KEY REVOCATION LISTS
568 .It Fl T Ar output_file
569 Test DH group exchange candidate primes (generated using the
572 .It Fl t Cm dsa | ecdsa | ed25519 | rsa
573 Specifies the type of key to create.
574 The possible values are
581 When used in combination with
583 this option indicates that a CA key resides in a
587 section for more information.
592 keys listed via the command line are added to the existing KRL rather than
593 a new KRL being created.
594 .It Fl V Ar validity_interval
595 Specify a validity interval when signing a certificate.
596 A validity interval may consist of a single time, indicating that the
597 certificate is valid beginning now and expiring at that time, or may consist
598 of two times separated by a colon to indicate an explicit time interval.
600 The start time may be specified as the string
602 to indicate the certificate has no specified start time,
603 a date in YYYYMMDD format, a time in YYYYMMDDHHMM[SS] format,
604 a relative time (to the current time) consisting of a minus sign followed by
605 an interval in the format described in the
606 TIME FORMATS section of
609 The end time may be specified as a YYYYMMDD date, a YYYYMMDDHHMM[SS] time,
610 a relative time starting with a plus character or the string
612 to indicate that the certificate has no expirty date.
616 (valid from now to 52 weeks and one day from now),
618 (valid from four weeks ago to four weeks from now),
619 .Dq 20100101123000:20110101123000
620 (valid from 12:30 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
622 (valid from yesterday to midnight, January 1st, 2011).
624 (valid from one minute ago and never expiring).
629 to print debugging messages about its progress.
630 This is helpful for debugging moduli generation.
633 options increase the verbosity.
635 .It Fl W Ar generator
636 Specify desired generator when testing candidate moduli for DH-GEX.
638 This option will read a private
639 OpenSSH format file and print an OpenSSH public key to stdout.
640 .It Fl z Ar serial_number
641 Specifies a serial number to be embedded in the certificate to distinguish
642 this certificate from others from the same CA.
647 character, then the serial number will be incremented for each certificate
648 signed on a single command-line.
649 The default serial number is zero.
651 When generating a KRL, the
653 flag is used to specify a KRL version number.
655 .Sh MODULI GENERATION
657 may be used to generate groups for the Diffie-Hellman Group Exchange
659 Generating these groups is a two-step process: first, candidate
660 primes are generated using a fast, but memory intensive process.
661 These candidate primes are then tested for suitability (a CPU-intensive
664 Generation of primes is performed using the
667 The desired length of the primes may be specified by the
672 .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
674 By default, the search for primes begins at a random point in the
675 desired length range.
676 This may be overridden using the
678 option, which specifies a different start point (in hex).
680 Once a set of candidates have been generated, they must be screened for
682 This may be performed using the
687 will read candidates from standard input (or a file specified using the
692 .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
694 By default, each candidate will be subjected to 100 primality tests.
695 This may be overridden using the
698 The DH generator value will be chosen automatically for the
699 prime under consideration.
700 If a specific generator is desired, it may be requested using the
703 Valid generator values are 2, 3, and 5.
705 Screened DH groups may be installed in
707 It is important that this file contains moduli of a range of bit lengths and
708 that both ends of a connection share common moduli.
711 supports signing of keys to produce certificates that may be used for
712 user or host authentication.
713 Certificates consist of a public key, some identity information, zero or
714 more principal (user or host) names and a set of options that
715 are signed by a Certification Authority (CA) key.
716 Clients or servers may then trust only the CA key and verify its signature
717 on a certificate rather than trusting many user/host keys.
718 Note that OpenSSH certificates are a different, and much simpler, format to
719 the X.509 certificates used in
723 supports two types of certificates: user and host.
724 User certificates authenticate users to servers, whereas host certificates
725 authenticate server hosts to users.
726 To generate a user certificate:
728 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
730 The resultant certificate will be placed in
731 .Pa /path/to/user_key-cert.pub .
732 A host certificate requires the
736 .Dl $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
738 The host certificate will be output to
739 .Pa /path/to/host_key-cert.pub .
741 It is possible to sign using a CA key stored in a PKCS#11 token by
742 providing the token library using
744 and identifying the CA key by providing its public half as an argument
748 .Dl $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub
750 Similarly, it is possible for the CA key to be hosted in a
752 This is indicated by the
754 flag and, again, the CA key must be identified by its public half.
756 .Dl $ ssh-keygen -Us ca_key.pub -I key_id user_key.pub
760 is a "key identifier" that is logged by the server when the certificate
761 is used for authentication.
763 Certificates may be limited to be valid for a set of principal (user/host)
765 By default, generated certificates are valid for all users or hosts.
766 To generate a certificate for a specified set of principals:
768 .Dl $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
769 .Dl "$ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub"
771 Additional limitations on the validity and use of user certificates may
772 be specified through certificate options.
773 A certificate option may disable features of the SSH session, may be
774 valid only when presented from particular source addresses or may
775 force the use of a specific command.
776 For a list of valid certificate options, see the documentation for the
780 Finally, certificates may be defined with a validity lifetime.
783 option allows specification of certificate start and end times.
784 A certificate that is presented at a time outside this range will not be
786 By default, certificates are valid from
788 Epoch to the distant future.
790 For certificates to be used for user or host authentication, the CA
791 public key must be trusted by
795 Please refer to those manual pages for details.
796 .Sh KEY REVOCATION LISTS
798 is able to manage OpenSSH format Key Revocation Lists (KRLs).
799 These binary files specify keys or certificates to be revoked using a
800 compact format, taking as little as one bit per certificate if they are being
801 revoked by serial number.
803 KRLs may be generated using the
806 This option reads one or more files from the command line and generates a new
808 The files may either contain a KRL specification (see below) or public keys,
810 Plain public keys are revoked by listing their hash or contents in the KRL and
811 certificates revoked by serial number or key ID (if the serial is zero or
814 Revoking keys using a KRL specification offers explicit control over the
815 types of record used to revoke keys and may be used to directly revoke
816 certificates by serial number or key ID without having the complete original
818 A KRL specification consists of lines containing one of the following directives
819 followed by a colon and some directive-specific information.
821 .It Cm serial : Ar serial_number Ns Op - Ns Ar serial_number
822 Revokes a certificate with the specified serial number.
823 Serial numbers are 64-bit values, not including zero and may be expressed
824 in decimal, hex or octal.
825 If two serial numbers are specified separated by a hyphen, then the range
826 of serial numbers including and between each is revoked.
827 The CA key must have been specified on the
829 command line using the
832 .It Cm id : Ar key_id
833 Revokes a certificate with the specified key ID string.
834 The CA key must have been specified on the
836 command line using the
839 .It Cm key : Ar public_key
840 Revokes the specified key.
841 If a certificate is listed, then it is revoked as a plain public key.
842 .It Cm sha1 : Ar public_key
843 Revokes the specified key by including its SHA1 hash in the KRL.
844 .It Cm sha256 : Ar public_key
845 Revokes the specified key by including its SHA256 hash in the KRL.
846 KRLs that revoke keys by SHA256 hash are not supported by OpenSSH versions
848 .It Cm hash : Ar fingerprint
849 Revokes a key using a fingerprint hash, as obtained from a
851 authentication log message or the
855 Only SHA256 fingerprints are supported here and resultant KRLs are
856 not supported by OpenSSH versions prior to 7.9.
859 KRLs may be updated using the
863 When this option is specified, keys listed via the command line are merged into
864 the KRL, adding to those already there.
866 It is also possible, given a KRL, to test whether it revokes a particular key
870 flag will query an existing KRL, testing each key specified on the command line.
871 If any key listed on the command line has been revoked (or an error encountered)
874 will exit with a non-zero exit status.
875 A zero exit status will only be returned if no key was revoked.
877 .Bl -tag -width Ds -compact
879 .It Pa ~/.ssh/id_ecdsa
880 .It Pa ~/.ssh/id_ed25519
882 Contains the DSA, ECDSA, Ed25519 or RSA
883 authentication identity of the user.
884 This file should not be readable by anyone but the user.
886 specify a passphrase when generating the key; that passphrase will be
887 used to encrypt the private part of this file using 128-bit AES.
888 This file is not automatically accessed by
890 but it is offered as the default file for the private key.
892 will read this file when a login attempt is made.
894 .It Pa ~/.ssh/id_dsa.pub
895 .It Pa ~/.ssh/id_ecdsa.pub
896 .It Pa ~/.ssh/id_ed25519.pub
897 .It Pa ~/.ssh/id_rsa.pub
898 Contains the DSA, ECDSA, Ed25519 or RSA
899 public key for authentication.
900 The contents of this file should be added to
901 .Pa ~/.ssh/authorized_keys
903 where the user wishes to log in using public key authentication.
904 There is no need to keep the contents of this file secret.
907 Contains Diffie-Hellman groups used for DH-GEX.
908 The file format is described in
919 .%T "The Secure Shell (SSH) Public Key File Format"
923 OpenSSH is a derivative of the original and free
924 ssh 1.2.12 release by Tatu Ylonen.
925 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
926 Theo de Raadt and Dug Song
927 removed many bugs, re-added newer features and
929 Markus Friedl contributed the support for SSH
930 protocol versions 1.5 and 2.0.
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