1 SSH-KEYGEN(1) OpenBSD Reference Manual SSH-KEYGEN(1)
4 ssh-keygen - authentication key generation, management and conversion
7 ssh-keygen [-q] [-b bits] -t type [-N new_passphrase] [-C comment]
9 ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile]
10 ssh-keygen -i [-m key_format] [-f input_keyfile]
11 ssh-keygen -e [-m key_format] [-f input_keyfile]
12 ssh-keygen -y [-f input_keyfile]
13 ssh-keygen -c [-P passphrase] [-C comment] [-f keyfile]
14 ssh-keygen -l [-f input_keyfile]
15 ssh-keygen -B [-f input_keyfile]
17 ssh-keygen -F hostname [-f known_hosts_file] [-l]
18 ssh-keygen -H [-f known_hosts_file]
19 ssh-keygen -R hostname [-f known_hosts_file]
20 ssh-keygen -r hostname [-f input_keyfile] [-g]
21 ssh-keygen -G output_file [-v] [-b bits] [-M memory] [-S start_point]
22 ssh-keygen -T output_file -f input_file [-v] [-a num_trials]
24 ssh-keygen -s ca_key -I certificate_identity [-h] [-n principals]
25 [-O option] [-V validity_interval] [-z serial_number] file ...
26 ssh-keygen -L [-f input_keyfile]
29 ssh-keygen generates, manages and converts authentication keys for
30 ssh(1). ssh-keygen can create RSA keys for use by SSH protocol version 1
31 and DSA, ECDSA or RSA keys for use by SSH protocol version 2. The type
32 of key to be generated is specified with the -t option. If invoked
33 without any arguments, ssh-keygen will generate an RSA key for use in SSH
34 protocol 2 connections.
36 ssh-keygen is also used to generate groups for use in Diffie-Hellman
37 group exchange (DH-GEX). See the MODULI GENERATION section for details.
39 Normally each user wishing to use SSH with public key authentication runs
40 this once to create the authentication key in ~/.ssh/identity,
41 ~/.ssh/id_ecdsa, ~/.ssh/id_dsa or ~/.ssh/id_rsa. Additionally, the
42 system administrator may use this to generate host keys, as seen in
45 Normally this program generates the key and asks for a file in which to
46 store the private key. The public key is stored in a file with the same
47 name but ``.pub'' appended. The program also asks for a passphrase. The
48 passphrase may be empty to indicate no passphrase (host keys must have an
49 empty passphrase), or it may be a string of arbitrary length. A
50 passphrase is similar to a password, except it can be a phrase with a
51 series of words, punctuation, numbers, whitespace, or any string of
52 characters you want. Good passphrases are 10-30 characters long, are not
53 simple sentences or otherwise easily guessable (English prose has only 1-
54 2 bits of entropy per character, and provides very bad passphrases), and
55 contain a mix of upper and lowercase letters, numbers, and non-
56 alphanumeric characters. The passphrase can be changed later by using
59 There is no way to recover a lost passphrase. If the passphrase is lost
60 or forgotten, a new key must be generated and copied to the corresponding
61 public key to other machines.
63 For RSA1 keys, there is also a comment field in the key file that is only
64 for convenience to the user to help identify the key. The comment can
65 tell what the key is for, or whatever is useful. The comment is
66 initialized to ``user@host'' when the key is created, but can be changed
69 After a key is generated, instructions below detail where the keys should
70 be placed to be activated.
72 The options are as follows:
75 Specifies the number of primality tests to perform when screening
76 DH-GEX candidates using the -T command.
78 -B Show the bubblebabble digest of specified private or public key
82 Specifies the number of bits in the key to create. For RSA keys,
83 the minimum size is 768 bits and the default is 2048 bits.
84 Generally, 2048 bits is considered sufficient. DSA keys must be
85 exactly 1024 bits as specified by FIPS 186-2.
88 Provides a new comment.
90 -c Requests changing the comment in the private and public key
91 files. This operation is only supported for RSA1 keys. The
92 program will prompt for the file containing the private keys, for
93 the passphrase if the key has one, and for the new comment.
96 Download the RSA public keys provided by the PKCS#11 shared
97 library pkcs11. When used in combination with -s, this option
98 indicates that a CA key resides in a PKCS#11 token (see the
99 CERTIFICATES section for details).
101 -e This option will read a private or public OpenSSH key file and
102 print to stdout the key in one of the formats specified by the -m
103 option. The default export format is ``RFC4716''. This option
104 allows exporting OpenSSH keys for use by other programs,
105 including several commercial SSH implementations.
108 Search for the specified hostname in a known_hosts file, listing
109 any occurrences found. This option is useful to find hashed host
110 names or addresses and may also be used in conjunction with the
111 -H option to print found keys in a hashed format.
114 Specifies the filename of the key file.
117 Generate candidate primes for DH-GEX. These primes must be
118 screened for safety (using the -T option) before use.
120 -g Use generic DNS format when printing fingerprint resource records
121 using the -r command.
123 -H Hash a known_hosts file. This replaces all hostnames and
124 addresses with hashed representations within the specified file;
125 the original content is moved to a file with a .old suffix.
126 These hashes may be used normally by ssh and sshd, but they do
127 not reveal identifying information should the file's contents be
128 disclosed. This option will not modify existing hashed hostnames
129 and is therefore safe to use on files that mix hashed and non-
132 -h When signing a key, create a host certificate instead of a user
133 certificate. Please see the CERTIFICATES section for details.
135 -I certificate_identity
136 Specify the key identity when signing a public key. Please see
137 the CERTIFICATES section for details.
139 -i This option will read an unencrypted private (or public) key file
140 in the format specified by the -m option and print an OpenSSH
141 compatible private (or public) key to stdout. This option allows
142 importing keys from other software, including several commercial
143 SSH implementations. The default import format is ``RFC4716''.
145 -L Prints the contents of a certificate.
147 -l Show fingerprint of specified public key file. Private RSA1 keys
148 are also supported. For RSA and DSA keys ssh-keygen tries to
149 find the matching public key file and prints its fingerprint. If
150 combined with -v, an ASCII art representation of the key is
151 supplied with the fingerprint.
154 Specify the amount of memory to use (in megabytes) when
155 generating candidate moduli for DH-GEX.
158 Specify a key format for the -i (import) or -e (export)
159 conversion options. The supported key formats are: ``RFC4716''
160 (RFC 4716/SSH2 public or private key), ``PKCS8'' (PEM PKCS8
161 public key) or ``PEM'' (PEM public key). The default conversion
162 format is ``RFC4716''.
165 Provides the new passphrase.
168 Specify one or more principals (user or host names) to be
169 included in a certificate when signing a key. Multiple
170 principals may be specified, separated by commas. Please see the
171 CERTIFICATES section for details.
174 Specify a certificate option when signing a key. This option may
175 be specified multiple times. Please see the CERTIFICATES section
176 for details. The options that are valid for user certificates
179 clear Clear all enabled permissions. This is useful for
180 clearing the default set of permissions so permissions
181 may be added individually.
183 force-command=command
184 Forces the execution of command instead of any shell or
185 command specified by the user when the certificate is
186 used for authentication.
189 Disable ssh-agent(1) forwarding (permitted by default).
192 Disable port forwarding (permitted by default).
194 no-pty Disable PTY allocation (permitted by default).
197 Disable execution of ~/.ssh/rc by sshd(8) (permitted by
201 Disable X11 forwarding (permitted by default).
203 permit-agent-forwarding
204 Allows ssh-agent(1) forwarding.
206 permit-port-forwarding
207 Allows port forwarding.
210 Allows PTY allocation.
213 Allows execution of ~/.ssh/rc by sshd(8).
215 permit-x11-forwarding
216 Allows X11 forwarding.
218 source-address=address_list
219 Restrict the source addresses from which the certificate
220 is considered valid. The address_list is a comma-
221 separated list of one or more address/netmask pairs in
224 At present, no options are valid for host keys.
227 Provides the (old) passphrase.
229 -p Requests changing the passphrase of a private key file instead of
230 creating a new private key. The program will prompt for the file
231 containing the private key, for the old passphrase, and twice for
234 -q Silence ssh-keygen. Used by /etc/rc when creating a new key.
237 Removes all keys belonging to hostname from a known_hosts file.
238 This option is useful to delete hashed hosts (see the -H option
242 Print the SSHFP fingerprint resource record named hostname for
243 the specified public key file.
246 Specify start point (in hex) when generating candidate moduli for
250 Certify (sign) a public key using the specified CA key. Please
251 see the CERTIFICATES section for details.
254 Test DH group exchange candidate primes (generated using the -G
258 Specifies the type of key to create. The possible values are
259 ``rsa1'' for protocol version 1 and ``dsa'', ``ecdsa'' or ``rsa''
260 for protocol version 2.
263 Specify a validity interval when signing a certificate. A
264 validity interval may consist of a single time, indicating that
265 the certificate is valid beginning now and expiring at that time,
266 or may consist of two times separated by a colon to indicate an
267 explicit time interval. The start time may be specified as a
268 date in YYYYMMDD format, a time in YYYYMMDDHHMMSS format or a
269 relative time (to the current time) consisting of a minus sign
270 followed by a relative time in the format described in the TIME
271 FORMATS section of sshd_config(5). The end time may be specified
272 as a YYYYMMDD date, a YYYYMMDDHHMMSS time or a relative time
273 starting with a plus character.
275 For example: ``+52w1d'' (valid from now to 52 weeks and one day
276 from now), ``-4w:+4w'' (valid from four weeks ago to four weeks
277 from now), ``20100101123000:20110101123000'' (valid from 12:30
278 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011),
279 ``-1d:20110101'' (valid from yesterday to midnight, January 1st,
282 -v Verbose mode. Causes ssh-keygen to print debugging messages
283 about its progress. This is helpful for debugging moduli
284 generation. Multiple -v options increase the verbosity. The
288 Specify desired generator when testing candidate moduli for DH-
291 -y This option will read a private OpenSSH format file and print an
292 OpenSSH public key to stdout.
295 Specifies a serial number to be embedded in the certificate to
296 distinguish this certificate from others from the same CA. The
297 default serial number is zero.
300 ssh-keygen may be used to generate groups for the Diffie-Hellman Group
301 Exchange (DH-GEX) protocol. Generating these groups is a two-step
302 process: first, candidate primes are generated using a fast, but memory
303 intensive process. These candidate primes are then tested for
304 suitability (a CPU-intensive process).
306 Generation of primes is performed using the -G option. The desired
307 length of the primes may be specified by the -b option. For example:
309 # ssh-keygen -G moduli-2048.candidates -b 2048
311 By default, the search for primes begins at a random point in the desired
312 length range. This may be overridden using the -S option, which
313 specifies a different start point (in hex).
315 Once a set of candidates have been generated, they must be tested for
316 suitability. This may be performed using the -T option. In this mode
317 ssh-keygen will read candidates from standard input (or a file specified
318 using the -f option). For example:
320 # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
322 By default, each candidate will be subjected to 100 primality tests.
323 This may be overridden using the -a option. The DH generator value will
324 be chosen automatically for the prime under consideration. If a specific
325 generator is desired, it may be requested using the -W option. Valid
326 generator values are 2, 3, and 5.
328 Screened DH groups may be installed in /etc/moduli. It is important that
329 this file contains moduli of a range of bit lengths and that both ends of
330 a connection share common moduli.
333 ssh-keygen supports signing of keys to produce certificates that may be
334 used for user or host authentication. Certificates consist of a public
335 key, some identity information, zero or more principal (user or host)
336 names and a set of options that are signed by a Certification Authority
337 (CA) key. Clients or servers may then trust only the CA key and verify
338 its signature on a certificate rather than trusting many user/host keys.
339 Note that OpenSSH certificates are a different, and much simpler, format
340 to the X.509 certificates used in ssl(8).
342 ssh-keygen supports two types of certificates: user and host. User
343 certificates authenticate users to servers, whereas host certificates
344 authenticate server hosts to users. To generate a user certificate:
346 $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub
348 The resultant certificate will be placed in /path/to/user_key-cert.pub.
349 A host certificate requires the -h option:
351 $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub
353 The host certificate will be output to /path/to/host_key-cert.pub.
355 It is possible to sign using a CA key stored in a PKCS#11 token by
356 providing the token library using -D and identifying the CA key by
357 providing its public half as an argument to -s:
359 $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id host_key.pub
361 In all cases, key_id is a "key identifier" that is logged by the server
362 when the certificate is used for authentication.
364 Certificates may be limited to be valid for a set of principal
365 (user/host) names. By default, generated certificates are valid for all
366 users or hosts. To generate a certificate for a specified set of
369 $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub
370 $ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub
372 Additional limitations on the validity and use of user certificates may
373 be specified through certificate options. A certificate option may
374 disable features of the SSH session, may be valid only when presented
375 from particular source addresses or may force the use of a specific
376 command. For a list of valid certificate options, see the documentation
377 for the -O option above.
379 Finally, certificates may be defined with a validity lifetime. The -V
380 option allows specification of certificate start and end times. A
381 certificate that is presented at a time outside this range will not be
382 considered valid. By default, certificates have a maximum validity
385 For certificates to be used for user or host authentication, the CA
386 public key must be trusted by sshd(8) or ssh(1). Please refer to those
387 manual pages for details.
391 Contains the protocol version 1 RSA authentication identity of
392 the user. This file should not be readable by anyone but the
393 user. It is possible to specify a passphrase when generating the
394 key; that passphrase will be used to encrypt the private part of
395 this file using 3DES. This file is not automatically accessed by
396 ssh-keygen but it is offered as the default file for the private
397 key. ssh(1) will read this file when a login attempt is made.
400 Contains the protocol version 1 RSA public key for
401 authentication. The contents of this file should be added to
402 ~/.ssh/authorized_keys on all machines where the user wishes to
403 log in using RSA authentication. There is no need to keep the
404 contents of this file secret.
409 Contains the protocol version 2 DSA, ECDSA or RSA authentication
410 identity of the user. This file should not be readable by anyone
411 but the user. It is possible to specify a passphrase when
412 generating the key; that passphrase will be used to encrypt the
413 private part of this file using 128-bit AES. This file is not
414 automatically accessed by ssh-keygen but it is offered as the
415 default file for the private key. ssh(1) will read this file
416 when a login attempt is made.
421 Contains the protocol version 2 DSA, ECDSA or RSA public key for
422 authentication. The contents of this file should be added to
423 ~/.ssh/authorized_keys on all machines where the user wishes to
424 log in using public key authentication. There is no need to keep
425 the contents of this file secret.
428 Contains Diffie-Hellman groups used for DH-GEX. The file format
429 is described in moduli(5).
432 ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
434 The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006.
437 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
438 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
439 de Raadt and Dug Song removed many bugs, re-added newer features and
440 created OpenSSH. Markus Friedl contributed the support for SSH protocol
441 versions 1.5 and 2.0.
443 OpenBSD 4.9 October 28, 2010 OpenBSD 4.9