1SSH-KEYGEN(1) OpenBSD Reference Manual SSH-KEYGEN(1) 2 3NAME 4 ssh-keygen - authentication key generation, management and conversion 5 6SYNOPSIS 7 ssh-keygen [-q] [-b bits] [-t type] [-N new_passphrase] [-C comment] 8 [-f output_keyfile] 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] 16 ssh-keygen -D pkcs11 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 rounds] [-J num_lines] 23 [-j start_line] [-K checkpt] [-W generator] 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] 27 ssh-keygen -A 28 ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number] 29 file ... 30 ssh-keygen -Q -f krl_file file ... 31 32DESCRIPTION 33 ssh-keygen generates, manages and converts authentication keys for 34 ssh(1). ssh-keygen can create RSA keys for use by SSH protocol version 1 35 and DSA, ECDSA, ED25519 or RSA keys for use by SSH protocol version 2. 36 The type of key to be generated is specified with the -t option. If 37 invoked without any arguments, ssh-keygen will generate an RSA key for 38 use in SSH protocol 2 connections. 39 40 ssh-keygen is also used to generate groups for use in Diffie-Hellman 41 group exchange (DH-GEX). See the MODULI GENERATION section for details. 42 43 Finally, ssh-keygen can be used to generate and update Key Revocation 44 Lists, and to test whether given keys have been revoked by one. See the 45 KEY REVOCATION LISTS section for details. 46 47 Normally each user wishing to use SSH with public key authentication runs 48 this once to create the authentication key in ~/.ssh/identity, 49 ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 or ~/.ssh/id_rsa. 50 Additionally, the system administrator may use this to generate host 51 keys, as seen in /etc/rc. 52 53 Normally this program generates the key and asks for a file in which to 54 store the private key. The public key is stored in a file with the same 55 name but ``.pub'' appended. The program also asks for a passphrase. The 56 passphrase may be empty to indicate no passphrase (host keys must have an 57 empty passphrase), or it may be a string of arbitrary length. A 58 passphrase is similar to a password, except it can be a phrase with a 59 series of words, punctuation, numbers, whitespace, or any string of 60 characters you want. Good passphrases are 10-30 characters long, are not 61 simple sentences or otherwise easily guessable (English prose has only 62 1-2 bits of entropy per character, and provides very bad passphrases), 63 and contain a mix of upper and lowercase letters, numbers, and non- 64 alphanumeric characters. The passphrase can be changed later by using 65 the -p option. 66 67 There is no way to recover a lost passphrase. If the passphrase is lost 68 or forgotten, a new key must be generated and the corresponding public 69 key copied to other machines. 70 71 For RSA1 keys, there is also a comment field in the key file that is only 72 for convenience to the user to help identify the key. The comment can 73 tell what the key is for, or whatever is useful. The comment is 74 initialized to ``user@host'' when the key is created, but can be changed 75 using the -c option. 76 77 After a key is generated, instructions below detail where the keys should 78 be placed to be activated. 79 80 The options are as follows: 81 82 -A For each of the key types (rsa1, rsa, dsa, ecdsa and ed25519) for 83 which host keys do not exist, generate the host keys with the 84 default key file path, an empty passphrase, default bits for the 85 key type, and default comment. This is used by /etc/rc to 86 generate new host keys. 87 88 -a rounds 89 When saving a new-format private key (i.e. an ed25519 key or any 90 SSH protocol 2 key when the -o flag is set), this option 91 specifies the number of KDF (key derivation function) rounds 92 used. Higher numbers result in slower passphrase verification 93 and increased resistance to brute-force password cracking (should 94 the keys be stolen). 95 96 When screening DH-GEX candidates ( using the -T command). This 97 option specifies the number of primality tests to perform. 98 99 -B Show the bubblebabble digest of specified private or public key 100 file. 101 102 -b bits 103 Specifies the number of bits in the key to create. For RSA keys, 104 the minimum size is 768 bits and the default is 2048 bits. 105 Generally, 2048 bits is considered sufficient. DSA keys must be 106 exactly 1024 bits as specified by FIPS 186-2. For ECDSA keys, 107 the -b flag determines the key length by selecting from one of 108 three elliptic curve sizes: 256, 384 or 521 bits. Attempting to 109 use bit lengths other than these three values for ECDSA keys will 110 fail. ED25519 keys have a fixed length and the -b flag will be 111 ignored. 112 113 -C comment 114 Provides a new comment. 115 116 -c Requests changing the comment in the private and public key 117 files. This operation is only supported for RSA1 keys. The 118 program will prompt for the file containing the private keys, for 119 the passphrase if the key has one, and for the new comment. 120 121 -D pkcs11 122 Download the RSA public keys provided by the PKCS#11 shared 123 library pkcs11. When used in combination with -s, this option 124 indicates that a CA key resides in a PKCS#11 token (see the 125 CERTIFICATES section for details). 126 127 -e This option will read a private or public OpenSSH key file and 128 print to stdout the key in one of the formats specified by the -m 129 option. The default export format is ``RFC4716''. This option 130 allows exporting OpenSSH keys for use by other programs, 131 including several commercial SSH implementations. 132 133 -F hostname 134 Search for the specified hostname in a known_hosts file, listing 135 any occurrences found. This option is useful to find hashed host 136 names or addresses and may also be used in conjunction with the 137 -H option to print found keys in a hashed format. 138 139 -f filename 140 Specifies the filename of the key file. 141 142 -G output_file 143 Generate candidate primes for DH-GEX. These primes must be 144 screened for safety (using the -T option) before use. 145 146 -g Use generic DNS format when printing fingerprint resource records 147 using the -r command. 148 149 -H Hash a known_hosts file. This replaces all hostnames and 150 addresses with hashed representations within the specified file; 151 the original content is moved to a file with a .old suffix. 152 These hashes may be used normally by ssh and sshd, but they do 153 not reveal identifying information should the file's contents be 154 disclosed. This option will not modify existing hashed hostnames 155 and is therefore safe to use on files that mix hashed and non- 156 hashed names. 157 158 -h When signing a key, create a host certificate instead of a user 159 certificate. Please see the CERTIFICATES section for details. 160 161 -I certificate_identity 162 Specify the key identity when signing a public key. Please see 163 the CERTIFICATES section for details. 164 165 -i This option will read an unencrypted private (or public) key file 166 in the format specified by the -m option and print an OpenSSH 167 compatible private (or public) key to stdout. 168 169 -J num_lines 170 Exit after screening the specified number of lines while 171 performing DH candidate screening using the -T option. 172 173 -j start_line 174 Start screening at the specified line number while performing DH 175 candidate screening using the -T option. 176 177 -K checkpt 178 Write the last line processed to the file checkpt while 179 performing DH candidate screening using the -T option. This will 180 be used to skip lines in the input file that have already been 181 processed if the job is restarted. This option allows importing 182 keys from other software, including several commercial SSH 183 implementations. The default import format is ``RFC4716''. 184 185 -k Generate a KRL file. In this mode, ssh-keygen will generate a 186 KRL file at the location specified via the -f flag that revokes 187 every key or certificate presented on the command line. 188 Keys/certificates to be revoked may be specified by public key 189 file or using the format described in the KEY REVOCATION LISTS 190 section. 191 192 -L Prints the contents of a certificate. 193 194 -l Show fingerprint of specified public key file. Private RSA1 keys 195 are also supported. For RSA and DSA keys ssh-keygen tries to 196 find the matching public key file and prints its fingerprint. If 197 combined with -v, an ASCII art representation of the key is 198 supplied with the fingerprint. 199 200 -M memory 201 Specify the amount of memory to use (in megabytes) when 202 generating candidate moduli for DH-GEX. 203 204 -m key_format 205 Specify a key format for the -i (import) or -e (export) 206 conversion options. The supported key formats are: ``RFC4716'' 207 (RFC 4716/SSH2 public or private key), ``PKCS8'' (PEM PKCS8 208 public key) or ``PEM'' (PEM public key). The default conversion 209 format is ``RFC4716''. 210 211 -N new_passphrase 212 Provides the new passphrase. 213 214 -n principals 215 Specify one or more principals (user or host names) to be 216 included in a certificate when signing a key. Multiple 217 principals may be specified, separated by commas. Please see the 218 CERTIFICATES section for details. 219 220 -O option 221 Specify a certificate option when signing a key. This option may 222 be specified multiple times. Please see the CERTIFICATES section 223 for details. The options that are valid for user certificates 224 are: 225 226 clear Clear all enabled permissions. This is useful for 227 clearing the default set of permissions so permissions 228 may be added individually. 229 230 force-command=command 231 Forces the execution of command instead of any shell or 232 command specified by the user when the certificate is 233 used for authentication. 234 235 no-agent-forwarding 236 Disable ssh-agent(1) forwarding (permitted by default). 237 238 no-port-forwarding 239 Disable port forwarding (permitted by default). 240 241 no-pty Disable PTY allocation (permitted by default). 242 243 no-user-rc 244 Disable execution of ~/.ssh/rc by sshd(8) (permitted by 245 default). 246 247 no-x11-forwarding 248 Disable X11 forwarding (permitted by default). 249 250 permit-agent-forwarding 251 Allows ssh-agent(1) forwarding. 252 253 permit-port-forwarding 254 Allows port forwarding. 255 256 permit-pty 257 Allows PTY allocation. 258 259 permit-user-rc 260 Allows execution of ~/.ssh/rc by sshd(8). 261 262 permit-x11-forwarding 263 Allows X11 forwarding. 264 265 source-address=address_list 266 Restrict the source addresses from which the certificate 267 is considered valid. The address_list is a comma- 268 separated list of one or more address/netmask pairs in 269 CIDR format. 270 271 At present, no options are valid for host keys. 272 273 -o Causes ssh-keygen to save SSH protocol 2 private keys using the 274 new OpenSSH format rather than the more compatible PEM format. 275 The new format has increased resistance to brute-force password 276 cracking but is not supported by versions of OpenSSH prior to 277 6.5. Ed25519 keys always use the new private key format. 278 279 -P passphrase 280 Provides the (old) passphrase. 281 282 -p Requests changing the passphrase of a private key file instead of 283 creating a new private key. The program will prompt for the file 284 containing the private key, for the old passphrase, and twice for 285 the new passphrase. 286 287 -Q Test whether keys have been revoked in a KRL. 288 289 -q Silence ssh-keygen. 290 291 -R hostname 292 Removes all keys belonging to hostname from a known_hosts file. 293 This option is useful to delete hashed hosts (see the -H option 294 above). 295 296 -r hostname 297 Print the SSHFP fingerprint resource record named hostname for 298 the specified public key file. 299 300 -S start 301 Specify start point (in hex) when generating candidate moduli for 302 DH-GEX. 303 304 -s ca_key 305 Certify (sign) a public key using the specified CA key. Please 306 see the CERTIFICATES section for details. 307 308 When generating a KRL, -s specifies a path to a CA public key 309 file used to revoke certificates directly by key ID or serial 310 number. See the KEY REVOCATION LISTS section for details. 311 312 -T output_file 313 Test DH group exchange candidate primes (generated using the -G 314 option) for safety. 315 316 -t type 317 Specifies the type of key to create. The possible values are 318 ``rsa1'' for protocol version 1 and ``dsa'', ``ecdsa'', 319 ``ed25519'', or ``rsa'' for protocol version 2. 320 321 -u Update a KRL. When specified with -k, keys listed via the 322 command line are added to the existing KRL rather than a new KRL 323 being created. 324 325 -V validity_interval 326 Specify a validity interval when signing a certificate. A 327 validity interval may consist of a single time, indicating that 328 the certificate is valid beginning now and expiring at that time, 329 or may consist of two times separated by a colon to indicate an 330 explicit time interval. The start time may be specified as a 331 date in YYYYMMDD format, a time in YYYYMMDDHHMMSS format or a 332 relative time (to the current time) consisting of a minus sign 333 followed by a relative time in the format described in the TIME 334 FORMATS section of sshd_config(5). The end time may be specified 335 as a YYYYMMDD date, a YYYYMMDDHHMMSS time or a relative time 336 starting with a plus character. 337 338 For example: ``+52w1d'' (valid from now to 52 weeks and one day 339 from now), ``-4w:+4w'' (valid from four weeks ago to four weeks 340 from now), ``20100101123000:20110101123000'' (valid from 12:30 341 PM, January 1st, 2010 to 12:30 PM, January 1st, 2011), 342 ``-1d:20110101'' (valid from yesterday to midnight, January 1st, 343 2011). 344 345 -v Verbose mode. Causes ssh-keygen to print debugging messages 346 about its progress. This is helpful for debugging moduli 347 generation. Multiple -v options increase the verbosity. The 348 maximum is 3. 349 350 -W generator 351 Specify desired generator when testing candidate moduli for DH- 352 GEX. 353 354 -y This option will read a private OpenSSH format file and print an 355 OpenSSH public key to stdout. 356 357 -z serial_number 358 Specifies a serial number to be embedded in the certificate to 359 distinguish this certificate from others from the same CA. The 360 default serial number is zero. 361 362 When generating a KRL, the -z flag is used to specify a KRL 363 version number. 364 365MODULI GENERATION 366 ssh-keygen may be used to generate groups for the Diffie-Hellman Group 367 Exchange (DH-GEX) protocol. Generating these groups is a two-step 368 process: first, candidate primes are generated using a fast, but memory 369 intensive process. These candidate primes are then tested for 370 suitability (a CPU-intensive process). 371 372 Generation of primes is performed using the -G option. The desired 373 length of the primes may be specified by the -b option. For example: 374 375 # ssh-keygen -G moduli-2048.candidates -b 2048 376 377 By default, the search for primes begins at a random point in the desired 378 length range. This may be overridden using the -S option, which 379 specifies a different start point (in hex). 380 381 Once a set of candidates have been generated, they must be screened for 382 suitability. This may be performed using the -T option. In this mode 383 ssh-keygen will read candidates from standard input (or a file specified 384 using the -f option). For example: 385 386 # ssh-keygen -T moduli-2048 -f moduli-2048.candidates 387 388 By default, each candidate will be subjected to 100 primality tests. 389 This may be overridden using the -a option. The DH generator value will 390 be chosen automatically for the prime under consideration. If a specific 391 generator is desired, it may be requested using the -W option. Valid 392 generator values are 2, 3, and 5. 393 394 Screened DH groups may be installed in /etc/moduli. It is important that 395 this file contains moduli of a range of bit lengths and that both ends of 396 a connection share common moduli. 397 398CERTIFICATES 399 ssh-keygen supports signing of keys to produce certificates that may be 400 used for user or host authentication. Certificates consist of a public 401 key, some identity information, zero or more principal (user or host) 402 names and a set of options that are signed by a Certification Authority 403 (CA) key. Clients or servers may then trust only the CA key and verify 404 its signature on a certificate rather than trusting many user/host keys. 405 Note that OpenSSH certificates are a different, and much simpler, format 406 to the X.509 certificates used in ssl(8). 407 408 ssh-keygen supports two types of certificates: user and host. User 409 certificates authenticate users to servers, whereas host certificates 410 authenticate server hosts to users. To generate a user certificate: 411 412 $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub 413 414 The resultant certificate will be placed in /path/to/user_key-cert.pub. 415 A host certificate requires the -h option: 416 417 $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub 418 419 The host certificate will be output to /path/to/host_key-cert.pub. 420 421 It is possible to sign using a CA key stored in a PKCS#11 token by 422 providing the token library using -D and identifying the CA key by 423 providing its public half as an argument to -s: 424 425 $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id host_key.pub 426 427 In all cases, key_id is a "key identifier" that is logged by the server 428 when the certificate is used for authentication. 429 430 Certificates may be limited to be valid for a set of principal 431 (user/host) names. By default, generated certificates are valid for all 432 users or hosts. To generate a certificate for a specified set of 433 principals: 434 435 $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub 436 $ ssh-keygen -s ca_key -I key_id -h -n host.domain user_key.pub 437 438 Additional limitations on the validity and use of user certificates may 439 be specified through certificate options. A certificate option may 440 disable features of the SSH session, may be valid only when presented 441 from particular source addresses or may force the use of a specific 442 command. For a list of valid certificate options, see the documentation 443 for the -O option above. 444 445 Finally, certificates may be defined with a validity lifetime. The -V 446 option allows specification of certificate start and end times. A 447 certificate that is presented at a time outside this range will not be 448 considered valid. By default, certificates are valid from UNIX Epoch to 449 the distant future. 450 451 For certificates to be used for user or host authentication, the CA 452 public key must be trusted by sshd(8) or ssh(1). Please refer to those 453 manual pages for details. 454 455KEY REVOCATION LISTS 456 ssh-keygen is able to manage OpenSSH format Key Revocation Lists (KRLs). 457 These binary files specify keys or certificates to be revoked using a 458 compact format, taking as little as one bit per certificate if they are 459 being revoked by serial number. 460 461 KRLs may be generated using the -k flag. This option reads one or more 462 files from the command line and generates a new KRL. The files may 463 either contain a KRL specification (see below) or public keys, listed one 464 per line. Plain public keys are revoked by listing their hash or 465 contents in the KRL and certificates revoked by serial number or key ID 466 (if the serial is zero or not available). 467 468 Revoking keys using a KRL specification offers explicit control over the 469 types of record used to revoke keys and may be used to directly revoke 470 certificates by serial number or key ID without having the complete 471 original certificate on hand. A KRL specification consists of lines 472 containing one of the following directives followed by a colon and some 473 directive-specific information. 474 475 serial: serial_number[-serial_number] 476 Revokes a certificate with the specified serial number. Serial 477 numbers are 64-bit values, not including zero and may be 478 expressed in decimal, hex or octal. If two serial numbers are 479 specified separated by a hyphen, then the range of serial numbers 480 including and between each is revoked. The CA key must have been 481 specified on the ssh-keygen command line using the -s option. 482 483 id: key_id 484 Revokes a certificate with the specified key ID string. The CA 485 key must have been specified on the ssh-keygen command line using 486 the -s option. 487 488 key: public_key 489 Revokes the specified key. If a certificate is listed, then it 490 is revoked as a plain public key. 491 492 sha1: public_key 493 Revokes the specified key by its SHA1 hash. 494 495 KRLs may be updated using the -u flag in addition to -k. When this 496 option is specified, keys listed via the command line are merged into the 497 KRL, adding to those already there. 498 499 It is also possible, given a KRL, to test whether it revokes a particular 500 key (or keys). The -Q flag will query an existing KRL, testing each key 501 specified on the commandline. If any key listed on the command line has 502 been revoked (or an error encountered) then ssh-keygen will exit with a 503 non-zero exit status. A zero exit status will only be returned if no key 504 was revoked. 505 506FILES 507 ~/.ssh/identity 508 Contains the protocol version 1 RSA authentication identity of 509 the user. This file should not be readable by anyone but the 510 user. It is possible to specify a passphrase when generating the 511 key; that passphrase will be used to encrypt the private part of 512 this file using 3DES. This file is not automatically accessed by 513 ssh-keygen but it is offered as the default file for the private 514 key. ssh(1) will read this file when a login attempt is made. 515 516 ~/.ssh/identity.pub 517 Contains the protocol version 1 RSA public key for 518 authentication. The contents of this file should be added to 519 ~/.ssh/authorized_keys on all machines where the user wishes to 520 log in using RSA authentication. There is no need to keep the 521 contents of this file secret. 522 523 ~/.ssh/id_dsa 524 ~/.ssh/id_ecdsa 525 ~/.ssh/id_ed25519 526 ~/.ssh/id_rsa 527 Contains the protocol version 2 DSA, ECDSA, ED25519 or RSA 528 authentication identity of the user. This file should not be 529 readable by anyone but the user. It is possible to specify a 530 passphrase when generating the key; that passphrase will be used 531 to encrypt the private part of this file using 128-bit AES. This 532 file is not automatically accessed by ssh-keygen but it is 533 offered as the default file for the private key. ssh(1) will 534 read this file when a login attempt is made. 535 536 ~/.ssh/id_dsa.pub 537 ~/.ssh/id_ecdsa.pub 538 ~/.ssh/id_ed25519.pub 539 ~/.ssh/id_rsa.pub 540 Contains the protocol version 2 DSA, ECDSA, ED25519 or RSA public 541 key for authentication. The contents of this file should be 542 added to ~/.ssh/authorized_keys on all machines where the user 543 wishes to log in using public key authentication. There is no 544 need to keep the contents of this file secret. 545 546 /etc/moduli 547 Contains Diffie-Hellman groups used for DH-GEX. The file format 548 is described in moduli(5). 549 550SEE ALSO 551 ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8) 552 553 The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006. 554 555AUTHORS 556 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 557 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 558 de Raadt and Dug Song removed many bugs, re-added newer features and 559 created OpenSSH. Markus Friedl contributed the support for SSH protocol 560 versions 1.5 and 2.0. 561 562OpenBSD 5.5 February 5, 2014 OpenBSD 5.5 563