1 SSH-KEYGEN(1) General Commands Manual SSH-KEYGEN(1) 2 3 NAME 4 ssh-keygen M-bM-^@M-^S authentication key generation, management and conversion 5 6 SYNOPSIS 7 ssh-keygen [-q] [-b bits] [-t dsa | ecdsa | ed25519 | rsa | rsa1] 8 [-N new_passphrase] [-C comment] [-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 [-v] [-E fingerprint_hash] [-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 32 DESCRIPTION 33 ssh-keygen generates, manages and converts authentication keys for 34 ssh(1). ssh-keygen can create keys for use by SSH protocol versions 1 35 and 2. Protocol 1 should not be used and is only offered to support 36 legacy devices. It suffers from a number of cryptographic weaknesses and 37 doesn't support many of the advanced features available for protocol 2. 38 39 The type of key to be generated is specified with the -t option. If 40 invoked without any arguments, ssh-keygen will generate an RSA key for 41 use in SSH protocol 2 connections. 42 43 ssh-keygen is also used to generate groups for use in Diffie-Hellman 44 group exchange (DH-GEX). See the MODULI GENERATION section for details. 45 46 Finally, ssh-keygen can be used to generate and update Key Revocation 47 Lists, and to test whether given keys have been revoked by one. See the 48 KEY REVOCATION LISTS section for details. 49 50 Normally each user wishing to use SSH with public key authentication runs 51 this once to create the authentication key in ~/.ssh/identity, 52 ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 or ~/.ssh/id_rsa. 53 Additionally, the system administrator may use this to generate host 54 keys, as seen in /etc/rc. 55 56 Normally this program generates the key and asks for a file in which to 57 store the private key. The public key is stored in a file with the same 58 name but M-bM-^@M-^\.pubM-bM-^@M-^] appended. The program also asks for a passphrase. The 59 passphrase may be empty to indicate no passphrase (host keys must have an 60 empty passphrase), or it may be a string of arbitrary length. A 61 passphrase is similar to a password, except it can be a phrase with a 62 series of words, punctuation, numbers, whitespace, or any string of 63 characters you want. Good passphrases are 10-30 characters long, are not 64 simple sentences or otherwise easily guessable (English prose has only 65 1-2 bits of entropy per character, and provides very bad passphrases), 66 and contain a mix of upper and lowercase letters, numbers, and non- 67 alphanumeric characters. The passphrase can be changed later by using 68 the -p option. 69 70 There is no way to recover a lost passphrase. If the passphrase is lost 71 or forgotten, a new key must be generated and the corresponding public 72 key copied to other machines. 73 74 For RSA1 keys and keys stored in the newer OpenSSH format, there is also 75 a comment field in the key file that is only for convenience to the user 76 to help identify the key. The comment can tell what the key is for, or 77 whatever is useful. The comment is initialized to M-bM-^@M-^\user@hostM-bM-^@M-^] when the 78 key is created, but can be changed using the -c option. 79 80 After a key is generated, instructions below detail where the keys should 81 be placed to be activated. 82 83 The options are as follows: 84 85 -A For each of the key types (rsa1, rsa, dsa, ecdsa and ed25519) for 86 which host keys do not exist, generate the host keys with the 87 default key file path, an empty passphrase, default bits for the 88 key type, and default comment. This is used by /etc/rc to 89 generate new host keys. 90 91 -a rounds 92 When saving a new-format private key (i.e. an ed25519 key or any 93 SSH protocol 2 key when the -o flag is set), this option 94 specifies the number of KDF (key derivation function) rounds 95 used. Higher numbers result in slower passphrase verification 96 and increased resistance to brute-force password cracking (should 97 the keys be stolen). 98 99 When screening DH-GEX candidates ( using the -T command). This 100 option specifies the number of primality tests to perform. 101 102 -B Show the bubblebabble digest of specified private or public key 103 file. 104 105 -b bits 106 Specifies the number of bits in the key to create. For RSA keys, 107 the minimum size is 1024 bits and the default is 2048 bits. 108 Generally, 2048 bits is considered sufficient. DSA keys must be 109 exactly 1024 bits as specified by FIPS 186-2. For ECDSA keys, 110 the -b flag determines the key length by selecting from one of 111 three elliptic curve sizes: 256, 384 or 521 bits. Attempting to 112 use bit lengths other than these three values for ECDSA keys will 113 fail. Ed25519 keys have a fixed length and the -b flag will be 114 ignored. 115 116 -C comment 117 Provides a new comment. 118 119 -c Requests changing the comment in the private and public key 120 files. This operation is only supported for RSA1 keys and keys 121 stored in the newer OpenSSH format. The program will prompt for 122 the file containing the private keys, for the passphrase if the 123 key has one, and for the new comment. 124 125 -D pkcs11 126 Download the RSA public keys provided by the PKCS#11 shared 127 library pkcs11. When used in combination with -s, this option 128 indicates that a CA key resides in a PKCS#11 token (see the 129 CERTIFICATES section for details). 130 131 -E fingerprint_hash 132 Specifies the hash algorithm used when displaying key 133 fingerprints. Valid options are: M-bM-^@M-^\md5M-bM-^@M-^] and M-bM-^@M-^\sha256M-bM-^@M-^]. The 134 default is M-bM-^@M-^\sha256M-bM-^@M-^]. 135 136 -e This option will read a private or public OpenSSH key file and 137 print to stdout the key in one of the formats specified by the -m 138 option. The default export format is M-bM-^@M-^\RFC4716M-bM-^@M-^]. This option 139 allows exporting OpenSSH keys for use by other programs, 140 including several commercial SSH implementations. 141 142 -F hostname 143 Search for the specified hostname in a known_hosts file, listing 144 any occurrences found. This option is useful to find hashed host 145 names or addresses and may also be used in conjunction with the 146 -H option to print found keys in a hashed format. 147 148 -f filename 149 Specifies the filename of the key file. 150 151 -G output_file 152 Generate candidate primes for DH-GEX. These primes must be 153 screened for safety (using the -T option) before use. 154 155 -g Use generic DNS format when printing fingerprint resource records 156 using the -r command. 157 158 -H Hash a known_hosts file. This replaces all hostnames and 159 addresses with hashed representations within the specified file; 160 the original content is moved to a file with a .old suffix. 161 These hashes may be used normally by ssh and sshd, but they do 162 not reveal identifying information should the file's contents be 163 disclosed. This option will not modify existing hashed hostnames 164 and is therefore safe to use on files that mix hashed and non- 165 hashed names. 166 167 -h When signing a key, create a host certificate instead of a user 168 certificate. Please see the CERTIFICATES section for details. 169 170 -I certificate_identity 171 Specify the key identity when signing a public key. Please see 172 the CERTIFICATES section for details. 173 174 -i This option will read an unencrypted private (or public) key file 175 in the format specified by the -m option and print an OpenSSH 176 compatible private (or public) key to stdout. This option allows 177 importing keys from other software, including several commercial 178 SSH implementations. The default import format is M-bM-^@M-^\RFC4716M-bM-^@M-^]. 179 180 -J num_lines 181 Exit after screening the specified number of lines while 182 performing DH candidate screening using the -T option. 183 184 -j start_line 185 Start screening at the specified line number while performing DH 186 candidate screening using the -T option. 187 188 -K checkpt 189 Write the last line processed to the file checkpt while 190 performing DH candidate screening using the -T option. This will 191 be used to skip lines in the input file that have already been 192 processed if the job is restarted. 193 194 -k Generate a KRL file. In this mode, ssh-keygen will generate a 195 KRL file at the location specified via the -f flag that revokes 196 every key or certificate presented on the command line. 197 Keys/certificates to be revoked may be specified by public key 198 file or using the format described in the KEY REVOCATION LISTS 199 section. 200 201 -L Prints the contents of one or more certificates. 202 203 -l Show fingerprint of specified public key file. Private RSA1 keys 204 are also supported. For RSA and DSA keys ssh-keygen tries to 205 find the matching public key file and prints its fingerprint. If 206 combined with -v, a visual ASCII art representation of the key is 207 supplied with the fingerprint. 208 209 -M memory 210 Specify the amount of memory to use (in megabytes) when 211 generating candidate moduli for DH-GEX. 212 213 -m key_format 214 Specify a key format for the -i (import) or -e (export) 215 conversion options. The supported key formats are: M-bM-^@M-^\RFC4716M-bM-^@M-^] 216 (RFC 4716/SSH2 public or private key), M-bM-^@M-^\PKCS8M-bM-^@M-^] (PEM PKCS8 public 217 key) or M-bM-^@M-^\PEMM-bM-^@M-^] (PEM public key). The default conversion format is 218 M-bM-^@M-^\RFC4716M-bM-^@M-^]. 219 220 -N new_passphrase 221 Provides the new passphrase. 222 223 -n principals 224 Specify one or more principals (user or host names) to be 225 included in a certificate when signing a key. Multiple 226 principals may be specified, separated by commas. Please see the 227 CERTIFICATES section for details. 228 229 -O option 230 Specify a certificate option when signing a key. This option may 231 be specified multiple times. Please see the CERTIFICATES section 232 for details. The options that are valid for user certificates 233 are: 234 235 clear Clear all enabled permissions. This is useful for 236 clearing the default set of permissions so permissions 237 may be added individually. 238 239 force-command=command 240 Forces the execution of command instead of any shell or 241 command specified by the user when the certificate is 242 used for authentication. 243 244 no-agent-forwarding 245 Disable ssh-agent(1) forwarding (permitted by default). 246 247 no-port-forwarding 248 Disable port forwarding (permitted by default). 249 250 no-pty Disable PTY allocation (permitted by default). 251 252 no-user-rc 253 Disable execution of ~/.ssh/rc by sshd(8) (permitted by 254 default). 255 256 no-x11-forwarding 257 Disable X11 forwarding (permitted by default). 258 259 permit-agent-forwarding 260 Allows ssh-agent(1) forwarding. 261 262 permit-port-forwarding 263 Allows port forwarding. 264 265 permit-pty 266 Allows PTY allocation. 267 268 permit-user-rc 269 Allows execution of ~/.ssh/rc by sshd(8). 270 271 permit-x11-forwarding 272 Allows X11 forwarding. 273 274 source-address=address_list 275 Restrict the source addresses from which the certificate 276 is considered valid. The address_list is a comma- 277 separated list of one or more address/netmask pairs in 278 CIDR format. 279 280 At present, no options are valid for host keys. 281 282 -o Causes ssh-keygen to save private keys using the new OpenSSH 283 format rather than the more compatible PEM format. The new 284 format has increased resistance to brute-force password cracking 285 but is not supported by versions of OpenSSH prior to 6.5. 286 Ed25519 keys always use the new private key format. 287 288 -P passphrase 289 Provides the (old) passphrase. 290 291 -p Requests changing the passphrase of a private key file instead of 292 creating a new private key. The program will prompt for the file 293 containing the private key, for the old passphrase, and twice for 294 the new passphrase. 295 296 -Q Test whether keys have been revoked in a KRL. 297 298 -q Silence ssh-keygen. 299 300 -R hostname 301 Removes all keys belonging to hostname from a known_hosts file. 302 This option is useful to delete hashed hosts (see the -H option 303 above). 304 305 -r hostname 306 Print the SSHFP fingerprint resource record named hostname for 307 the specified public key file. 308 309 -S start 310 Specify start point (in hex) when generating candidate moduli for 311 DH-GEX. 312 313 -s ca_key 314 Certify (sign) a public key using the specified CA key. Please 315 see the CERTIFICATES section for details. 316 317 When generating a KRL, -s specifies a path to a CA public key 318 file used to revoke certificates directly by key ID or serial 319 number. See the KEY REVOCATION LISTS section for details. 320 321 -T output_file 322 Test DH group exchange candidate primes (generated using the -G 323 option) for safety. 324 325 -t dsa | ecdsa | ed25519 | rsa | rsa1 326 Specifies the type of key to create. The possible values are 327 M-bM-^@M-^\rsa1M-bM-^@M-^] for protocol version 1 and M-bM-^@M-^\dsaM-bM-^@M-^], M-bM-^@M-^\ecdsaM-bM-^@M-^], M-bM-^@M-^\ed25519M-bM-^@M-^], or 328 M-bM-^@M-^\rsaM-bM-^@M-^] for protocol version 2. 329 330 -u Update a KRL. When specified with -k, keys listed via the 331 command line are added to the existing KRL rather than a new KRL 332 being created. 333 334 -V validity_interval 335 Specify a validity interval when signing a certificate. A 336 validity interval may consist of a single time, indicating that 337 the certificate is valid beginning now and expiring at that time, 338 or may consist of two times separated by a colon to indicate an 339 explicit time interval. The start time may be specified as a 340 date in YYYYMMDD format, a time in YYYYMMDDHHMMSS format or a 341 relative time (to the current time) consisting of a minus sign 342 followed by a relative time in the format described in the TIME 343 FORMATS section of sshd_config(5). The end time may be specified 344 as a YYYYMMDD date, a YYYYMMDDHHMMSS time or a relative time 345 starting with a plus character. 346 347 For example: M-bM-^@M-^\+52w1dM-bM-^@M-^] (valid from now to 52 weeks and one day 348 from now), M-bM-^@M-^\-4w:+4wM-bM-^@M-^] (valid from four weeks ago to four weeks 349 from now), M-bM-^@M-^\20100101123000:20110101123000M-bM-^@M-^] (valid from 12:30 PM, 350 January 1st, 2010 to 12:30 PM, January 1st, 2011), M-bM-^@M-^\-1d:20110101M-bM-^@M-^] 351 (valid from yesterday to midnight, January 1st, 2011). 352 353 -v Verbose mode. Causes ssh-keygen to print debugging messages 354 about its progress. This is helpful for debugging moduli 355 generation. Multiple -v options increase the verbosity. The 356 maximum is 3. 357 358 -W generator 359 Specify desired generator when testing candidate moduli for DH- 360 GEX. 361 362 -y This option will read a private OpenSSH format file and print an 363 OpenSSH public key to stdout. 364 365 -z serial_number 366 Specifies a serial number to be embedded in the certificate to 367 distinguish this certificate from others from the same CA. The 368 default serial number is zero. 369 370 When generating a KRL, the -z flag is used to specify a KRL 371 version number. 372 373 MODULI GENERATION 374 ssh-keygen may be used to generate groups for the Diffie-Hellman Group 375 Exchange (DH-GEX) protocol. Generating these groups is a two-step 376 process: first, candidate primes are generated using a fast, but memory 377 intensive process. These candidate primes are then tested for 378 suitability (a CPU-intensive process). 379 380 Generation of primes is performed using the -G option. The desired 381 length of the primes may be specified by the -b option. For example: 382 383 # ssh-keygen -G moduli-2048.candidates -b 2048 384 385 By default, the search for primes begins at a random point in the desired 386 length range. This may be overridden using the -S option, which 387 specifies a different start point (in hex). 388 389 Once a set of candidates have been generated, they must be screened for 390 suitability. This may be performed using the -T option. In this mode 391 ssh-keygen will read candidates from standard input (or a file specified 392 using the -f option). For example: 393 394 # ssh-keygen -T moduli-2048 -f moduli-2048.candidates 395 396 By default, each candidate will be subjected to 100 primality tests. 397 This may be overridden using the -a option. The DH generator value will 398 be chosen automatically for the prime under consideration. If a specific 399 generator is desired, it may be requested using the -W option. Valid 400 generator values are 2, 3, and 5. 401 402 Screened DH groups may be installed in /etc/moduli. It is important that 403 this file contains moduli of a range of bit lengths and that both ends of 404 a connection share common moduli. 405 406 CERTIFICATES 407 ssh-keygen supports signing of keys to produce certificates that may be 408 used for user or host authentication. Certificates consist of a public 409 key, some identity information, zero or more principal (user or host) 410 names and a set of options that are signed by a Certification Authority 411 (CA) key. Clients or servers may then trust only the CA key and verify 412 its signature on a certificate rather than trusting many user/host keys. 413 Note that OpenSSH certificates are a different, and much simpler, format 414 to the X.509 certificates used in ssl(8). 415 416 ssh-keygen supports two types of certificates: user and host. User 417 certificates authenticate users to servers, whereas host certificates 418 authenticate server hosts to users. To generate a user certificate: 419 420 $ ssh-keygen -s /path/to/ca_key -I key_id /path/to/user_key.pub 421 422 The resultant certificate will be placed in /path/to/user_key-cert.pub. 423 A host certificate requires the -h option: 424 425 $ ssh-keygen -s /path/to/ca_key -I key_id -h /path/to/host_key.pub 426 427 The host certificate will be output to /path/to/host_key-cert.pub. 428 429 It is possible to sign using a CA key stored in a PKCS#11 token by 430 providing the token library using -D and identifying the CA key by 431 providing its public half as an argument to -s: 432 433 $ ssh-keygen -s ca_key.pub -D libpkcs11.so -I key_id user_key.pub 434 435 In all cases, key_id is a "key identifier" that is logged by the server 436 when the certificate is used for authentication. 437 438 Certificates may be limited to be valid for a set of principal 439 (user/host) names. By default, generated certificates are valid for all 440 users or hosts. To generate a certificate for a specified set of 441 principals: 442 443 $ ssh-keygen -s ca_key -I key_id -n user1,user2 user_key.pub 444 $ ssh-keygen -s ca_key -I key_id -h -n host.domain host_key.pub 445 446 Additional limitations on the validity and use of user certificates may 447 be specified through certificate options. A certificate option may 448 disable features of the SSH session, may be valid only when presented 449 from particular source addresses or may force the use of a specific 450 command. For a list of valid certificate options, see the documentation 451 for the -O option above. 452 453 Finally, certificates may be defined with a validity lifetime. The -V 454 option allows specification of certificate start and end times. A 455 certificate that is presented at a time outside this range will not be 456 considered valid. By default, certificates are valid from UNIX Epoch to 457 the distant future. 458 459 For certificates to be used for user or host authentication, the CA 460 public key must be trusted by sshd(8) or ssh(1). Please refer to those 461 manual pages for details. 462 463 KEY REVOCATION LISTS 464 ssh-keygen is able to manage OpenSSH format Key Revocation Lists (KRLs). 465 These binary files specify keys or certificates to be revoked using a 466 compact format, taking as little as one bit per certificate if they are 467 being revoked by serial number. 468 469 KRLs may be generated using the -k flag. This option reads one or more 470 files from the command line and generates a new KRL. The files may 471 either contain a KRL specification (see below) or public keys, listed one 472 per line. Plain public keys are revoked by listing their hash or 473 contents in the KRL and certificates revoked by serial number or key ID 474 (if the serial is zero or not available). 475 476 Revoking keys using a KRL specification offers explicit control over the 477 types of record used to revoke keys and may be used to directly revoke 478 certificates by serial number or key ID without having the complete 479 original certificate on hand. A KRL specification consists of lines 480 containing one of the following directives followed by a colon and some 481 directive-specific information. 482 483 serial: serial_number[-serial_number] 484 Revokes a certificate with the specified serial number. Serial 485 numbers are 64-bit values, not including zero and may be 486 expressed in decimal, hex or octal. If two serial numbers are 487 specified separated by a hyphen, then the range of serial numbers 488 including and between each is revoked. The CA key must have been 489 specified on the ssh-keygen command line using the -s option. 490 491 id: key_id 492 Revokes a certificate with the specified key ID string. The CA 493 key must have been specified on the ssh-keygen command line using 494 the -s option. 495 496 key: public_key 497 Revokes the specified key. If a certificate is listed, then it 498 is revoked as a plain public key. 499 500 sha1: public_key 501 Revokes the specified key by its SHA1 hash. 502 503 KRLs may be updated using the -u flag in addition to -k. When this 504 option is specified, keys listed via the command line are merged into the 505 KRL, adding to those already there. 506 507 It is also possible, given a KRL, to test whether it revokes a particular 508 key (or keys). The -Q flag will query an existing KRL, testing each key 509 specified on the command line. If any key listed on the command line has 510 been revoked (or an error encountered) then ssh-keygen will exit with a 511 non-zero exit status. A zero exit status will only be returned if no key 512 was revoked. 513 514 FILES 515 ~/.ssh/identity 516 Contains the protocol version 1 RSA authentication identity of 517 the user. This file should not be readable by anyone but the 518 user. It is possible to specify a passphrase when generating the 519 key; that passphrase will be used to encrypt the private part of 520 this file using 3DES. This file is not automatically accessed by 521 ssh-keygen but it is offered as the default file for the private 522 key. ssh(1) will read this file when a login attempt is made. 523 524 ~/.ssh/identity.pub 525 Contains the protocol version 1 RSA public key for 526 authentication. The contents of this file should be added to 527 ~/.ssh/authorized_keys on all machines where the user wishes to 528 log in using RSA authentication. There is no need to keep the 529 contents of this file secret. 530 531 ~/.ssh/id_dsa 532 ~/.ssh/id_ecdsa 533 ~/.ssh/id_ed25519 534 ~/.ssh/id_rsa 535 Contains the protocol version 2 DSA, ECDSA, Ed25519 or RSA 536 authentication identity of the user. This file should not be 537 readable by anyone but the user. It is possible to specify a 538 passphrase when generating the key; that passphrase will be used 539 to encrypt the private part of this file using 128-bit AES. This 540 file is not automatically accessed by ssh-keygen but it is 541 offered as the default file for the private key. ssh(1) will 542 read this file when a login attempt is made. 543 544 ~/.ssh/id_dsa.pub 545 ~/.ssh/id_ecdsa.pub 546 ~/.ssh/id_ed25519.pub 547 ~/.ssh/id_rsa.pub 548 Contains the protocol version 2 DSA, ECDSA, Ed25519 or RSA public 549 key for authentication. The contents of this file should be 550 added to ~/.ssh/authorized_keys on all machines where the user 551 wishes to log in using public key authentication. There is no 552 need to keep the contents of this file secret. 553 554 /etc/moduli 555 Contains Diffie-Hellman groups used for DH-GEX. The file format 556 is described in moduli(5). 557 558 SEE ALSO 559 ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8) 560 561 The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006. 562 563 AUTHORS 564 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 565 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 566 de Raadt and Dug Song removed many bugs, re-added newer features and 567 created OpenSSH. Markus Friedl contributed the support for SSH protocol 568 versions 1.5 and 2.0. 569 570 OpenBSD 6.0 June 16, 2016 OpenBSD 6.0 571
