ssh-keygen.0 revision 189006
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 [-f input_keyfile] 11 ssh-keygen -e [-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 reader 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 -U reader [-f input_keyfile] 21 ssh-keygen -r hostname [-f input_keyfile] [-g] 22 ssh-keygen -G output_file [-v] [-b bits] [-M memory] [-S start_point] 23 ssh-keygen -T output_file -f input_file [-v] [-a num_trials] [-W 24 generator] 25 26DESCRIPTION 27 ssh-keygen generates, manages and converts authentication keys for 28 ssh(1). ssh-keygen can create RSA keys for use by SSH protocol version 1 29 and RSA or DSA keys for use by SSH protocol version 2. The type of key 30 to be generated is specified with the -t option. If invoked without any 31 arguments, ssh-keygen will generate an RSA key for use in SSH protocol 2 32 connections. 33 34 ssh-keygen is also used to generate groups for use in Diffie-Hellman 35 group exchange (DH-GEX). See the MODULI GENERATION section for details. 36 37 Normally each user wishing to use SSH with RSA or DSA authentication runs 38 this once to create the authentication key in ~/.ssh/identity, 39 ~/.ssh/id_dsa or ~/.ssh/id_rsa. Additionally, the system administrator 40 may use this to generate host keys, as seen in /etc/rc. 41 42 Normally this program generates the key and asks for a file in which to 43 store the private key. The public key is stored in a file with the same 44 name but ``.pub'' appended. The program also asks for a passphrase. The 45 passphrase may be empty to indicate no passphrase (host keys must have an 46 empty passphrase), or it may be a string of arbitrary length. A 47 passphrase is similar to a password, except it can be a phrase with a se- 48 ries of words, punctuation, numbers, whitespace, or any string of charac- 49 ters you want. Good passphrases are 10-30 characters long, are not sim- 50 ple sentences or otherwise easily guessable (English prose has only 1-2 51 bits of entropy per character, and provides very bad passphrases), and 52 contain a mix of upper and lowercase letters, numbers, and non-alphanu- 53 meric characters. The passphrase can be changed later by using the -p 54 option. 55 56 There is no way to recover a lost passphrase. If the passphrase is lost 57 or forgotten, a new key must be generated and copied to the corresponding 58 public key to other machines. 59 60 For RSA1 keys, there is also a comment field in the key file that is only 61 for convenience to the user to help identify the key. The comment can 62 tell what the key is for, or whatever is useful. The comment is initial- 63 ized to ``user@host'' when the key is created, but can be changed using 64 the -c option. 65 66 After a key is generated, instructions below detail where the keys should 67 be placed to be activated. 68 69 The options are as follows: 70 71 -a trials 72 Specifies the number of primality tests to perform when screening 73 DH-GEX candidates using the -T command. 74 75 -B Show the bubblebabble digest of specified private or public key 76 file. 77 78 -b bits 79 Specifies the number of bits in the key to create. For RSA keys, 80 the minimum size is 768 bits and the default is 2048 bits. Gen- 81 erally, 2048 bits is considered sufficient. DSA keys must be ex- 82 actly 1024 bits as specified by FIPS 186-2. 83 84 -C comment 85 Provides a new comment. 86 87 -c Requests changing the comment in the private and public key 88 files. This operation is only supported for RSA1 keys. The pro- 89 gram will prompt for the file containing the private keys, for 90 the passphrase if the key has one, and for the new comment. 91 92 -D reader 93 Download the RSA public key stored in the smartcard in reader. 94 95 -e This option will read a private or public OpenSSH key file and 96 print the key in RFC 4716 SSH Public Key File Format to stdout. 97 This option allows exporting keys for use by several commercial 98 SSH implementations. 99 100 -F hostname 101 Search for the specified hostname in a known_hosts file, listing 102 any occurrences found. This option is useful to find hashed host 103 names or addresses and may also be used in conjunction with the 104 -H option to print found keys in a hashed format. 105 106 -f filename 107 Specifies the filename of the key file. 108 109 -G output_file 110 Generate candidate primes for DH-GEX. These primes must be 111 screened for safety (using the -T option) before use. 112 113 -g Use generic DNS format when printing fingerprint resource records 114 using the -r command. 115 116 -H Hash a known_hosts file. This replaces all hostnames and ad- 117 dresses with hashed representations within the specified file; 118 the original content is moved to a file with a .old suffix. 119 These hashes may be used normally by ssh and sshd, but they do 120 not reveal identifying information should the file's contents be 121 disclosed. This option will not modify existing hashed hostnames 122 and is therefore safe to use on files that mix hashed and non- 123 hashed names. 124 125 -i This option will read an unencrypted private (or public) key file 126 in SSH2-compatible format and print an OpenSSH compatible private 127 (or public) key to stdout. ssh-keygen also reads the RFC 4716 128 SSH Public Key File Format. This option allows importing keys 129 from several commercial SSH implementations. 130 131 -l Show fingerprint of specified public key file. Private RSA1 keys 132 are also supported. For RSA and DSA keys ssh-keygen tries to 133 find the matching public key file and prints its fingerprint. If 134 combined with -v, an ASCII art representation of the key is sup- 135 plied with the fingerprint. 136 137 -M memory 138 Specify the amount of memory to use (in megabytes) when generat- 139 ing candidate moduli for DH-GEX. 140 141 -N new_passphrase 142 Provides the new passphrase. 143 144 -P passphrase 145 Provides the (old) passphrase. 146 147 -p Requests changing the passphrase of a private key file instead of 148 creating a new private key. The program will prompt for the file 149 containing the private key, for the old passphrase, and twice for 150 the new passphrase. 151 152 -q Silence ssh-keygen. Used by /etc/rc when creating a new key. 153 154 -R hostname 155 Removes all keys belonging to hostname from a known_hosts file. 156 This option is useful to delete hashed hosts (see the -H option 157 above). 158 159 -r hostname 160 Print the SSHFP fingerprint resource record named hostname for 161 the specified public key file. 162 163 -S start 164 Specify start point (in hex) when generating candidate moduli for 165 DH-GEX. 166 167 -T output_file 168 Test DH group exchange candidate primes (generated using the -G 169 option) for safety. 170 171 -t type 172 Specifies the type of key to create. The possible values are 173 ``rsa1'' for protocol version 1 and ``rsa'' or ``dsa'' for proto- 174 col version 2. 175 176 -U reader 177 Upload an existing RSA private key into the smartcard in reader. 178 179 -v Verbose mode. Causes ssh-keygen to print debugging messages 180 about its progress. This is helpful for debugging moduli genera- 181 tion. Multiple -v options increase the verbosity. The maximum 182 is 3. 183 184 -W generator 185 Specify desired generator when testing candidate moduli for DH- 186 GEX. 187 188 -y This option will read a private OpenSSH format file and print an 189 OpenSSH public key to stdout. 190 191MODULI GENERATION 192 ssh-keygen may be used to generate groups for the Diffie-Hellman Group 193 Exchange (DH-GEX) protocol. Generating these groups is a two-step pro- 194 cess: first, candidate primes are generated using a fast, but memory in- 195 tensive process. These candidate primes are then tested for suitability 196 (a CPU-intensive process). 197 198 Generation of primes is performed using the -G option. The desired 199 length of the primes may be specified by the -b option. For example: 200 201 # ssh-keygen -G moduli-2048.candidates -b 2048 202 203 By default, the search for primes begins at a random point in the desired 204 length range. This may be overridden using the -S option, which speci- 205 fies a different start point (in hex). 206 207 Once a set of candidates have been generated, they must be tested for 208 suitability. This may be performed using the -T option. In this mode 209 ssh-keygen will read candidates from standard input (or a file specified 210 using the -f option). For example: 211 212 # ssh-keygen -T moduli-2048 -f moduli-2048.candidates 213 214 By default, each candidate will be subjected to 100 primality tests. 215 This may be overridden using the -a option. The DH generator value will 216 be chosen automatically for the prime under consideration. If a specific 217 generator is desired, it may be requested using the -W option. Valid 218 generator values are 2, 3, and 5. 219 220 Screened DH groups may be installed in /etc/moduli. It is important that 221 this file contains moduli of a range of bit lengths and that both ends of 222 a connection share common moduli. 223 224FILES 225 ~/.ssh/identity 226 Contains the protocol version 1 RSA authentication identity of 227 the user. This file should not be readable by anyone but the us- 228 er. It is possible to specify a passphrase when generating the 229 key; that passphrase will be used to encrypt the private part of 230 this file using 3DES. This file is not automatically accessed by 231 ssh-keygen but it is offered as the default file for the private 232 key. ssh(1) will read this file when a login attempt is made. 233 234 ~/.ssh/identity.pub 235 Contains the protocol version 1 RSA public key for authentica- 236 tion. The contents of this file should be added to 237 ~/.ssh/authorized_keys on all machines where the user wishes to 238 log in using RSA authentication. There is no need to keep the 239 contents of this file secret. 240 241 ~/.ssh/id_dsa 242 Contains the protocol version 2 DSA authentication identity of 243 the user. This file should not be readable by anyone but the us- 244 er. It is possible to specify a passphrase when generating the 245 key; that passphrase will be used to encrypt the private part of 246 this file using 3DES. This file is not automatically accessed by 247 ssh-keygen but it is offered as the default file for the private 248 key. ssh(1) will read this file when a login attempt is made. 249 250 ~/.ssh/id_dsa.pub 251 Contains the protocol version 2 DSA public key for authentica- 252 tion. The contents of this file should be added to 253 ~/.ssh/authorized_keys on all machines where the user wishes to 254 log in using public key authentication. There is no need to keep 255 the contents of this file secret. 256 257 ~/.ssh/id_rsa 258 Contains the protocol version 2 RSA authentication identity of 259 the user. This file should not be readable by anyone but the us- 260 er. It is possible to specify a passphrase when generating the 261 key; that passphrase will be used to encrypt the private part of 262 this file using 3DES. This file is not automatically accessed by 263 ssh-keygen but it is offered as the default file for the private 264 key. ssh(1) will read this file when a login attempt is made. 265 266 ~/.ssh/id_rsa.pub 267 Contains the protocol version 2 RSA public key for authentica- 268 tion. The contents of this file should be added to 269 ~/.ssh/authorized_keys on all machines where the user wishes to 270 log in using public key authentication. There is no need to keep 271 the contents of this file secret. 272 273 /etc/moduli 274 Contains Diffie-Hellman groups used for DH-GEX. The file format 275 is described in moduli(5). 276 277SEE ALSO 278 ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8) 279 280 The Secure Shell (SSH) Public Key File Format, RFC 4716, 2006. 281 282AUTHORS 283 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 284 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 285 de Raadt and Dug Song removed many bugs, re-added newer features and 286 created OpenSSH. Markus Friedl contributed the support for SSH protocol 287 versions 1.5 and 2.0. 288 289OpenBSD 4.5 July 24, 2008 5 290