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authorColin Watson <cjwatson@debian.org>2005-05-30 21:44:32 +0000
committerColin Watson <cjwatson@debian.org>2005-05-30 21:44:32 +0000
commita55bd782aa819b7f5ae716de000f19f4f531850e (patch)
tree12638b19bc0ed9c8d48541d460693ab0fbb58e89 /ssh-keygen.0
parentfe9489f7e522f780f3fa5c2f28208124d193398c (diff)
parent5d05471f6657646d1d6500c7c43134462c407ee6 (diff)
Import OpenSSH 4.1p1.
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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]
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.
31
32 ssh-keygen is also used to generate groups for use in Diffie-Hellman
33 group exchange (DH-GEX). See the MODULI GENERATION section for details.
34
35 Normally each user wishing to use SSH with RSA or DSA authentication runs
36 this once to create the authentication key in $HOME/.ssh/identity,
37 $HOME/.ssh/id_dsa or $HOME/.ssh/id_rsa. Additionally, the system admin-
38 istrator may use this to generate host keys, as seen in /etc/rc.
39
40 Normally this program generates the key and asks for a file in which to
41 store the private key. The public key is stored in a file with the same
42 name but ``.pub'' appended. The program also asks for a passphrase. The
43 passphrase may be empty to indicate no passphrase (host keys must have an
44 empty passphrase), or it may be a string of arbitrary length. A
45 passphrase is similar to a password, except it can be a phrase with a se-
46 ries of words, punctuation, numbers, whitespace, or any string of charac-
47 ters you want. Good passphrases are 10-30 characters long, are not sim-
48 ple sentences or otherwise easily guessable (English prose has only 1-2
49 bits of entropy per character, and provides very bad passphrases), and
50 contain a mix of upper and lowercase letters, numbers, and non-alphanu-
51 meric characters. The passphrase can be changed later by using the -p
52 option.
53
54 There is no way to recover a lost passphrase. If the passphrase is lost
55 or forgotten, a new key must be generated and copied to the corresponding
56 public key to other machines.
57
58 For RSA1 keys, there is also a comment field in the key file that is only
59 for convenience to the user to help identify the key. The comment can
60 tell what the key is for, or whatever is useful. The comment is initial-
61 ized to ``user@host'' when the key is created, but can be changed using
62 the -c option.
63
64 After a key is generated, instructions below detail where the keys should
65 be placed to be activated.
66
67 The options are as follows:
68
69 -a trials
70 Specifies the number of primality tests to perform when screening
71 DH-GEX candidates using the -T command.
72
73 -B Show the bubblebabble digest of specified private or public key
74 file.
75
76 -b bits
77 Specifies the number of bits in the key to create. Minimum is
78 512 bits. Generally, 1024 bits is considered sufficient. The
79 default is 1024 bits.
80
81 -C comment
82 Provides a new comment.
83
84 -c Requests changing the comment in the private and public key
85 files. This operation is only supported for RSA1 keys. The pro-
86 gram will prompt for the file containing the private keys, for
87 the passphrase if the key has one, and for the new comment.
88
89 -D reader
90 Download the RSA public key stored in the smartcard in reader.
91
92 -e This option will read a private or public OpenSSH key file and
93 print the key in a `SECSH Public Key File Format' to stdout.
94 This option allows exporting keys for use by several commercial
95 SSH implementations.
96
97 -F hostname
98 Search for the specified hostname in a known_hosts file, listing
99 any occurrences found. This option is useful to find hashed host
100 names or addresses and may also be used in conjunction with the
101 -H option to print found keys in a hashed format.
102
103 -f filename
104 Specifies the filename of the key file.
105
106 -G output_file
107 Generate candidate primes for DH-GEX. These primes must be
108 screened for safety (using the -T option) before use.
109
110 -g Use generic DNS format when printing fingerprint resource records
111 using the -r command.
112
113 -H Hash a known_hosts file. This replaces all hostnames and ad-
114 dresses with hashed representations within the specified file;
115 the original content is moved to a file with a .old suffix.
116 These hashes may be used normally by ssh and sshd, but they do
117 not reveal identifying information should the file's contents be
118 disclosed. This option will not modify existing hashed hostnames
119 and is therefore safe to use on files that mix hashed and non-
120 hashed names.
121
122 -i This option will read an unencrypted private (or public) key file
123 in SSH2-compatible format and print an OpenSSH compatible private
124 (or public) key to stdout. ssh-keygen also reads the `SECSH
125 Public Key File Format'. This option allows importing keys from
126 several commercial SSH implementations.
127
128 -l Show fingerprint of specified public key file. Private RSA1 keys
129 are also supported. For RSA and DSA keys ssh-keygen tries to
130 find the matching public key file and prints its fingerprint.
131
132 -M memory
133 Specify the amount of memory to use (in megabytes) when generat-
134 ing candidate moduli for DH-GEX.
135
136 -N new_passphrase
137 Provides the new passphrase.
138
139 -P passphrase
140 Provides the (old) passphrase.
141
142 -p Requests changing the passphrase of a private key file instead of
143 creating a new private key. The program will prompt for the file
144 containing the private key, for the old passphrase, and twice for
145 the new passphrase.
146
147 -q Silence ssh-keygen. Used by /etc/rc when creating a new key.
148
149 -R hostname
150 Removes all keys belonging to hostname from a known_hosts file.
151 This option is useful to delete hashed hosts (see the -H option
152 above).
153
154 -r hostname
155 Print the SSHFP fingerprint resource record named hostname for
156 the specified public key file.
157
158 -S start
159 Specify start point (in hex) when generating candidate moduli for
160 DH-GEX.
161
162 -T output_file
163 Test DH group exchange candidate primes (generated using the -G
164 option) for safety.
165
166 -t type
167 Specifies the type of key to create. The possible values are
168 ``rsa1'' for protocol version 1 and ``rsa'' or ``dsa'' for proto-
169 col version 2.
170
171 -U reader
172 Upload an existing RSA private key into the smartcard in reader.
173
174 -v Verbose mode. Causes ssh-keygen to print debugging messages
175 about its progress. This is helpful for debugging moduli genera-
176 tion. Multiple -v options increase the verbosity. The maximum
177 is 3.
178
179 -W generator
180 Specify desired generator when testing candidate moduli for DH-
181 GEX.
182
183 -y This option will read a private OpenSSH format file and print an
184 OpenSSH public key to stdout.
185
186MODULI GENERATION
187 ssh-keygen may be used to generate groups for the Diffie-Hellman Group
188 Exchange (DH-GEX) protocol. Generating these groups is a two-step pro-
189 cess: first, candidate primes are generated using a fast, but memory in-
190 tensive process. These candidate primes are then tested for suitability
191 (a CPU-intensive process).
192
193 Generation of primes is performed using the -G option. The desired
194 length of the primes may be specified by the -b option. For example:
195
196 # ssh-keygen -G moduli-2048.candidates -b 2048
197
198 By default, the search for primes begins at a random point in the desired
199 length range. This may be overridden using the -S option, which speci-
200 fies a different start point (in hex).
201
202 Once a set of candidates have been generated, they must be tested for
203 suitability. This may be performed using the -T option. In this mode
204 ssh-keygen will read candidates from standard input (or a file specified
205 using the -f option). For example:
206
207 # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
208
209 By default, each candidate will be subjected to 100 primality tests.
210 This may be overridden using the -a option. The DH generator value will
211 be chosen automatically for the prime under consideration. If a specific
212 generator is desired, it may be requested using the -W option. Valid
213 generator values are 2, 3, and 5.
214
215 Screened DH groups may be installed in /etc/moduli. It is important that
216 this file contains moduli of a range of bit lengths and that both ends of
217 a connection share common moduli.
218
219FILES
220 $HOME/.ssh/identity
221 Contains the protocol version 1 RSA authentication identity of
222 the user. This file should not be readable by anyone but the us-
223 er. It is possible to specify a passphrase when generating the
224 key; that passphrase will be used to encrypt the private part of
225 this file using 3DES. This file is not automatically accessed by
226 ssh-keygen but it is offered as the default file for the private
227 key. ssh(1) will read this file when a login attempt is made.
228
229 $HOME/.ssh/identity.pub
230 Contains the protocol version 1 RSA public key for authentica-
231 tion. The contents of this file should be added to
232 $HOME/.ssh/authorized_keys on all machines where the user wishes
233 to log in using RSA authentication. There is no need to keep the
234 contents of this file secret.
235
236 $HOME/.ssh/id_dsa
237 Contains the protocol version 2 DSA authentication identity of
238 the user. This file should not be readable by anyone but the us-
239 er. It is possible to specify a passphrase when generating the
240 key; that passphrase will be used to encrypt the private part of
241 this file using 3DES. This file is not automatically accessed by
242 ssh-keygen but it is offered as the default file for the private
243 key. ssh(1) will read this file when a login attempt is made.
244
245 $HOME/.ssh/id_dsa.pub
246 Contains the protocol version 2 DSA public key for authentica-
247 tion. The contents of this file should be added to
248 $HOME/.ssh/authorized_keys on all machines where the user wishes
249 to log in using public key authentication. There is no need to
250 keep the contents of this file secret.
251
252 $HOME/.ssh/id_rsa
253 Contains the protocol version 2 RSA authentication identity of
254 the user. This file should not be readable by anyone but the us-
255 er. It is possible to specify a passphrase when generating the
256 key; that passphrase will be used to encrypt the private part of
257 this file using 3DES. This file is not automatically accessed by
258 ssh-keygen but it is offered as the default file for the private
259 key. ssh(1) will read this file when a login attempt is made.
260
261 $HOME/.ssh/id_rsa.pub
262 Contains the protocol version 2 RSA public key for authentica-
263 tion. The contents of this file should be added to
264 $HOME/.ssh/authorized_keys on all machines where the user wishes
265 to log in using public key authentication. There is no need to
266 keep the contents of this file secret.
267
268 /etc/moduli
269 Contains Diffie-Hellman groups used for DH-GEX. The file format
270 is described in moduli(5).
271
272SEE ALSO
273 ssh(1), ssh-add(1), ssh-agent(1), moduli(5), sshd(8)
274
275 J. Galbraith and R. Thayer, SECSH Public Key File Format, draft-ietf-
276 secsh-publickeyfile-01.txt, March 2001, work in progress material.
277
278AUTHORS
279 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
280 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
281 de Raadt and Dug Song removed many bugs, re-added newer features and
282 created OpenSSH. Markus Friedl contributed the support for SSH protocol
283 versions 1.5 and 2.0.
284
285OpenBSD 3.7 September 25, 1999 5