Annotation of src/usr.bin/ssh/ssh-keygen.1, Revision 1.82
1.82 ! jmc 1: .\" $OpenBSD: ssh-keygen.1,v 1.81 2010/02/08 10:50:20 markus Exp $
1.29 niklas 2: .\"
1.1 deraadt 3: .\" -*- nroff -*-
4: .\"
5: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
6: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
7: .\" All rights reserved
8: .\"
1.22 deraadt 9: .\" As far as I am concerned, the code I have written for this software
10: .\" can be used freely for any purpose. Any derived versions of this
11: .\" software must be clearly marked as such, and if the derived work is
12: .\" incompatible with the protocol description in the RFC file, it must be
13: .\" called by a name other than "ssh" or "Secure Shell".
14: .\"
15: .\"
1.33 deraadt 16: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
17: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
18: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
1.22 deraadt 19: .\"
20: .\" Redistribution and use in source and binary forms, with or without
21: .\" modification, are permitted provided that the following conditions
22: .\" are met:
23: .\" 1. Redistributions of source code must retain the above copyright
24: .\" notice, this list of conditions and the following disclaimer.
25: .\" 2. Redistributions in binary form must reproduce the above copyright
26: .\" notice, this list of conditions and the following disclaimer in the
27: .\" documentation and/or other materials provided with the distribution.
1.1 deraadt 28: .\"
1.22 deraadt 29: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
30: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
31: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
32: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
33: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
34: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
35: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
36: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
37: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
38: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.1 deraadt 39: .\"
1.82 ! jmc 40: .Dd $Mdocdate: February 8 2010 $
1.2 deraadt 41: .Dt SSH-KEYGEN 1
42: .Os
43: .Sh NAME
44: .Nm ssh-keygen
1.37 markus 45: .Nd authentication key generation, management and conversion
1.2 deraadt 46: .Sh SYNOPSIS
47: .Nm ssh-keygen
1.56 jmc 48: .Bk -words
1.25 markus 49: .Op Fl q
1.2 deraadt 50: .Op Fl b Ar bits
1.53 stevesk 51: .Fl t Ar type
1.2 deraadt 52: .Op Fl N Ar new_passphrase
53: .Op Fl C Ar comment
1.20 markus 54: .Op Fl f Ar output_keyfile
1.56 jmc 55: .Ek
1.2 deraadt 56: .Nm ssh-keygen
57: .Fl p
58: .Op Fl P Ar old_passphrase
59: .Op Fl N Ar new_passphrase
1.9 markus 60: .Op Fl f Ar keyfile
1.2 deraadt 61: .Nm ssh-keygen
1.37 markus 62: .Fl i
1.20 markus 63: .Op Fl f Ar input_keyfile
1.16 deraadt 64: .Nm ssh-keygen
1.37 markus 65: .Fl e
1.20 markus 66: .Op Fl f Ar input_keyfile
1.16 deraadt 67: .Nm ssh-keygen
1.17 markus 68: .Fl y
1.20 markus 69: .Op Fl f Ar input_keyfile
1.17 markus 70: .Nm ssh-keygen
1.2 deraadt 71: .Fl c
72: .Op Fl P Ar passphrase
73: .Op Fl C Ar comment
1.9 markus 74: .Op Fl f Ar keyfile
75: .Nm ssh-keygen
76: .Fl l
1.35 markus 77: .Op Fl f Ar input_keyfile
78: .Nm ssh-keygen
79: .Fl B
1.20 markus 80: .Op Fl f Ar input_keyfile
1.48 jakob 81: .Nm ssh-keygen
1.82 ! jmc 82: .Fl D Ar pkcs11
1.48 jakob 83: .Nm ssh-keygen
1.64 djm 84: .Fl F Ar hostname
85: .Op Fl f Ar known_hosts_file
1.79 sthen 86: .Op Fl l
1.64 djm 87: .Nm ssh-keygen
88: .Fl H
89: .Op Fl f Ar known_hosts_file
90: .Nm ssh-keygen
91: .Fl R Ar hostname
92: .Op Fl f Ar known_hosts_file
1.57 jakob 93: .Nm ssh-keygen
94: .Fl r Ar hostname
95: .Op Fl f Ar input_keyfile
96: .Op Fl g
1.60 djm 97: .Nm ssh-keygen
98: .Fl G Ar output_file
1.61 djm 99: .Op Fl v
1.60 djm 100: .Op Fl b Ar bits
101: .Op Fl M Ar memory
102: .Op Fl S Ar start_point
103: .Nm ssh-keygen
104: .Fl T Ar output_file
105: .Fl f Ar input_file
1.61 djm 106: .Op Fl v
1.60 djm 107: .Op Fl a Ar num_trials
108: .Op Fl W Ar generator
1.13 aaron 109: .Sh DESCRIPTION
1.2 deraadt 110: .Nm
1.37 markus 111: generates, manages and converts authentication keys for
1.2 deraadt 112: .Xr ssh 1 .
1.15 deraadt 113: .Nm
1.54 deraadt 114: can create RSA keys for use by SSH protocol version 1 and RSA or DSA
1.58 jmc 115: keys for use by SSH protocol version 2.
116: The type of key to be generated is specified with the
1.25 markus 117: .Fl t
1.52 djm 118: option.
1.70 djm 119: If invoked without any arguments,
120: .Nm
1.71 jmc 121: will generate an RSA key for use in SSH protocol 2 connections.
1.15 deraadt 122: .Pp
1.60 djm 123: .Nm
124: is also used to generate groups for use in Diffie-Hellman group
125: exchange (DH-GEX).
126: See the
127: .Sx MODULI GENERATION
128: section for details.
129: .Pp
1.2 deraadt 130: Normally each user wishing to use SSH
1.15 deraadt 131: with RSA or DSA authentication runs this once to create the authentication
1.1 deraadt 132: key in
1.68 djm 133: .Pa ~/.ssh/identity ,
134: .Pa ~/.ssh/id_dsa
1.15 deraadt 135: or
1.68 djm 136: .Pa ~/.ssh/id_rsa .
1.15 deraadt 137: Additionally, the system administrator may use this to generate host keys,
138: as seen in
139: .Pa /etc/rc .
1.2 deraadt 140: .Pp
1.1 deraadt 141: Normally this program generates the key and asks for a file in which
1.12 aaron 142: to store the private key.
143: The public key is stored in a file with the same name but
1.2 deraadt 144: .Dq .pub
1.12 aaron 145: appended.
146: The program also asks for a passphrase.
147: The passphrase may be empty to indicate no passphrase
1.26 markus 148: (host keys must have an empty passphrase), or it may be a string of
1.12 aaron 149: arbitrary length.
1.51 stevesk 150: A passphrase is similar to a password, except it can be a phrase with a
151: series of words, punctuation, numbers, whitespace, or any string of
152: characters you want.
153: Good passphrases are 10-30 characters long, are
1.1 deraadt 154: not simple sentences or otherwise easily guessable (English
1.42 markus 155: prose has only 1-2 bits of entropy per character, and provides very bad
1.51 stevesk 156: passphrases), and contain a mix of upper and lowercase letters,
157: numbers, and non-alphanumeric characters.
1.12 aaron 158: The passphrase can be changed later by using the
1.2 deraadt 159: .Fl p
1.1 deraadt 160: option.
1.2 deraadt 161: .Pp
1.12 aaron 162: There is no way to recover a lost passphrase.
163: If the passphrase is
1.49 deraadt 164: lost or forgotten, a new key must be generated and copied to the
1.1 deraadt 165: corresponding public key to other machines.
1.2 deraadt 166: .Pp
1.37 markus 167: For RSA1 keys,
168: there is also a comment field in the key file that is only for
1.12 aaron 169: convenience to the user to help identify the key.
170: The comment can tell what the key is for, or whatever is useful.
171: The comment is initialized to
1.2 deraadt 172: .Dq user@host
173: when the key is created, but can be changed using the
174: .Fl c
1.1 deraadt 175: option.
1.2 deraadt 176: .Pp
1.15 deraadt 177: After a key is generated, instructions below detail where the keys
178: should be placed to be activated.
179: .Pp
1.2 deraadt 180: The options are as follows:
181: .Bl -tag -width Ds
1.60 djm 182: .It Fl a Ar trials
183: Specifies the number of primality tests to perform when screening DH-GEX
184: candidates using the
185: .Fl T
186: command.
1.66 jmc 187: .It Fl B
188: Show the bubblebabble digest of specified private or public key file.
1.2 deraadt 189: .It Fl b Ar bits
1.12 aaron 190: Specifies the number of bits in the key to create.
1.72 dtucker 191: For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
1.69 djm 192: Generally, 2048 bits is considered sufficient.
1.72 dtucker 193: DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
1.66 jmc 194: .It Fl C Ar comment
195: Provides a new comment.
1.2 deraadt 196: .It Fl c
1.1 deraadt 197: Requests changing the comment in the private and public key files.
1.50 markus 198: This operation is only supported for RSA1 keys.
1.1 deraadt 199: The program will prompt for the file containing the private keys, for
1.41 stevesk 200: the passphrase if the key has one, and for the new comment.
1.81 markus 201: .It Fl D Ar pkcs11
202: Download the RSA public keys stored in the
203: .Ar pkcs11
204: provider.
1.37 markus 205: .It Fl e
1.40 markus 206: This option will read a private or public OpenSSH key file and
1.73 markus 207: print the key in
208: RFC 4716 SSH Public Key File Format
1.37 markus 209: to stdout.
210: This option allows exporting keys for use by several commercial
211: SSH implementations.
1.66 jmc 212: .It Fl F Ar hostname
213: Search for the specified
214: .Ar hostname
215: in a
216: .Pa known_hosts
217: file, listing any occurrences found.
218: This option is useful to find hashed host names or addresses and may also be
219: used in conjunction with the
220: .Fl H
221: option to print found keys in a hashed format.
222: .It Fl f Ar filename
223: Specifies the filename of the key file.
224: .It Fl G Ar output_file
225: Generate candidate primes for DH-GEX.
226: These primes must be screened for
227: safety (using the
228: .Fl T
229: option) before use.
1.57 jakob 230: .It Fl g
1.62 jakob 231: Use generic DNS format when printing fingerprint resource records using the
1.63 jmc 232: .Fl r
1.62 jakob 233: command.
1.66 jmc 234: .It Fl H
235: Hash a
236: .Pa known_hosts
1.67 dtucker 237: file.
238: This replaces all hostnames and addresses with hashed representations
239: within the specified file; the original content is moved to a file with
240: a .old suffix.
1.66 jmc 241: These hashes may be used normally by
242: .Nm ssh
243: and
244: .Nm sshd ,
245: but they do not reveal identifying information should the file's contents
246: be disclosed.
247: This option will not modify existing hashed hostnames and is therefore safe
248: to use on files that mix hashed and non-hashed names.
1.37 markus 249: .It Fl i
250: This option will read an unencrypted private (or public) key file
251: in SSH2-compatible format and print an OpenSSH compatible private
252: (or public) key to stdout.
253: .Nm
1.38 markus 254: also reads the
1.74 jmc 255: RFC 4716 SSH Public Key File Format.
1.37 markus 256: This option allows importing keys from several commercial
257: SSH implementations.
1.9 markus 258: .It Fl l
1.77 grunk 259: Show fingerprint of specified public key file.
1.50 markus 260: Private RSA1 keys are also supported.
261: For RSA and DSA keys
262: .Nm
1.78 jmc 263: tries to find the matching public key file and prints its fingerprint.
264: If combined with
265: .Fl v ,
266: an ASCII art representation of the key is supplied with the fingerprint.
1.66 jmc 267: .It Fl M Ar memory
268: Specify the amount of memory to use (in megabytes) when generating
269: candidate moduli for DH-GEX.
270: .It Fl N Ar new_passphrase
271: Provides the new passphrase.
272: .It Fl P Ar passphrase
273: Provides the (old) passphrase.
1.2 deraadt 274: .It Fl p
1.1 deraadt 275: Requests changing the passphrase of a private key file instead of
1.12 aaron 276: creating a new private key.
277: The program will prompt for the file
1.1 deraadt 278: containing the private key, for the old passphrase, and twice for the
279: new passphrase.
1.5 aaron 280: .It Fl q
281: Silence
282: .Nm ssh-keygen .
283: Used by
284: .Pa /etc/rc
285: when creating a new key.
1.64 djm 286: .It Fl R Ar hostname
287: Removes all keys belonging to
288: .Ar hostname
1.65 jmc 289: from a
1.64 djm 290: .Pa known_hosts
291: file.
1.65 jmc 292: This option is useful to delete hashed hosts (see the
1.64 djm 293: .Fl H
294: option above).
1.66 jmc 295: .It Fl r Ar hostname
296: Print the SSHFP fingerprint resource record named
297: .Ar hostname
298: for the specified public key file.
1.60 djm 299: .It Fl S Ar start
300: Specify start point (in hex) when generating candidate moduli for DH-GEX.
301: .It Fl T Ar output_file
302: Test DH group exchange candidate primes (generated using the
303: .Fl G
304: option) for safety.
1.66 jmc 305: .It Fl t Ar type
306: Specifies the type of key to create.
307: The possible values are
308: .Dq rsa1
309: for protocol version 1 and
310: .Dq rsa
311: or
312: .Dq dsa
313: for protocol version 2.
1.61 djm 314: .It Fl v
315: Verbose mode.
316: Causes
317: .Nm
318: to print debugging messages about its progress.
319: This is helpful for debugging moduli generation.
320: Multiple
321: .Fl v
322: options increase the verbosity.
323: The maximum is 3.
1.66 jmc 324: .It Fl W Ar generator
325: Specify desired generator when testing candidate moduli for DH-GEX.
326: .It Fl y
327: This option will read a private
328: OpenSSH format file and print an OpenSSH public key to stdout.
1.2 deraadt 329: .El
1.60 djm 330: .Sh MODULI GENERATION
331: .Nm
332: may be used to generate groups for the Diffie-Hellman Group Exchange
333: (DH-GEX) protocol.
334: Generating these groups is a two-step process: first, candidate
335: primes are generated using a fast, but memory intensive process.
336: These candidate primes are then tested for suitability (a CPU-intensive
337: process).
338: .Pp
339: Generation of primes is performed using the
340: .Fl G
341: option.
342: The desired length of the primes may be specified by the
343: .Fl b
344: option.
345: For example:
346: .Pp
1.66 jmc 347: .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
1.60 djm 348: .Pp
349: By default, the search for primes begins at a random point in the
350: desired length range.
351: This may be overridden using the
352: .Fl S
353: option, which specifies a different start point (in hex).
354: .Pp
355: Once a set of candidates have been generated, they must be tested for
356: suitability.
357: This may be performed using the
358: .Fl T
359: option.
360: In this mode
361: .Nm
362: will read candidates from standard input (or a file specified using the
363: .Fl f
364: option).
365: For example:
366: .Pp
1.66 jmc 367: .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
1.60 djm 368: .Pp
369: By default, each candidate will be subjected to 100 primality tests.
370: This may be overridden using the
371: .Fl a
372: option.
373: The DH generator value will be chosen automatically for the
374: prime under consideration.
375: If a specific generator is desired, it may be requested using the
376: .Fl W
377: option.
1.66 jmc 378: Valid generator values are 2, 3, and 5.
1.60 djm 379: .Pp
380: Screened DH groups may be installed in
381: .Pa /etc/moduli .
382: It is important that this file contains moduli of a range of bit lengths and
383: that both ends of a connection share common moduli.
1.2 deraadt 384: .Sh FILES
385: .Bl -tag -width Ds
1.68 djm 386: .It Pa ~/.ssh/identity
1.36 itojun 387: Contains the protocol version 1 RSA authentication identity of the user.
1.12 aaron 388: This file should not be readable by anyone but the user.
389: It is possible to
1.1 deraadt 390: specify a passphrase when generating the key; that passphrase will be
1.80 dtucker 391: used to encrypt the private part of this file using 128-bit AES.
1.12 aaron 392: This file is not automatically accessed by
1.2 deraadt 393: .Nm
1.1 deraadt 394: but it is offered as the default file for the private key.
1.46 markus 395: .Xr ssh 1
1.15 deraadt 396: will read this file when a login attempt is made.
1.68 djm 397: .It Pa ~/.ssh/identity.pub
1.36 itojun 398: Contains the protocol version 1 RSA public key for authentication.
1.12 aaron 399: The contents of this file should be added to
1.68 djm 400: .Pa ~/.ssh/authorized_keys
1.2 deraadt 401: on all machines
1.49 deraadt 402: where the user wishes to log in using RSA authentication.
1.15 deraadt 403: There is no need to keep the contents of this file secret.
1.68 djm 404: .It Pa ~/.ssh/id_dsa
1.36 itojun 405: Contains the protocol version 2 DSA authentication identity of the user.
1.15 deraadt 406: This file should not be readable by anyone but the user.
407: It is possible to
408: specify a passphrase when generating the key; that passphrase will be
1.80 dtucker 409: used to encrypt the private part of this file using 128-bit AES.
1.15 deraadt 410: This file is not automatically accessed by
411: .Nm
412: but it is offered as the default file for the private key.
1.46 markus 413: .Xr ssh 1
1.15 deraadt 414: will read this file when a login attempt is made.
1.68 djm 415: .It Pa ~/.ssh/id_dsa.pub
1.36 itojun 416: Contains the protocol version 2 DSA public key for authentication.
417: The contents of this file should be added to
1.68 djm 418: .Pa ~/.ssh/authorized_keys
1.36 itojun 419: on all machines
1.49 deraadt 420: where the user wishes to log in using public key authentication.
1.36 itojun 421: There is no need to keep the contents of this file secret.
1.68 djm 422: .It Pa ~/.ssh/id_rsa
1.36 itojun 423: Contains the protocol version 2 RSA authentication identity of the user.
424: This file should not be readable by anyone but the user.
425: It is possible to
426: specify a passphrase when generating the key; that passphrase will be
1.80 dtucker 427: used to encrypt the private part of this file using 128-bit AES.
1.36 itojun 428: This file is not automatically accessed by
429: .Nm
430: but it is offered as the default file for the private key.
1.46 markus 431: .Xr ssh 1
1.36 itojun 432: will read this file when a login attempt is made.
1.68 djm 433: .It Pa ~/.ssh/id_rsa.pub
1.36 itojun 434: Contains the protocol version 2 RSA public key for authentication.
1.15 deraadt 435: The contents of this file should be added to
1.68 djm 436: .Pa ~/.ssh/authorized_keys
1.15 deraadt 437: on all machines
1.49 deraadt 438: where the user wishes to log in using public key authentication.
1.12 aaron 439: There is no need to keep the contents of this file secret.
1.60 djm 440: .It Pa /etc/moduli
441: Contains Diffie-Hellman groups used for DH-GEX.
442: The file format is described in
443: .Xr moduli 5 .
1.19 aaron 444: .El
1.2 deraadt 445: .Sh SEE ALSO
446: .Xr ssh 1 ,
447: .Xr ssh-add 1 ,
1.8 ericj 448: .Xr ssh-agent 1 ,
1.60 djm 449: .Xr moduli 5 ,
1.30 itojun 450: .Xr sshd 8
1.37 markus 451: .Rs
1.73 markus 452: .%R RFC 4716
453: .%T "The Secure Shell (SSH) Public Key File Format"
454: .%D 2006
1.37 markus 455: .Re
1.59 jmc 456: .Sh AUTHORS
457: OpenSSH is a derivative of the original and free
458: ssh 1.2.12 release by Tatu Ylonen.
459: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
460: Theo de Raadt and Dug Song
461: removed many bugs, re-added newer features and
462: created OpenSSH.
463: Markus Friedl contributed the support for SSH
464: protocol versions 1.5 and 2.0.