Annotation of src/usr.bin/ssh/ssh-keygen.1, Revision 1.79
1.79 ! sthen 1: .\" $OpenBSD: ssh-keygen.1,v 1.78 2008/06/12 19:10:09 jmc 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: .\"
1.79 ! sthen 40: .Dd $Mdocdate: June 12 2008 $
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
82: .Fl D Ar reader
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
93: .Nm ssh-keygen
1.48 jakob 94: .Fl U Ar reader
95: .Op Fl f Ar input_keyfile
1.57 jakob 96: .Nm ssh-keygen
97: .Fl r Ar hostname
98: .Op Fl f Ar input_keyfile
99: .Op Fl g
1.60 djm 100: .Nm ssh-keygen
101: .Fl G Ar output_file
1.61 djm 102: .Op Fl v
1.60 djm 103: .Op Fl b Ar bits
104: .Op Fl M Ar memory
105: .Op Fl S Ar start_point
106: .Nm ssh-keygen
107: .Fl T Ar output_file
108: .Fl f Ar input_file
1.61 djm 109: .Op Fl v
1.60 djm 110: .Op Fl a Ar num_trials
111: .Op Fl W Ar generator
1.13 aaron 112: .Sh DESCRIPTION
1.2 deraadt 113: .Nm
1.37 markus 114: generates, manages and converts authentication keys for
1.2 deraadt 115: .Xr ssh 1 .
1.15 deraadt 116: .Nm
1.54 deraadt 117: can create RSA keys for use by SSH protocol version 1 and RSA or DSA
1.58 jmc 118: keys for use by SSH protocol version 2.
119: The type of key to be generated is specified with the
1.25 markus 120: .Fl t
1.52 djm 121: option.
1.70 djm 122: If invoked without any arguments,
123: .Nm
1.71 jmc 124: will generate an RSA key for use in SSH protocol 2 connections.
1.15 deraadt 125: .Pp
1.60 djm 126: .Nm
127: is also used to generate groups for use in Diffie-Hellman group
128: exchange (DH-GEX).
129: See the
130: .Sx MODULI GENERATION
131: section for details.
132: .Pp
1.2 deraadt 133: Normally each user wishing to use SSH
1.15 deraadt 134: with RSA or DSA authentication runs this once to create the authentication
1.1 deraadt 135: key in
1.68 djm 136: .Pa ~/.ssh/identity ,
137: .Pa ~/.ssh/id_dsa
1.15 deraadt 138: or
1.68 djm 139: .Pa ~/.ssh/id_rsa .
1.15 deraadt 140: Additionally, the system administrator may use this to generate host keys,
141: as seen in
142: .Pa /etc/rc .
1.2 deraadt 143: .Pp
1.1 deraadt 144: Normally this program generates the key and asks for a file in which
1.12 aaron 145: to store the private key.
146: The public key is stored in a file with the same name but
1.2 deraadt 147: .Dq .pub
1.12 aaron 148: appended.
149: The program also asks for a passphrase.
150: The passphrase may be empty to indicate no passphrase
1.26 markus 151: (host keys must have an empty passphrase), or it may be a string of
1.12 aaron 152: arbitrary length.
1.51 stevesk 153: A passphrase is similar to a password, except it can be a phrase with a
154: series of words, punctuation, numbers, whitespace, or any string of
155: characters you want.
156: Good passphrases are 10-30 characters long, are
1.1 deraadt 157: not simple sentences or otherwise easily guessable (English
1.42 markus 158: prose has only 1-2 bits of entropy per character, and provides very bad
1.51 stevesk 159: passphrases), and contain a mix of upper and lowercase letters,
160: numbers, and non-alphanumeric characters.
1.12 aaron 161: The passphrase can be changed later by using the
1.2 deraadt 162: .Fl p
1.1 deraadt 163: option.
1.2 deraadt 164: .Pp
1.12 aaron 165: There is no way to recover a lost passphrase.
166: If the passphrase is
1.49 deraadt 167: lost or forgotten, a new key must be generated and copied to the
1.1 deraadt 168: corresponding public key to other machines.
1.2 deraadt 169: .Pp
1.37 markus 170: For RSA1 keys,
171: there is also a comment field in the key file that is only for
1.12 aaron 172: convenience to the user to help identify the key.
173: The comment can tell what the key is for, or whatever is useful.
174: The comment is initialized to
1.2 deraadt 175: .Dq user@host
176: when the key is created, but can be changed using the
177: .Fl c
1.1 deraadt 178: option.
1.2 deraadt 179: .Pp
1.15 deraadt 180: After a key is generated, instructions below detail where the keys
181: should be placed to be activated.
182: .Pp
1.2 deraadt 183: The options are as follows:
184: .Bl -tag -width Ds
1.60 djm 185: .It Fl a Ar trials
186: Specifies the number of primality tests to perform when screening DH-GEX
187: candidates using the
188: .Fl T
189: command.
1.66 jmc 190: .It Fl B
191: Show the bubblebabble digest of specified private or public key file.
1.2 deraadt 192: .It Fl b Ar bits
1.12 aaron 193: Specifies the number of bits in the key to create.
1.72 dtucker 194: For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
1.69 djm 195: Generally, 2048 bits is considered sufficient.
1.72 dtucker 196: DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
1.66 jmc 197: .It Fl C Ar comment
198: Provides a new comment.
1.2 deraadt 199: .It Fl c
1.1 deraadt 200: Requests changing the comment in the private and public key files.
1.50 markus 201: This operation is only supported for RSA1 keys.
1.1 deraadt 202: The program will prompt for the file containing the private keys, for
1.41 stevesk 203: the passphrase if the key has one, and for the new comment.
1.66 jmc 204: .It Fl D Ar reader
205: Download the RSA public key stored in the smartcard in
206: .Ar reader .
1.37 markus 207: .It Fl e
1.40 markus 208: This option will read a private or public OpenSSH key file and
1.73 markus 209: print the key in
210: RFC 4716 SSH Public Key File Format
1.37 markus 211: to stdout.
212: This option allows exporting keys for use by several commercial
213: SSH implementations.
1.66 jmc 214: .It Fl F Ar hostname
215: Search for the specified
216: .Ar hostname
217: in a
218: .Pa known_hosts
219: file, listing any occurrences found.
220: This option is useful to find hashed host names or addresses and may also be
221: used in conjunction with the
222: .Fl H
223: option to print found keys in a hashed format.
224: .It Fl f Ar filename
225: Specifies the filename of the key file.
226: .It Fl G Ar output_file
227: Generate candidate primes for DH-GEX.
228: These primes must be screened for
229: safety (using the
230: .Fl T
231: option) before use.
1.57 jakob 232: .It Fl g
1.62 jakob 233: Use generic DNS format when printing fingerprint resource records using the
1.63 jmc 234: .Fl r
1.62 jakob 235: command.
1.66 jmc 236: .It Fl H
237: Hash a
238: .Pa known_hosts
1.67 dtucker 239: file.
240: This replaces all hostnames and addresses with hashed representations
241: within the specified file; the original content is moved to a file with
242: a .old suffix.
1.66 jmc 243: These hashes may be used normally by
244: .Nm ssh
245: and
246: .Nm sshd ,
247: but they do not reveal identifying information should the file's contents
248: be disclosed.
249: This option will not modify existing hashed hostnames and is therefore safe
250: to use on files that mix hashed and non-hashed names.
1.37 markus 251: .It Fl i
252: This option will read an unencrypted private (or public) key file
253: in SSH2-compatible format and print an OpenSSH compatible private
254: (or public) key to stdout.
255: .Nm
1.38 markus 256: also reads the
1.74 jmc 257: RFC 4716 SSH Public Key File Format.
1.37 markus 258: This option allows importing keys from several commercial
259: SSH implementations.
1.9 markus 260: .It Fl l
1.77 grunk 261: Show fingerprint of specified public key file.
1.50 markus 262: Private RSA1 keys are also supported.
263: For RSA and DSA keys
264: .Nm
1.78 jmc 265: tries to find the matching public key file and prints its fingerprint.
266: If combined with
267: .Fl v ,
268: an ASCII art representation of the key is supplied with the fingerprint.
1.66 jmc 269: .It Fl M Ar memory
270: Specify the amount of memory to use (in megabytes) when generating
271: candidate moduli for DH-GEX.
272: .It Fl N Ar new_passphrase
273: Provides the new passphrase.
274: .It Fl P Ar passphrase
275: Provides the (old) passphrase.
1.2 deraadt 276: .It Fl p
1.1 deraadt 277: Requests changing the passphrase of a private key file instead of
1.12 aaron 278: creating a new private key.
279: The program will prompt for the file
1.1 deraadt 280: containing the private key, for the old passphrase, and twice for the
281: new passphrase.
1.5 aaron 282: .It Fl q
283: Silence
284: .Nm ssh-keygen .
285: Used by
286: .Pa /etc/rc
287: when creating a new key.
1.64 djm 288: .It Fl R Ar hostname
289: Removes all keys belonging to
290: .Ar hostname
1.65 jmc 291: from a
1.64 djm 292: .Pa known_hosts
293: file.
1.65 jmc 294: This option is useful to delete hashed hosts (see the
1.64 djm 295: .Fl H
296: option above).
1.66 jmc 297: .It Fl r Ar hostname
298: Print the SSHFP fingerprint resource record named
299: .Ar hostname
300: for the specified public key file.
1.60 djm 301: .It Fl S Ar start
302: Specify start point (in hex) when generating candidate moduli for DH-GEX.
303: .It Fl T Ar output_file
304: Test DH group exchange candidate primes (generated using the
305: .Fl G
306: option) for safety.
1.66 jmc 307: .It Fl t Ar type
308: Specifies the type of key to create.
309: The possible values are
310: .Dq rsa1
311: for protocol version 1 and
312: .Dq rsa
313: or
314: .Dq dsa
315: for protocol version 2.
1.48 jakob 316: .It Fl U Ar reader
317: Upload an existing RSA private key into the smartcard in
318: .Ar reader .
1.61 djm 319: .It Fl v
320: Verbose mode.
321: Causes
322: .Nm
323: to print debugging messages about its progress.
324: This is helpful for debugging moduli generation.
325: Multiple
326: .Fl v
327: options increase the verbosity.
328: The maximum is 3.
1.66 jmc 329: .It Fl W Ar generator
330: Specify desired generator when testing candidate moduli for DH-GEX.
331: .It Fl y
332: This option will read a private
333: OpenSSH format file and print an OpenSSH public key to stdout.
1.2 deraadt 334: .El
1.60 djm 335: .Sh MODULI GENERATION
336: .Nm
337: may be used to generate groups for the Diffie-Hellman Group Exchange
338: (DH-GEX) protocol.
339: Generating these groups is a two-step process: first, candidate
340: primes are generated using a fast, but memory intensive process.
341: These candidate primes are then tested for suitability (a CPU-intensive
342: process).
343: .Pp
344: Generation of primes is performed using the
345: .Fl G
346: option.
347: The desired length of the primes may be specified by the
348: .Fl b
349: option.
350: For example:
351: .Pp
1.66 jmc 352: .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
1.60 djm 353: .Pp
354: By default, the search for primes begins at a random point in the
355: desired length range.
356: This may be overridden using the
357: .Fl S
358: option, which specifies a different start point (in hex).
359: .Pp
360: Once a set of candidates have been generated, they must be tested for
361: suitability.
362: This may be performed using the
363: .Fl T
364: option.
365: In this mode
366: .Nm
367: will read candidates from standard input (or a file specified using the
368: .Fl f
369: option).
370: For example:
371: .Pp
1.66 jmc 372: .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
1.60 djm 373: .Pp
374: By default, each candidate will be subjected to 100 primality tests.
375: This may be overridden using the
376: .Fl a
377: option.
378: The DH generator value will be chosen automatically for the
379: prime under consideration.
380: If a specific generator is desired, it may be requested using the
381: .Fl W
382: option.
1.66 jmc 383: Valid generator values are 2, 3, and 5.
1.60 djm 384: .Pp
385: Screened DH groups may be installed in
386: .Pa /etc/moduli .
387: It is important that this file contains moduli of a range of bit lengths and
388: that both ends of a connection share common moduli.
1.2 deraadt 389: .Sh FILES
390: .Bl -tag -width Ds
1.68 djm 391: .It Pa ~/.ssh/identity
1.36 itojun 392: Contains the protocol version 1 RSA authentication identity of the user.
1.12 aaron 393: This file should not be readable by anyone but the user.
394: It is possible to
1.1 deraadt 395: specify a passphrase when generating the key; that passphrase will be
1.12 aaron 396: used to encrypt the private part of this file using 3DES.
397: This file is not automatically accessed by
1.2 deraadt 398: .Nm
1.1 deraadt 399: but it is offered as the default file for the private key.
1.46 markus 400: .Xr ssh 1
1.15 deraadt 401: will read this file when a login attempt is made.
1.68 djm 402: .It Pa ~/.ssh/identity.pub
1.36 itojun 403: Contains the protocol version 1 RSA public key for authentication.
1.12 aaron 404: The contents of this file should be added to
1.68 djm 405: .Pa ~/.ssh/authorized_keys
1.2 deraadt 406: on all machines
1.49 deraadt 407: where the user wishes to log in using RSA authentication.
1.15 deraadt 408: There is no need to keep the contents of this file secret.
1.68 djm 409: .It Pa ~/.ssh/id_dsa
1.36 itojun 410: Contains the protocol version 2 DSA authentication identity of the user.
1.15 deraadt 411: This file should not be readable by anyone but the user.
412: It is possible to
413: specify a passphrase when generating the key; that passphrase will be
414: used to encrypt the private part of this file using 3DES.
415: This file is not automatically accessed by
416: .Nm
417: but it is offered as the default file for the private key.
1.46 markus 418: .Xr ssh 1
1.15 deraadt 419: will read this file when a login attempt is made.
1.68 djm 420: .It Pa ~/.ssh/id_dsa.pub
1.36 itojun 421: Contains the protocol version 2 DSA public key for authentication.
422: The contents of this file should be added to
1.68 djm 423: .Pa ~/.ssh/authorized_keys
1.36 itojun 424: on all machines
1.49 deraadt 425: where the user wishes to log in using public key authentication.
1.36 itojun 426: There is no need to keep the contents of this file secret.
1.68 djm 427: .It Pa ~/.ssh/id_rsa
1.36 itojun 428: Contains the protocol version 2 RSA authentication identity of the user.
429: This file should not be readable by anyone but the user.
430: It is possible to
431: specify a passphrase when generating the key; that passphrase will be
432: used to encrypt the private part of this file using 3DES.
433: This file is not automatically accessed by
434: .Nm
435: but it is offered as the default file for the private key.
1.46 markus 436: .Xr ssh 1
1.36 itojun 437: will read this file when a login attempt is made.
1.68 djm 438: .It Pa ~/.ssh/id_rsa.pub
1.36 itojun 439: Contains the protocol version 2 RSA public key for authentication.
1.15 deraadt 440: The contents of this file should be added to
1.68 djm 441: .Pa ~/.ssh/authorized_keys
1.15 deraadt 442: on all machines
1.49 deraadt 443: where the user wishes to log in using public key authentication.
1.12 aaron 444: There is no need to keep the contents of this file secret.
1.60 djm 445: .It Pa /etc/moduli
446: Contains Diffie-Hellman groups used for DH-GEX.
447: The file format is described in
448: .Xr moduli 5 .
1.19 aaron 449: .El
1.2 deraadt 450: .Sh SEE ALSO
451: .Xr ssh 1 ,
452: .Xr ssh-add 1 ,
1.8 ericj 453: .Xr ssh-agent 1 ,
1.60 djm 454: .Xr moduli 5 ,
1.30 itojun 455: .Xr sshd 8
1.37 markus 456: .Rs
1.73 markus 457: .%R RFC 4716
458: .%T "The Secure Shell (SSH) Public Key File Format"
459: .%D 2006
1.37 markus 460: .Re
1.59 jmc 461: .Sh AUTHORS
462: OpenSSH is a derivative of the original and free
463: ssh 1.2.12 release by Tatu Ylonen.
464: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
465: Theo de Raadt and Dug Song
466: removed many bugs, re-added newer features and
467: created OpenSSH.
468: Markus Friedl contributed the support for SSH
469: protocol versions 1.5 and 2.0.
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