Annotation of src/usr.bin/ssh/ssh-keygen.1, Revision 1.76
1.76 ! grunk 1: .\" $OpenBSD: ssh-keygen.1,v 1.75 2007/05/31 19:20:16 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: .\"
1.76 ! grunk 40: .Dd $Mdocdate: May 31 2007 $
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
86: .Nm ssh-keygen
87: .Fl H
88: .Op Fl f Ar known_hosts_file
89: .Nm ssh-keygen
90: .Fl R Ar hostname
91: .Op Fl f Ar known_hosts_file
92: .Nm ssh-keygen
1.48 jakob 93: .Fl U Ar reader
94: .Op Fl f Ar input_keyfile
1.57 jakob 95: .Nm ssh-keygen
96: .Fl r Ar hostname
97: .Op Fl f Ar input_keyfile
98: .Op Fl g
1.60 djm 99: .Nm ssh-keygen
100: .Fl G Ar output_file
1.61 djm 101: .Op Fl v
1.60 djm 102: .Op Fl b Ar bits
103: .Op Fl M Ar memory
104: .Op Fl S Ar start_point
105: .Nm ssh-keygen
106: .Fl T Ar output_file
107: .Fl f Ar input_file
1.61 djm 108: .Op Fl v
1.60 djm 109: .Op Fl a Ar num_trials
110: .Op Fl W Ar generator
1.13 aaron 111: .Sh DESCRIPTION
1.2 deraadt 112: .Nm
1.37 markus 113: generates, manages and converts authentication keys for
1.2 deraadt 114: .Xr ssh 1 .
1.15 deraadt 115: .Nm
1.54 deraadt 116: can create RSA keys for use by SSH protocol version 1 and RSA or DSA
1.58 jmc 117: keys for use by SSH protocol version 2.
118: The type of key to be generated is specified with the
1.25 markus 119: .Fl t
1.52 djm 120: option.
1.70 djm 121: If invoked without any arguments,
122: .Nm
1.71 jmc 123: will generate an RSA key for use in SSH protocol 2 connections.
1.15 deraadt 124: .Pp
1.60 djm 125: .Nm
126: is also used to generate groups for use in Diffie-Hellman group
127: exchange (DH-GEX).
128: See the
129: .Sx MODULI GENERATION
130: section for details.
131: .Pp
1.2 deraadt 132: Normally each user wishing to use SSH
1.15 deraadt 133: with RSA or DSA authentication runs this once to create the authentication
1.1 deraadt 134: key in
1.68 djm 135: .Pa ~/.ssh/identity ,
136: .Pa ~/.ssh/id_dsa
1.15 deraadt 137: or
1.68 djm 138: .Pa ~/.ssh/id_rsa .
1.15 deraadt 139: Additionally, the system administrator may use this to generate host keys,
140: as seen in
141: .Pa /etc/rc .
1.2 deraadt 142: .Pp
1.1 deraadt 143: Normally this program generates the key and asks for a file in which
1.12 aaron 144: to store the private key.
145: The public key is stored in a file with the same name but
1.2 deraadt 146: .Dq .pub
1.12 aaron 147: appended.
148: The program also asks for a passphrase.
149: The passphrase may be empty to indicate no passphrase
1.26 markus 150: (host keys must have an empty passphrase), or it may be a string of
1.12 aaron 151: arbitrary length.
1.51 stevesk 152: A passphrase is similar to a password, except it can be a phrase with a
153: series of words, punctuation, numbers, whitespace, or any string of
154: characters you want.
155: Good passphrases are 10-30 characters long, are
1.1 deraadt 156: not simple sentences or otherwise easily guessable (English
1.42 markus 157: prose has only 1-2 bits of entropy per character, and provides very bad
1.51 stevesk 158: passphrases), and contain a mix of upper and lowercase letters,
159: numbers, and non-alphanumeric characters.
1.12 aaron 160: The passphrase can be changed later by using the
1.2 deraadt 161: .Fl p
1.1 deraadt 162: option.
1.2 deraadt 163: .Pp
1.12 aaron 164: There is no way to recover a lost passphrase.
165: If the passphrase is
1.49 deraadt 166: lost or forgotten, a new key must be generated and copied to the
1.1 deraadt 167: corresponding public key to other machines.
1.2 deraadt 168: .Pp
1.37 markus 169: For RSA1 keys,
170: there is also a comment field in the key file that is only for
1.12 aaron 171: convenience to the user to help identify the key.
172: The comment can tell what the key is for, or whatever is useful.
173: The comment is initialized to
1.2 deraadt 174: .Dq user@host
175: when the key is created, but can be changed using the
176: .Fl c
1.1 deraadt 177: option.
1.2 deraadt 178: .Pp
1.15 deraadt 179: After a key is generated, instructions below detail where the keys
180: should be placed to be activated.
181: .Pp
1.2 deraadt 182: The options are as follows:
183: .Bl -tag -width Ds
1.60 djm 184: .It Fl a Ar trials
185: Specifies the number of primality tests to perform when screening DH-GEX
186: candidates using the
187: .Fl T
188: command.
1.66 jmc 189: .It Fl B
190: Show the bubblebabble digest of specified private or public key file.
1.2 deraadt 191: .It Fl b Ar bits
1.12 aaron 192: Specifies the number of bits in the key to create.
1.72 dtucker 193: For RSA keys, the minimum size is 768 bits and the default is 2048 bits.
1.69 djm 194: Generally, 2048 bits is considered sufficient.
1.72 dtucker 195: DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
1.66 jmc 196: .It Fl C Ar comment
197: Provides a new comment.
1.2 deraadt 198: .It Fl c
1.1 deraadt 199: Requests changing the comment in the private and public key files.
1.50 markus 200: This operation is only supported for RSA1 keys.
1.1 deraadt 201: The program will prompt for the file containing the private keys, for
1.41 stevesk 202: the passphrase if the key has one, and for the new comment.
1.66 jmc 203: .It Fl D Ar reader
204: Download the RSA public key stored in the smartcard in
205: .Ar reader .
1.37 markus 206: .It Fl e
1.40 markus 207: This option will read a private or public OpenSSH key file and
1.73 markus 208: print the key in
209: RFC 4716 SSH Public Key File Format
1.37 markus 210: to stdout.
211: This option allows exporting keys for use by several commercial
212: SSH implementations.
1.66 jmc 213: .It Fl F Ar hostname
214: Search for the specified
215: .Ar hostname
216: in a
217: .Pa known_hosts
218: file, listing any occurrences found.
219: This option is useful to find hashed host names or addresses and may also be
220: used in conjunction with the
221: .Fl H
222: option to print found keys in a hashed format.
223: .It Fl f Ar filename
224: Specifies the filename of the key file.
225: .It Fl G Ar output_file
226: Generate candidate primes for DH-GEX.
227: These primes must be screened for
228: safety (using the
229: .Fl T
230: option) before use.
1.57 jakob 231: .It Fl g
1.62 jakob 232: Use generic DNS format when printing fingerprint resource records using the
1.63 jmc 233: .Fl r
1.62 jakob 234: command.
1.66 jmc 235: .It Fl H
236: Hash a
237: .Pa known_hosts
1.67 dtucker 238: file.
239: This replaces all hostnames and addresses with hashed representations
240: within the specified file; the original content is moved to a file with
241: a .old suffix.
1.66 jmc 242: These hashes may be used normally by
243: .Nm ssh
244: and
245: .Nm sshd ,
246: but they do not reveal identifying information should the file's contents
247: be disclosed.
248: This option will not modify existing hashed hostnames and is therefore safe
249: to use on files that mix hashed and non-hashed names.
1.37 markus 250: .It Fl i
251: This option will read an unencrypted private (or public) key file
252: in SSH2-compatible format and print an OpenSSH compatible private
253: (or public) key to stdout.
254: .Nm
1.38 markus 255: also reads the
1.74 jmc 256: RFC 4716 SSH Public Key File Format.
1.37 markus 257: This option allows importing keys from several commercial
258: SSH implementations.
1.9 markus 259: .It Fl l
1.76 ! grunk 260: Show fingerprint and ASCII art representation of specified public key file.
1.50 markus 261: Private RSA1 keys are also supported.
262: For RSA and DSA keys
263: .Nm
1.76 ! grunk 264: tries to find the matching public key file and prints its fingerprint
! 265: and representation.
1.66 jmc 266: .It Fl M Ar memory
267: Specify the amount of memory to use (in megabytes) when generating
268: candidate moduli for DH-GEX.
269: .It Fl N Ar new_passphrase
270: Provides the new passphrase.
271: .It Fl P Ar passphrase
272: Provides the (old) passphrase.
1.2 deraadt 273: .It Fl p
1.1 deraadt 274: Requests changing the passphrase of a private key file instead of
1.12 aaron 275: creating a new private key.
276: The program will prompt for the file
1.1 deraadt 277: containing the private key, for the old passphrase, and twice for the
278: new passphrase.
1.5 aaron 279: .It Fl q
280: Silence
281: .Nm ssh-keygen .
282: Used by
283: .Pa /etc/rc
284: when creating a new key.
1.64 djm 285: .It Fl R Ar hostname
286: Removes all keys belonging to
287: .Ar hostname
1.65 jmc 288: from a
1.64 djm 289: .Pa known_hosts
290: file.
1.65 jmc 291: This option is useful to delete hashed hosts (see the
1.64 djm 292: .Fl H
293: option above).
1.66 jmc 294: .It Fl r Ar hostname
295: Print the SSHFP fingerprint resource record named
296: .Ar hostname
297: for the specified public key file.
1.60 djm 298: .It Fl S Ar start
299: Specify start point (in hex) when generating candidate moduli for DH-GEX.
300: .It Fl T Ar output_file
301: Test DH group exchange candidate primes (generated using the
302: .Fl G
303: option) for safety.
1.66 jmc 304: .It Fl t Ar type
305: Specifies the type of key to create.
306: The possible values are
307: .Dq rsa1
308: for protocol version 1 and
309: .Dq rsa
310: or
311: .Dq dsa
312: for protocol version 2.
1.48 jakob 313: .It Fl U Ar reader
314: Upload an existing RSA private key into the smartcard in
315: .Ar reader .
1.61 djm 316: .It Fl v
317: Verbose mode.
318: Causes
319: .Nm
320: to print debugging messages about its progress.
321: This is helpful for debugging moduli generation.
322: Multiple
323: .Fl v
324: options increase the verbosity.
325: The maximum is 3.
1.66 jmc 326: .It Fl W Ar generator
327: Specify desired generator when testing candidate moduli for DH-GEX.
328: .It Fl y
329: This option will read a private
330: OpenSSH format file and print an OpenSSH public key to stdout.
1.2 deraadt 331: .El
1.60 djm 332: .Sh MODULI GENERATION
333: .Nm
334: may be used to generate groups for the Diffie-Hellman Group Exchange
335: (DH-GEX) protocol.
336: Generating these groups is a two-step process: first, candidate
337: primes are generated using a fast, but memory intensive process.
338: These candidate primes are then tested for suitability (a CPU-intensive
339: process).
340: .Pp
341: Generation of primes is performed using the
342: .Fl G
343: option.
344: The desired length of the primes may be specified by the
345: .Fl b
346: option.
347: For example:
348: .Pp
1.66 jmc 349: .Dl # ssh-keygen -G moduli-2048.candidates -b 2048
1.60 djm 350: .Pp
351: By default, the search for primes begins at a random point in the
352: desired length range.
353: This may be overridden using the
354: .Fl S
355: option, which specifies a different start point (in hex).
356: .Pp
357: Once a set of candidates have been generated, they must be tested for
358: suitability.
359: This may be performed using the
360: .Fl T
361: option.
362: In this mode
363: .Nm
364: will read candidates from standard input (or a file specified using the
365: .Fl f
366: option).
367: For example:
368: .Pp
1.66 jmc 369: .Dl # ssh-keygen -T moduli-2048 -f moduli-2048.candidates
1.60 djm 370: .Pp
371: By default, each candidate will be subjected to 100 primality tests.
372: This may be overridden using the
373: .Fl a
374: option.
375: The DH generator value will be chosen automatically for the
376: prime under consideration.
377: If a specific generator is desired, it may be requested using the
378: .Fl W
379: option.
1.66 jmc 380: Valid generator values are 2, 3, and 5.
1.60 djm 381: .Pp
382: Screened DH groups may be installed in
383: .Pa /etc/moduli .
384: It is important that this file contains moduli of a range of bit lengths and
385: that both ends of a connection share common moduli.
1.2 deraadt 386: .Sh FILES
387: .Bl -tag -width Ds
1.68 djm 388: .It Pa ~/.ssh/identity
1.36 itojun 389: Contains the protocol version 1 RSA authentication identity of the user.
1.12 aaron 390: This file should not be readable by anyone but the user.
391: It is possible to
1.1 deraadt 392: specify a passphrase when generating the key; that passphrase will be
1.12 aaron 393: used to encrypt the private part of this file using 3DES.
394: This file is not automatically accessed by
1.2 deraadt 395: .Nm
1.1 deraadt 396: but it is offered as the default file for the private key.
1.46 markus 397: .Xr ssh 1
1.15 deraadt 398: will read this file when a login attempt is made.
1.68 djm 399: .It Pa ~/.ssh/identity.pub
1.36 itojun 400: Contains the protocol version 1 RSA public key for authentication.
1.12 aaron 401: The contents of this file should be added to
1.68 djm 402: .Pa ~/.ssh/authorized_keys
1.2 deraadt 403: on all machines
1.49 deraadt 404: where the user wishes to log in using RSA authentication.
1.15 deraadt 405: There is no need to keep the contents of this file secret.
1.68 djm 406: .It Pa ~/.ssh/id_dsa
1.36 itojun 407: Contains the protocol version 2 DSA authentication identity of the user.
1.15 deraadt 408: This file should not be readable by anyone but the user.
409: It is possible to
410: specify a passphrase when generating the key; that passphrase will be
411: used to encrypt the private part of this file using 3DES.
412: This file is not automatically accessed by
413: .Nm
414: but it is offered as the default file for the private key.
1.46 markus 415: .Xr ssh 1
1.15 deraadt 416: will read this file when a login attempt is made.
1.68 djm 417: .It Pa ~/.ssh/id_dsa.pub
1.36 itojun 418: Contains the protocol version 2 DSA public key for authentication.
419: The contents of this file should be added to
1.68 djm 420: .Pa ~/.ssh/authorized_keys
1.36 itojun 421: on all machines
1.49 deraadt 422: where the user wishes to log in using public key authentication.
1.36 itojun 423: There is no need to keep the contents of this file secret.
1.68 djm 424: .It Pa ~/.ssh/id_rsa
1.36 itojun 425: Contains the protocol version 2 RSA authentication identity of the user.
426: This file should not be readable by anyone but the user.
427: It is possible to
428: specify a passphrase when generating the key; that passphrase will be
429: used to encrypt the private part of this file using 3DES.
430: This file is not automatically accessed by
431: .Nm
432: but it is offered as the default file for the private key.
1.46 markus 433: .Xr ssh 1
1.36 itojun 434: will read this file when a login attempt is made.
1.68 djm 435: .It Pa ~/.ssh/id_rsa.pub
1.36 itojun 436: Contains the protocol version 2 RSA public key for authentication.
1.15 deraadt 437: The contents of this file should be added to
1.68 djm 438: .Pa ~/.ssh/authorized_keys
1.15 deraadt 439: on all machines
1.49 deraadt 440: where the user wishes to log in using public key authentication.
1.12 aaron 441: There is no need to keep the contents of this file secret.
1.60 djm 442: .It Pa /etc/moduli
443: Contains Diffie-Hellman groups used for DH-GEX.
444: The file format is described in
445: .Xr moduli 5 .
1.19 aaron 446: .El
1.2 deraadt 447: .Sh SEE ALSO
448: .Xr ssh 1 ,
449: .Xr ssh-add 1 ,
1.8 ericj 450: .Xr ssh-agent 1 ,
1.60 djm 451: .Xr moduli 5 ,
1.30 itojun 452: .Xr sshd 8
1.37 markus 453: .Rs
1.73 markus 454: .%R RFC 4716
455: .%T "The Secure Shell (SSH) Public Key File Format"
456: .%D 2006
1.37 markus 457: .Re
1.59 jmc 458: .Sh AUTHORS
459: OpenSSH is a derivative of the original and free
460: ssh 1.2.12 release by Tatu Ylonen.
461: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
462: Theo de Raadt and Dug Song
463: removed many bugs, re-added newer features and
464: created OpenSSH.
465: Markus Friedl contributed the support for SSH
466: protocol versions 1.5 and 2.0.
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