Add sha256/512 support to libcrypt, change default
[dragonfly.git] / lib / libcrypt / crypt.3
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1.\" FreeSec: libcrypt for NetBSD
2.\"
3.\" Copyright (c) 1994 David Burren
4.\" All rights reserved.
5.\"
6.\" Redistribution and use in source and binary forms, with or without
7.\" modification, are permitted provided that the following conditions
8.\" are met:
9.\" 1. Redistributions of source code must retain the above copyright
10.\" notice, this list of conditions and the following disclaimer.
11.\" 2. Redistributions in binary form must reproduce the above copyright
12.\" notice, this list of conditions and the following disclaimer in the
13.\" documentation and/or other materials provided with the distribution.
14.\" 4. Neither the name of the author nor the names of other contributors
15.\" may be used to endorse or promote products derived from this software
16.\" without specific prior written permission.
17.\"
18.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28.\" SUCH DAMAGE.
29.\"
30.\" $FreeBSD: src/lib/libcrypt/crypt.3,v 1.6.2.14 2002/12/29 16:35:35 schweikh Exp $
c2cd059b 31.\" $DragonFly: src/lib/libcrypt/crypt.3,v 1.5 2006/03/26 22:56:56 swildner Exp $
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32.\"
33.\" Manual page, using -mandoc macros
34.\"
35.Dd January 19, 1997
36.Dt CRYPT 3
37.Os
38.Sh NAME
39.Nm crypt
40.Nd Trapdoor encryption
41.Sh LIBRARY
42.Lb libcrypt
43.Sh SYNOPSIS
44.In unistd.h
45.Ft char *
46.Fn crypt "const char *key" "const char *salt"
47.Ft const char *
48.Fn crypt_get_format "void"
49.Ft int
50.Fn crypt_set_format "const char *string"
51.Sh DESCRIPTION
52The
53.Fn crypt
54function performs password hashing with additional code added to
55deter key search attempts. Different algorithms can be used to
56in the hash.
57.\"
58.\" NOTICE:
59.\" If you add more algorithms, make sure to update this list
60.\" and the default used for the Traditional format, below.
61.\"
62Currently these include the
63.Tn NBS
64.Tn Data Encryption Standard (DES) ,
65.Tn MD5
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66.Tn SHA256
67.Tn SHA512
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68and
69.Tn Blowfish .
70The algorithm used will depend upon the format of the Salt (following
71the Modular Crypt Format (MCF)), if
72.Tn DES
73and/or
74.Tn Blowfish
75is installed or not, and whether
76.Fn crypt_set_format
77has been called to change the default.
78.Pp
79The first argument to
80.Nm
81is the data to hash (usually a password), in a
82.Dv null Ns -terminated
83string.
84The second is the salt, in one of three forms:
85.Pp
86.Bl -tag -width Traditional -compact -offset indent
87.It Extended
88If it begins with an underscore
89.Pq Dq _
90then the
91.Tn DES
92Extended Format
93is used in interpreting both the key and the salt, as outlined below.
94.It Modular
95If it begins with the string
96.Dq $digit$
97then the Modular Crypt Format is used, as outlined below.
98.It Traditional
99If neither of the above is true, it assumes the Traditional Format,
100using the entire string as the salt (or the first portion).
101.El
102.Pp
103All routines are designed to be time-consuming. A brief test on a
104.Tn Pentium
105166/MMX shows the
106.Tn DES
107crypt to do approximately 2640 crypts
108a CPU second and MD5 to do about 62 crypts a CPU second.
109.Ss DES Extended Format:
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110The
111.Ar key
112is divided into groups of 8 characters (the last group is null-padded)
113and the low-order 7 bits of each character (56 bits per group) are
114used to form the
115.Tn DES
116key as follows:
117the first group of 56 bits becomes the initial
118.Tn DES
119key.
120For each additional group, the XOR of the encryption of the current
121.Tn DES
122key with itself and the group bits becomes the next
123.Tn DES
124key.
125.Pp
126The salt is a 9-character array consisting of an underscore followed
127by 4 bytes of iteration count and 4 bytes of salt.
128These are encoded as printable characters, 6 bits per character,
129least significant character first.
130The values 0 to 63 are encoded as ``./0-9A-Za-z''.
131This allows 24 bits for both
132.Fa count
133and
134.Fa salt .
135.Pp
136The
137.Fa salt
138introduces disorder in the
139.Tn DES
140algorithm in one of 16777216 or 4096 possible ways
141(ie. with 24 or 12 bits: if bit
142.Em i
143of the
144.Ar salt
145is set, then bits
146.Em i
147and
148.Em i+24
149are swapped in the
150.Tn DES
151E-box output).
152.Pp
153The
154.Tn DES
155key is used to encrypt a 64-bit constant using
156.Ar count
157iterations of
158.Tn DES .
159The value returned is a
160.Dv null Ns -terminated
161string, 20 or 13 bytes (plus null) in length, consisting of the
162.Ar salt
163followed by the encoded 64-bit encryption.
164.Ss "Modular" crypt:
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165If the salt begins with the string
166.Fa $digit$
167then the Modular Crypt Format is used. The
168.Fa digit
169represents which algorithm is used in encryption. Following the token is
170the actual salt to use in the encryption. The length of the salt is limited
171to 8 characters--because the length of the returned output is also limited
172(_PASSWORD_LEN). The salt must be terminated with the end of the string
173(NULL) or a dollar sign. Any characters after the dollar sign are ignored.
174.Pp
175Currently supported algorithms are:
176.Pp
177.Bl -enum -compact -offset indent
178.It
179MD5
180.It
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181SHA256
182.It
183SHA512
184.It
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185Blowfish
186.El
187.Pp
188Other crypt formats may be easily added. An example salt would be:
189.Bl -tag -offset indent
190.It Cm "$3$thesalt$rest"
191.El
984263bc 192.Ss "Traditional" crypt:
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193The algorithm used will depend upon whether
194.Fn crypt_set_format
195has been called and whether a global default format has been specified.
196Unless a global default has been specified or
197.Fn crypt_set_format
198has set the format to something else, the built-in default format is
199used.
200This is currently
201.\"
202.\" NOTICE: Also make sure to update this
203.\"
204DES
205if it is available, or MD5 if not.
206.Pp
207How the salt is used will depend upon the algorithm for the hash. For
208best results, specify at least two characters of salt.
209.Pp
210The
211.Fn crypt_get_format
212function returns a constant string that represents the name of the
213algorithm currently used.
214Valid values are
215.\"
216.\" NOTICE: Also make sure to update this, too, as well
217.\"
218.Ql des ,
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219.Ql blf ,
220.Ql sha256 ,
221.Ql sha512 ,
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222and
223.Ql md5 .
224.Pp
225The
226.Fn crypt_set_format
227function sets the default encoding format according to the supplied
228.Fa string .
229.Pp
230The global default format can be set using the
231.Pa /etc/auth.conf
232file using the
233.Va crypt_default
234property.
235.Sh RETURN VALUES
236.Fn crypt
237returns a pointer to the encrypted value on success, and NULL on failure.
238Note: this is not a standard behaviour, AT&T
239.Fn crypt
240will always return a pointer to a string.
241.Pp
242.Fn crypt_set_format
243will return 1 if the supplied encoding format was valid.
244Otherwise, a value of 0 is returned.
245.Sh SEE ALSO
246.Xr login 1 ,
247.Xr passwd 1 ,
248.Xr auth_getval 3 ,
249.Xr cipher 3 ,
250.Xr getpass 3 ,
251.Xr auth.conf 5 ,
252.Xr passwd 5
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253.Sh HISTORY
254A rotor-based
255.Fn crypt
256function appeared in
257.At v6 .
258The current style
259.Fn crypt
260first appeared in
261.At v7 .
262.Pp
263The
264.Tn DES
265section of the code (FreeSec 1.0) was developed outside the United
266States of America as an unencumbered replacement for the U.S.-only
267.Nx
268libcrypt encryption library.
269.Sh AUTHORS
270.An -nosplit
271Originally written by
272.An David Burren Aq davidb@werj.com.au ,
273later additions and changes by
274.An Poul-Henning Kamp ,
275.An Mark R V Murray ,
276.An Kris Kennaway ,
277.An Brian Feldman ,
278.An Paul Herman
279and
280.An Niels Provos .
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281.Sh BUGS
282The
283.Fn crypt
284function returns a pointer to static data, and subsequent calls to
285.Fn crypt
286will modify the same data. Likewise,
287.Fn crypt_set_format
288modifies static data.