How buggy this little piece of code could be? Repair strnvis() buffersize
[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
66and
67.Tn Blowfish .
68The algorithm used will depend upon the format of the Salt (following
69the Modular Crypt Format (MCF)), if
70.Tn DES
71and/or
72.Tn Blowfish
73is installed or not, and whether
74.Fn crypt_set_format
75has been called to change the default.
76.Pp
77The first argument to
78.Nm
79is the data to hash (usually a password), in a
80.Dv null Ns -terminated
81string.
82The second is the salt, in one of three forms:
83.Pp
84.Bl -tag -width Traditional -compact -offset indent
85.It Extended
86If it begins with an underscore
87.Pq Dq _
88then the
89.Tn DES
90Extended Format
91is used in interpreting both the key and the salt, as outlined below.
92.It Modular
93If it begins with the string
94.Dq $digit$
95then the Modular Crypt Format is used, as outlined below.
96.It Traditional
97If neither of the above is true, it assumes the Traditional Format,
98using the entire string as the salt (or the first portion).
99.El
100.Pp
101All routines are designed to be time-consuming. A brief test on a
102.Tn Pentium
103166/MMX shows the
104.Tn DES
105crypt to do approximately 2640 crypts
106a CPU second and MD5 to do about 62 crypts a CPU second.
107.Ss DES Extended Format:
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108The
109.Ar key
110is divided into groups of 8 characters (the last group is null-padded)
111and the low-order 7 bits of each character (56 bits per group) are
112used to form the
113.Tn DES
114key as follows:
115the first group of 56 bits becomes the initial
116.Tn DES
117key.
118For each additional group, the XOR of the encryption of the current
119.Tn DES
120key with itself and the group bits becomes the next
121.Tn DES
122key.
123.Pp
124The salt is a 9-character array consisting of an underscore followed
125by 4 bytes of iteration count and 4 bytes of salt.
126These are encoded as printable characters, 6 bits per character,
127least significant character first.
128The values 0 to 63 are encoded as ``./0-9A-Za-z''.
129This allows 24 bits for both
130.Fa count
131and
132.Fa salt .
133.Pp
134The
135.Fa salt
136introduces disorder in the
137.Tn DES
138algorithm in one of 16777216 or 4096 possible ways
139(ie. with 24 or 12 bits: if bit
140.Em i
141of the
142.Ar salt
143is set, then bits
144.Em i
145and
146.Em i+24
147are swapped in the
148.Tn DES
149E-box output).
150.Pp
151The
152.Tn DES
153key is used to encrypt a 64-bit constant using
154.Ar count
155iterations of
156.Tn DES .
157The value returned is a
158.Dv null Ns -terminated
159string, 20 or 13 bytes (plus null) in length, consisting of the
160.Ar salt
161followed by the encoded 64-bit encryption.
162.Ss "Modular" crypt:
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163If the salt begins with the string
164.Fa $digit$
165then the Modular Crypt Format is used. The
166.Fa digit
167represents which algorithm is used in encryption. Following the token is
168the actual salt to use in the encryption. The length of the salt is limited
169to 8 characters--because the length of the returned output is also limited
170(_PASSWORD_LEN). The salt must be terminated with the end of the string
171(NULL) or a dollar sign. Any characters after the dollar sign are ignored.
172.Pp
173Currently supported algorithms are:
174.Pp
175.Bl -enum -compact -offset indent
176.It
177MD5
178.It
179Blowfish
180.El
181.Pp
182Other crypt formats may be easily added. An example salt would be:
183.Bl -tag -offset indent
184.It Cm "$3$thesalt$rest"
185.El
984263bc 186.Ss "Traditional" crypt:
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187The algorithm used will depend upon whether
188.Fn crypt_set_format
189has been called and whether a global default format has been specified.
190Unless a global default has been specified or
191.Fn crypt_set_format
192has set the format to something else, the built-in default format is
193used.
194This is currently
195.\"
196.\" NOTICE: Also make sure to update this
197.\"
198DES
199if it is available, or MD5 if not.
200.Pp
201How the salt is used will depend upon the algorithm for the hash. For
202best results, specify at least two characters of salt.
203.Pp
204The
205.Fn crypt_get_format
206function returns a constant string that represents the name of the
207algorithm currently used.
208Valid values are
209.\"
210.\" NOTICE: Also make sure to update this, too, as well
211.\"
212.Ql des ,
213.Ql blf
214and
215.Ql md5 .
216.Pp
217The
218.Fn crypt_set_format
219function sets the default encoding format according to the supplied
220.Fa string .
221.Pp
222The global default format can be set using the
223.Pa /etc/auth.conf
224file using the
225.Va crypt_default
226property.
227.Sh RETURN VALUES
228.Fn crypt
229returns a pointer to the encrypted value on success, and NULL on failure.
230Note: this is not a standard behaviour, AT&T
231.Fn crypt
232will always return a pointer to a string.
233.Pp
234.Fn crypt_set_format
235will return 1 if the supplied encoding format was valid.
236Otherwise, a value of 0 is returned.
237.Sh SEE ALSO
238.Xr login 1 ,
239.Xr passwd 1 ,
240.Xr auth_getval 3 ,
241.Xr cipher 3 ,
242.Xr getpass 3 ,
243.Xr auth.conf 5 ,
244.Xr passwd 5
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245.Sh HISTORY
246A rotor-based
247.Fn crypt
248function appeared in
249.At v6 .
250The current style
251.Fn crypt
252first appeared in
253.At v7 .
254.Pp
255The
256.Tn DES
257section of the code (FreeSec 1.0) was developed outside the United
258States of America as an unencumbered replacement for the U.S.-only
259.Nx
260libcrypt encryption library.
261.Sh AUTHORS
262.An -nosplit
263Originally written by
264.An David Burren Aq davidb@werj.com.au ,
265later additions and changes by
266.An Poul-Henning Kamp ,
267.An Mark R V Murray ,
268.An Kris Kennaway ,
269.An Brian Feldman ,
270.An Paul Herman
271and
272.An Niels Provos .
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273.Sh BUGS
274The
275.Fn crypt
276function returns a pointer to static data, and subsequent calls to
277.Fn crypt
278will modify the same data. Likewise,
279.Fn crypt_set_format
280modifies static data.