1 .\" FreeSec: libcrypt for NetBSD
3 .\" Copyright (c) 1994 David Burren
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37 .Nd Trapdoor encryption
43 .Fn crypt "const char *key" "const char *salt"
45 .Fn crypt_get_format "void"
47 .Fn crypt_set_format "const char *string"
51 function performs password hashing with additional code added to
52 deter key search attempts.
53 Different algorithms can be used to
57 .\" If you add more algorithms, make sure to update this list
58 .\" and the default used for the Traditional format, below.
60 Currently these include the
62 .Tn Data Encryption Standard (DES) ,
66 .Pq compatible with Microsoft's NT scheme
69 The algorithm used will depend upon the format of the Salt
72 the Modular Crypt Format
79 is installed or not, and whether
81 has been called to change the default.
86 .Pq usually a password ,
88 .Dv NUL Ns -terminated
90 The second is the salt, in one of three forms:
92 .Bl -tag -width Traditional -compact -offset indent
94 If it begins with an underscore
99 is used in interpreting both the key and the salt, as outlined below.
101 If it begins with the string
103 then the Modular Crypt Format is used, as outlined below.
105 If neither of the above is true, it assumes the Traditional Format,
106 using the entire string as the salt
107 .Pq or the first portion .
110 All routines are designed to be time-consuming.
111 .Ss DES Extended Format:
114 is divided into groups of 8 characters
115 .Pq the last group is NUL-padded
116 and the low-order 7 bits of each character
117 .Pq 56 bits per group
121 the first group of 56 bits becomes the initial
124 For each additional group, the XOR of the encryption of the current
126 key with itself and the group bits becomes the next
130 The salt is a 9-character array consisting of an underscore followed
131 by 4 bytes of iteration count and 4 bytes of salt.
132 These are encoded as printable characters, 6 bits per character,
133 least significant character first.
134 The values 0 to 63 are encoded as
136 This allows 24 bits for both
143 introduces disorder in the
145 algorithm in one of 16777216 or 4096 possible ways
147 i.e., with 24 or 12 bits: if bit
162 key is used to encrypt a 64-bit constant using
166 The value returned is a
167 .Dv NUL Ns -terminated
168 string, 20 or 13 bytes
170 in length, consisting of the
172 followed by the encoded 64-bit encryption.
174 If the salt begins with the string
176 then the Modular Crypt Format is used.
179 represents which algorithm is used in encryption.
180 Following the token is
181 the actual salt to use in the encryption.
182 The maximum length of the salt used depends upon the module.
183 The salt must be terminated with the end of the string character
186 Any characters after the dollar sign are ignored.
188 Currently supported algorithms are:
190 .Bl -enum -compact -offset indent
205 Other crypt formats may be easily added.
206 An example salt would be:
207 .Bl -tag -width 6n -offset indent
208 .It Cm "$4$thesalt$rest"
210 .Ss Traditional crypt:
211 The algorithm used will depend upon whether
213 has been called and whether a global default format has been specified.
214 Unless a global default has been specified or
216 has set the format to something else, the built-in default format is
220 .\" NOTICE: Also make sure to update this
223 if it is available, or MD5 if not.
225 How the salt is used will depend upon the algorithm for the hash.
227 best results, specify at least eight characters of salt.
231 function returns a constant string that represents the name of the
232 algorithm currently used.
235 .\" NOTICE: Also make sure to update this, too, as well
247 function sets the default encoding format according to the supplied
252 function returns a pointer to the encrypted value on success, and NULL on
254 Note: this is not a standard behaviour, AT&T
256 will always return a pointer to a string.
260 function will return 1 if the supplied encoding format was valid.
261 Otherwise, a value of 0 is returned.
279 section of the code (FreeSec 1.0) was developed outside the United
280 States of America as an unencumbered replacement for the U.S.-only
282 libcrypt encryption library.
285 Originally written by
286 .An David Burren Aq davidb@werj.com.au ,
287 later additions and changes by
288 .An Poul-Henning Kamp ,
289 .An Mark R V Murray ,
290 .An Michael Bretterklieber ,
299 function returns a pointer to static data, and subsequent calls to
301 will modify the same data.
304 modifies static data.
306 The NT-hash scheme does not use a salt,
308 for a competent attacker
310 Its use is not recommended.