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 (compatible with Microsoft's NT scheme)
69 The algorithm used will depend upon the format of the Salt (following
70 the Modular Crypt Format (MCF)), if
74 is installed or not, and whether
76 has been called to change the default.
80 is the data to hash (usually a password), in a
81 .Dv null Ns -terminated
83 The second is the salt, in one of three forms:
85 .Bl -tag -width Traditional -compact -offset indent
87 If it begins with an underscore
92 is used in interpreting both the key and the salt, as outlined below.
94 If it begins with the string
96 then the Modular Crypt Format is used, as outlined below.
98 If neither of the above is true, it assumes the Traditional Format,
99 using the entire string as the salt (or the first portion).
102 All routines are designed to be time-consuming.
107 crypt to do approximately 2640 crypts
108 a CPU second and MD5 to do about 62 crypts a CPU second.
109 .Ss DES Extended Format:
112 is divided into groups of 8 characters (the last group is null-padded)
113 and the low-order 7 bits of each character (56 bits per group) are
117 the first group of 56 bits becomes the initial
120 For each additional group, the XOR of the encryption of the current
122 key with itself and the group bits becomes the next
126 The salt is a 9-character array consisting of an underscore followed
127 by 4 bytes of iteration count and 4 bytes of salt.
128 These are encoded as printable characters, 6 bits per character,
129 least significant character first.
130 The values 0 to 63 are encoded as ``./0-9A-Za-z''.
131 This allows 24 bits for both
138 introduces disorder in the
140 algorithm in one of 16777216 or 4096 possible ways
141 (i.e., with 24 or 12 bits: if bit
155 key is used to encrypt a 64-bit constant using
159 The value returned is a
160 .Dv null Ns -terminated
161 string, 20 or 13 bytes (plus null) in length, consisting of the
163 followed by the encoded 64-bit encryption.
165 If the salt begins with the string
167 then the Modular Crypt Format is used.
170 represents which algorithm is used in encryption.
171 Following the token is
172 the actual salt to use in the encryption.
173 The length of the salt is limited
174 to 8 characters--because the length of the returned output is also limited
176 The salt must be terminated with the end of the string
177 (NULL) or a dollar sign.
178 Any characters after the dollar sign are ignored.
180 Currently supported algorithms are:
182 .Bl -enum -compact -offset indent
197 Other crypt formats may be easily added.
198 An example salt would be:
199 .Bl -tag -offset indent
200 .It Cm "$4$thesalt$rest"
202 .Ss "Traditional" crypt:
203 The algorithm used will depend upon whether
205 has been called and whether a global default format has been specified.
206 Unless a global default has been specified or
208 has set the format to something else, the built-in default format is
212 .\" NOTICE: Also make sure to update this
215 if it is available, or MD5 if not.
217 How the salt is used will depend upon the algorithm for the hash.
219 best results, specify at least two characters of salt.
223 function returns a constant string that represents the name of the
224 algorithm currently used.
227 .\" NOTICE: Also make sure to update this, too, as well
239 function sets the default encoding format according to the supplied
242 The global default format can be set using the
250 function returns a pointer to the encrypted value on success, and NULL on
252 Note: this is not a standard behaviour, AT&T
254 will always return a pointer to a string.
258 function will return 1 if the supplied encoding format was valid.
259 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.