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:
113 is divided into groups of 8 characters (the last group is null-padded)
114 and the low-order 7 bits of each character (56 bits per group) are
118 the first group of 56 bits becomes the initial
121 For each additional group, the XOR of the encryption of the current
123 key with itself and the group bits becomes the next
127 The salt is a 9-character array consisting of an underscore followed
128 by 4 bytes of iteration count and 4 bytes of salt.
129 These are encoded as printable characters, 6 bits per character,
130 least significant character first.
131 The values 0 to 63 are encoded as ``./0-9A-Za-z''.
132 This allows 24 bits for both
139 introduces disorder in the
141 algorithm in one of 16777216 or 4096 possible ways
142 (i.e., with 24 or 12 bits: if bit
156 key is used to encrypt a 64-bit constant using
160 The value returned is a
161 .Dv null Ns -terminated
162 string, 20 or 13 bytes (plus null) in length, consisting of the
164 followed by the encoded 64-bit encryption.
167 If the salt begins with the string
169 then the Modular Crypt Format is used.
172 represents which algorithm is used in encryption.
173 Following the token is
174 the actual salt to use in the encryption.
175 The length of the salt is limited
176 to 8 characters--because the length of the returned output is also limited
178 The salt must be terminated with the end of the string
179 (NULL) or a dollar sign.
180 Any characters after the dollar sign are ignored.
182 Currently supported algorithms are:
184 .Bl -enum -compact -offset indent
199 Other crypt formats may be easily added.
200 An example salt would be:
201 .Bl -tag -offset indent
202 .It Cm "$4$thesalt$rest"
205 .Ss "Traditional" crypt:
207 The algorithm used will depend upon whether
209 has been called and whether a global default format has been specified.
210 Unless a global default has been specified or
212 has set the format to something else, the built-in default format is
216 .\" NOTICE: Also make sure to update this
219 if it is available, or MD5 if not.
221 How the salt is used will depend upon the algorithm for the hash.
223 best results, specify at least two characters of salt.
227 function returns a constant string that represents the name of the
228 algorithm currently used.
231 .\" NOTICE: Also make sure to update this, too, as well
243 function sets the default encoding format according to the supplied
248 function returns a pointer to the encrypted value on success, and NULL on
250 Note: this is not a standard behaviour, AT&T
252 will always return a pointer to a string.
256 function will return 1 if the supplied encoding format was valid.
257 Otherwise, a value of 0 is returned.
275 section of the code (FreeSec 1.0) was developed outside the United
276 States of America as an unencumbered replacement for the U.S.-only
278 libcrypt encryption library.
281 Originally written by
282 .An David Burren Aq davidb@werj.com.au ,
283 later additions and changes by
284 .An Poul-Henning Kamp ,
285 .An Mark R V Murray ,
286 .An Michael Bretterklieber ,
295 function returns a pointer to static data, and subsequent calls to
297 will modify the same data.
300 modifies static data.
302 The NT-hash scheme does not use a salt,
304 for a competent attacker
306 Its use is not recommended.