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1 perry 1 CRYPT
2 !!!CRYPT
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 RETURN VALUE
7 ERRORS
8 CONFORMING TO
9 SEE ALSO
10 ----
11 !!NAME
12
13
14 crypt - password and data encryption
15 !!SYNOPSIS
16
17
18 __#include __
19
20
21 __char *crypt(const char *__''key''__, const char
22 *__''salt''__);__
23 !!DESCRIPTION
24
25
26 __crypt__ provides acess to two algorithms for password
27 encryption. One it's based on the Data Encryption Standard
28 algorithm with variations intended (among other things) to
29 discourage use of hardware implementations of a key
30 search.
31
32
33 ''key'' is a user's typed password.
34
35
36 ''salt'' is a two-character string chosen from the set
37 [[__a__-__zA__-__Z0__-__9./__]. This string is
38 used to perturb the algorithm in one of 4096 different
39 ways.
40
41
42 By taking the lowest 7 bit of each character of the
43 ''key'', a 56-bit key is obtained. This 56-bit key is
44 used to encrypt repeatedly a constant string (usually a
45 string consisting of all zeros). The returned value points
46 to the encrypted password, a series of 13 printable ASCII
47 characters (the first two characters represent the salt
48 itself). The return value points to static data whose
49 content is overwritten by each call.
50
51
52 Warning: The key space consists of 2 56 equal
53 7.2e16 possible values. Exhaustive searches of this key
54 space are possible using massively parallel computers.
55 Software, such as crack(1), is available which will
56 search the portion of this key space that is generally used
57 by humans for passwords. Hence, password selection should,
58 at minimum, avoid common words and names. The use of a
59 passwd(1) program that checks for crackable passwords
60 during the selection process is recommended.
61
62
63 The DES algorithm itself has a few quirks which make the use
64 of the crypt(3) interface a very poor choice for
65 anything other than password authentication. If you are
66 planning on using the crypt(3) interface for a
67 cryptography project, don't do it: get a good book on
68 encryption and one of the widely available DES
69 libraries.
70 !!RETURN VALUE
71
72
73 A pointer to the encrypted password is returned. On error,
74 NULL is returned.
75 !!ERRORS
76
77
78 __ENOSYS__
79
80
81 The __crypt__ function was not implemented, probably
82 because of U.S.A. export restrictions.
83
84
85 If the salt starts with ''$1$'' an MD5 based password
86 hashing algorithm is applied. The salt should consist off
87 ''$1$'' followed with eight characters.
88
89
90 Programs using this function must be linked with
91 -lcrypt.
92 !!CONFORMING TO
93
94
95 SVID, X/OPEN, BSD 4.3
96 !!SEE ALSO
97
98
99 login(1), passwd(1), encrypt(3),
100 getpass(3), passwd(5)
101 ----
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