1CRYPT(3P) POSIX Programmer's Manual CRYPT(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 crypt - string encoding function (CRYPT)
13
15 #include <unistd.h>
16 char *crypt(const char *key, const char *salt);
18
21 The crypt() function is a string encoding function. The algorithm is
22 implementation-defined.
23 The key argument points to a string to be encoded. The salt argument is
25 a string chosen from the set:
26 a b c d e f g h i j k l m n o p q r s t u v w x y z
29 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
30 0 1 2 3 4 5 6 7 8 9 . /
31 The first two characters of this string may be used to perturb the
33 encoding algorithm.
34 The return value of crypt() points to static data that is overwritten
36 by each call.
37 The crypt() function need not be reentrant. A function that is not
39 required to be reentrant is not required to be thread-safe.
40
42 Upon successful completion, crypt() shall return a pointer to the
43 encoded string. The first two characters of the returned value shall be
44 those of the salt argument. Otherwise, it shall return a null pointer
45 and set errno to indicate the error.
46
48 The crypt() function shall fail if:
49 ENOSYS The functionality is not supported on this implementation.
51 The following sections are informative.
54
56 Encoding Passwords
57 The following example finds a user database entry matching a particular
58 user name and changes the current password to a new password. The
59 crypt() function generates an encoded version of each password. The
60 first call to crypt() produces an encoded version of the old password;
61 that encoded password is then compared to the password stored in the
62 user database. The second call to crypt() encodes the new password
63 before it is stored.
64 The putpwent() function, used in the following example, is not part of
66 IEEE Std 1003.1-2001.
67 #include <unistd.h>
70 #include <pwd.h>
71 #include <string.h>
72 #include <stdio.h>
73 ...
74 int valid_change;
75 int pfd; /* Integer for file descriptor returned by open(). */
76 FILE *fpfd; /* File pointer for use in putpwent(). */
77 struct passwd *p;
78 char user[100];
79 char oldpasswd[100];
80 char newpasswd[100];
81 char savepasswd[100];
82 ...
83 valid_change = 0;
84 while ((p = getpwent()) != NULL) {
85 /* Change entry if found. */
86 if (strcmp(p->pw_name, user) == 0) {
87 if (strcmp(p->pw_passwd, crypt(oldpasswd, p->pw_passwd)) == 0) {
88 strcpy(savepasswd, crypt(newpasswd, user));
89 p->pw_passwd = savepasswd;
90 valid_change = 1;
91 }
92 else {
93 fprintf(stderr, "Old password is not valid\n");
94 }
95 }
96 /* Put passwd entry into ptmp. */
97 putpwent(p, fpfd);
98 }
99
101 The values returned by this function need not be portable among XSI-
102 conformant systems.
103
105 None.
106
108 None.
109
111 encrypt(), setkey(), the Base Definitions volume of
112 IEEE Std 1003.1-2001, <unistd.h>
113
115 Portions of this text are reprinted and reproduced in electronic form
116 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
117 -- Portable Operating System Interface (POSIX), The Open Group Base
118 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
119 Electrical and Electronics Engineers, Inc and The Open Group. In the
120 event of any discrepancy between this version and the original IEEE and
121 The Open Group Standard, the original IEEE and The Open Group Standard
122 is the referee document. The original Standard can be obtained online
123 at http://www.opengroup.org/unix/online.html .
124IEEE/The Open Group 2003 CRYPT(3P)