1CRYPT(3P)                  POSIX Programmer's Manual                 CRYPT(3P)
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PROLOG

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.
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11

NAME

13       crypt — string encoding function (CRYPT)
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SYNOPSIS

16       #include <unistd.h>
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18       char *crypt(const char *key, const char *salt);
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DESCRIPTION

21       The crypt() function is a string encoding function.  The  algorithm  is
22       implementation-defined.
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24       The  key  argument  points to a string to be encoded. The salt argument
25       shall be a string of at least two bytes in  length  not  including  the
26       null character chosen from the set:
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28           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 . /
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32       The  first two bytes of this string may be used to perturb the encoding
33       algorithm.
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35       The return value of crypt() points to static data that  is  overwritten
36       by each call.
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38       The crypt() function need not be thread-safe.
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RETURN VALUE

41       Upon  successful  completion,  crypt()  shall  return  a pointer to the
42       encoded string. The first two bytes of  the  returned  value  shall  be
43       those  of  the salt argument. Otherwise, it shall return a null pointer
44       and set errno to indicate the error.
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ERRORS

47       The crypt() function shall fail if:
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49       ENOSYS The functionality is not supported on this implementation.
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51       The following sections are informative.
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EXAMPLES

54   Encoding Passwords
55       The following example finds a user database entry matching a particular
56       user  name  and  changes  the  current  password to a new password. The
57       crypt() function generates an encoded version  of  each  password.  The
58       first  call to crypt() produces an encoded version of the old password;
59       that encoded password is then compared to the password  stored  in  the
60       user  database.  The  second  call  to crypt() encodes the new password
61       before it is stored.
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63       The putpwent() function, used in the following example, is not part  of
64       POSIX.1‐2008.
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66           #include <unistd.h>
67           #include <pwd.h>
68           #include <string.h>
69           #include <stdio.h>
70           ...
71           int valid_change;
72           int pfd;  /* Integer for file descriptor returned by open(). */
73           FILE *fpfd;  /* File pointer for use in putpwent(). */
74           struct passwd *p;
75           char user[100];
76           char oldpasswd[100];
77           char newpasswd[100];
78           char savepasswd[100];
79           ...
80           valid_change = 0;
81           while ((p = getpwent()) != NULL) {
82               /* Change entry if found. */
83               if (strcmp(p->pw_name, user) == 0) {
84                   if (strcmp(p->pw_passwd, crypt(oldpasswd, p->pw_passwd)) == 0) {
85                       strcpy(savepasswd, crypt(newpasswd, user));
86                       p->pw_passwd = savepasswd;
87                       valid_change = 1;
88                   }
89                   else {
90                       fprintf(stderr, "Old password is not valid\n");
91                   }
92               }
93               /* Put passwd entry into ptmp. */
94               putpwent(p, fpfd);
95           }
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APPLICATION USAGE

98       The  values  returned  by this function need not be portable among XSI-
99       conformant systems.
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RATIONALE

102       None.
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FUTURE DIRECTIONS

105       None.
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SEE ALSO

108       encrypt(), setkey()
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110       The Base Definitions volume of POSIX.1‐2008, <unistd.h>
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113       Portions of this text are reprinted and reproduced in  electronic  form
114       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
115       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
116       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
117       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
118       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
119       event of any discrepancy between this version and the original IEEE and
120       The  Open Group Standard, the original IEEE and The Open Group Standard
121       is the referee document. The original Standard can be  obtained  online
122       at http://www.unix.org/online.html .
123
124       Any  typographical  or  formatting  errors that appear in this page are
125       most likely to have been introduced during the conversion of the source
126       files  to  man page format. To report such errors, see https://www.ker
127       nel.org/doc/man-pages/reporting_bugs.html .
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131IEEE/The Open Group                  2013                            CRYPT(3P)
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