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



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       crypt - string encoding function (CRYPT)

SYNOPSIS
       #include <unistd.h>

       char *crypt(const char *key, const char *salt);


DESCRIPTION
       The crypt() function is a string encoding function. The algorithm is implementation-defined.

       The key argument points to a string to be encoded. The salt argument is a string chosen from the set:


              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
              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
              0 1 2 3 4 5 6 7 8 9 . /

       The first two characters of this string may be used to perturb the encoding algorithm.

       The return value of crypt() points to static data that is overwritten by each call.

       The crypt() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-
       safe.

RETURN VALUE
       Upon successful completion, crypt() shall return a pointer to the  encoded  string.  The  first  two  characters  of  the
       returned  value  shall be those of the salt argument. Otherwise, it shall return a null pointer and set errno to indicate
       the error.

ERRORS
       The crypt() function shall fail if:

       ENOSYS The functionality is not supported on this implementation.


       The following sections are informative.

EXAMPLES
   Encoding Passwords
       The following example finds a user database entry matching a particular user name and changes the current password  to  a
       new  password.  The crypt() function generates an encoded version of each password. The first call to crypt() produces an
       encoded version of the old password; that encoded password is then compared to the password stored in the user  database.
       The second call to crypt() encodes the new password before it is stored.

       The putpwent() function, used in the following example, is not part of IEEE Std 1003.1-2001.


              #include <unistd.h>
              #include <pwd.h>
              #include <string.h>
              #include <stdio.h>
              ...
              int valid_change;
              int pfd;  /* Integer for file descriptor returned by open(). */
              FILE *fpfd;  /* File pointer for use in putpwent(). */
              struct passwd *p;
              char user[100];
              char oldpasswd[100];
              char newpasswd[100];
              char savepasswd[100];
              ...
              valid_change = 0;
              while ((p = getpwent()) != NULL) {
                  /* Change entry if found. */
                  if (strcmp(p->pw_name, user) == 0) {
                      if (strcmp(p->pw_passwd, crypt(oldpasswd, p->pw_passwd)) == 0) {
                          strcpy(savepasswd, crypt(newpasswd, user));
                          p->pw_passwd = savepasswd;
                          valid_change = 1;
                      }
                      else {
                          fprintf(stderr, "Old password is not valid\n");
                      }
                  }
                  /* Put passwd entry into ptmp. */
                  putpwent(p, fpfd);
              }

APPLICATION USAGE
       The values returned by this function need not be portable among XSI-conformant systems.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       encrypt(), setkey(), the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open  Group
       Standard   is   the   referee   document.   The   original   Standard   can   be   obtained  online  at  http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                     CRYPT(3P)