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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 (consult 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, Copyright (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.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                            CRYPT(3P)