posix man page for crypt

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 correspond-
       ing 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 shall be a string of at least two bytes in length  not  including  the
       null character 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 bytes 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 thread-safe.

RETURN VALUE
       Upon  successful completion, crypt() shall return a pointer to the encoded string. The first two bytes 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 POSIX.1-2008.

	   #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
");
		   }
	       }
	       /* 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 POSIX.1-2008, <unistd.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013								 CRYPT(3P)