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Linux 2.6 - man page for crypt (linux section 3posix)

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

       crypt - string encoding function (CRYPT)

       #include <unistd.h>

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

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

       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 reen-
       trant is not required to be thread-safe.

       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.

       The crypt() function shall fail if:

       ENOSYS The functionality is not supported on this implementation.

       The following sections are informative.

   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 data-
       base. 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);

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



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

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					 CRYPT(P)

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