CRYPT(3P)

CRYPT(3P)

                  POSIX Programmer's Manual
                 CRYPT(3P)

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)

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