0x760. Password Cracking

Passwords aren't generally stored in plaintext form. A file containing all the passwords in plaintext form would be far too attractive a target, so instead, a one-way hash function is used. The best-known of these functions is based on DES and is called crypt(), which is described in the manual page shown below.

NAME
       crypt - password and data encryption

SYNOPSIS
       #define _XOPEN_SOURCE
       #include <unistd.h>

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

DESCRIPTION
       crypt()  is  the  password  encryption  function.  It is based on the Data
       Encryption  Standard  algorithm  with  variations  intended  (among  other
       things) to discourage use of hardware implementations of a key search.

       key is a user's typed password.

       salt  is  a  two-character string chosen from the set [a-zA-Z0-9./].  This 
       string is used to perturb the algorithm in one of 4096 different ways.