bsd man page for crypt

CRYPT(3)						     Library Functions Manual							  CRYPT(3)

NAME
       crypt, setkey, encrypt - DES encryption

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

       setkey(key)
       char *key;

       encrypt(block, edflag)
       char *block;

DESCRIPTION
       Crypt  is  the password encryption routine.  It is based on the NBS Data Encryption Standard, with variations intended (among other things)
       to frustrate use of hardware implementations of the DES for key search.

       The first argument to crypt is normally a user's typed password.  The second is a 2-character string chosen  from  the  set  [a-zA-Z0-9./].
       The  salt string is used to perturb the DES algorithm in one of 4096 different ways, after which the password is used as the key to encrypt
       repeatedly a constant string.  The returned value points to the encrypted password, in the same alphabet as the salt.  The first two  char-
       acters are the salt itself.

       The  other entries provide (rather primitive) access to the actual DES algorithm.  The argument of setkey is a character array of length 64
       containing only the characters with numerical value 0 and 1.  If this string is divided into groups of 8, the low-order bit in  each  group
       is ignored, leading to a 56-bit key which is set into the machine.

       The  argument  to  the  encrypt entry is likewise a character array of length 64 containing 0's and 1's.  The argument array is modified in
       place to a similar array representing the bits of the argument after having been subjected to the  DES  algorithm  using  the  key  set	by
       setkey.	The edflag flag is ignored; the argument can only be encrypted.

SEE ALSO
       passwd(1), passwd(5), login(1), getpass(3)

BUGS
       The return value points to static data whose content is overwritten by each call.

7th Edition							  August 12, 1986							  CRYPT(3)