NAME

crypt, encrypt − a one way hashing encryption algorithm

SYNOPSIS

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

encrypt(block)
char *block;

DESCRIPTION

Crypt is the password encryption routine.  It is based on a one way hashing encryption algorithm with variations intended (among other things) to frustrate 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 hashing 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.  The first two characters are the salt itself. 

There is a character array of length 64 containing only the characters with numerical value 0 and 1.  When 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 by crypt. 

The encrypt entry provides (rather primitive) access to the actual hashing algorithm.  The argument to the encrypt entry is a character array of length 64 containing only the characters with numerical value of 0 and 1.  The argument array is modified in place to a similar array representing the bits of the argument after having been subjected to the hashing algorithm using the key set by crypt. 

SEE ALSO

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

RESTRICTIONS

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