crypt, setkey, encrypt - DES encryption

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

const char *key;

encrypt(block, edflag)
char *block;
int edflag;

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 characters 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. If edflag is 0, the argument is encrypted; if non-zero,
it is decrypted.

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

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