The function passwd2des() takes a character string passwd of
arbitrary length and fills a character array key of length 8. The array
key is suitable for use as DES key. It has odd parity set in bit 0 of
each byte. Both other functions described here use this function to turn their
argument passwd into a DES key.
The xencrypt() function takes the ASCII character string secret
given in hex, which must have a length that is a multiple of 16, encrypts it
using the DES key derived from passwd by passwd2des(), and
outputs the result again in secret as a hex string of the same length.
The xdecrypt() function performs the converse operation.