DES is the old Data Encryption Standard, specified by NIST. It
uses a block size of 64 bits (8 octets), and a key size of 56
bits. However, the key bits are distributed over 8 octets, where
the least significant bit of each octet is used for parity. A
common way to use DES is to generate 8 random octets in some way,
then set the least significant bit of each octet to get odd
parity, and initialize DES with the resulting key.
The key size of DES is so small that keys can be found by brute
force, using specialized hardware or lots of ordinary work
stations in parallel. One shouldn't be using plain DES at all
today, if one uses DES at all one should be using DES3 or "triple
DES".
DES also has some weak keys.
Crypto.CAST