= Block Ciphers and DES =

== S-DES ==

The plaintext is processed by S-DES in two rounds where each round encrypts half of the plain text after it has been permuted. The key for each round is generated by a seperate process and both can be seen in attachment:s-des-map.pdf.

S-DES operates on 8-bit blocks and uses a 10-bit key. DES uses 64-bit blocks and a 56-bit key.

== Block Cipher Principles ==

Block ciphers use a fixed length block of plaintext and produce an equal sized block of cipher text.