Week 2

Lecture 2 (01/29/08, Tu): We covered some general terms related to security, such as
various attack models (chosen plaintext/ciphertext). We discussed various classical
ciphers. We covered one-time-pad and how they can be made practical using psuedo-random
number generators (PRGs). We spend some time on the Blum-Blum-Shub (BBS) PRG. More
information about the BBS generator can be found in the handbook (which is linked to
the class web-page).

Lecture 3 (01/31/08, Th): We covered linear feedback shift registers (LFSRs) and showed
a known plaintext attack on it (the attack was based on the linear relationship between
the bits of the keystream). We discussed one way to break the non-linearity (called the
Geffe generator). We discussed Fiestel cipher, which is a general way to build block ciphers.