Lecture 2. Classical cryptosystems 2
In this lecture we continue the overview of the classical cryptosystems.
Hill cipher
Lester S. Hill proposes a polygraphic substitution cipher based on linear algebra. It was the
rst polygraphic cipher in which it was

Lecture 1. Classical cryptosystems 1
Introduction
The modern cryptography can be split in two large areas private key cryptography and public
key cryptography, also called symmetric and asymmetric cryptography, respectively. The rst
lectures of this cours

Lecture 3. Elementary cryptoanalysis
This lecture is devoted to the analysis of the classical cryptosystems described in the previous
two lectures. Note that many ideas from this lecture can be useful for understanding attacks of
modern ciphers as well.
L

Lecture 5. Block ciphers (DES, AES) 2
Generating the subkeys in DES
Let K be a 64-bit key. As we know, the eective length is 56 due to the fact that the bits
in positions 8,16,.,64 are parity check bits1 . The 16 subkeys are generated in the following
way

Lecture 4. Block ciphers (DES, AES) 1
Introduction
A block cipher is a symmetric key cipher operating on xed-length groups of bits, called blocks,
with an unvarying transformation. A block cipher encryption algorithm might take (for example)
a 128-bit blo