Lecture 13 Outline
Reading: §10.2–10.2.4, F
Due: Homework 3, due on May 9, 2018 at 11:59pm; Lab 2, due on May 7, 2018 at 11:59pm
- Symmetric Cryptography
- Polyalphabetic: Vigenère, f_{i}(a) = a + k_{i}
- Cryptanalysis: first do index of coincidence to see if it is monoalphabetic or polyalphabetic, then Kasiski method.
- Problem: eliminate periodicity of key
- Long key generation
- Autokey cipher: key is keyword followed by plaintext or cipher text
- Running-key cipher: key is simply text; wedge is that (plaintext, key) letter pairs are not random (T/T, H/H, E/E, T/S, R/E, A/O, S/N, etc.)
- Perfect secrecy: when the probability of computing the plaintext message is the same whether or not you have the ciphertext; only cipher with perfect secrecy: one-time pads; C = AZPR; is that DOIT or DONT?
- Product ciphers: DES