Outline for November 6, 2006

Reading: §9.2

  1. Greetings and felicitations!
    1. Quick review for midterm
  2. Classical Cryptography
    1. Polyalphabetic: Vigenère, fi(a) = a + ki mod n
    2. Cryptanalysis: first do index of coincidence to see if it is monoalphabetic or polyalphabetic, then Kasiski method.
    3. Problem: eliminate periodicity of key
  3. Long key generation
    1. Autokey cipher: M = THETREASUREISBURIED; K = HELLOTHETREASUREISB; C = ALPEFXHWNIIIKVLVQWE
    2. Running-key cipher: M = THETREASUREISBURIED; K = THESECONDCIPHERISAN; C = MOILVGOFXTMXZFLZAEQ; 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.)
    3. Perfect secrecy: when the probability of computing the plaintext message is the same whether or not you have the ciphertext
    4. Only cipher with perfect secrecy: one-time pads; C = AZPR; is that DOIT or DONT?
  4. DES
You can also obtain a PDF version of this. Version of November 5, 2006 at 5:54 PM