Outline for February 22, 2006
Reading: text, §9.2
- Greetings and felicitations!
- Puzzle of the day
- Classical Cryptography
- Polyalphabetic: Vigenère,
= a +
- Cryptanalysis: first do index of coincidence to
see if it’s monoalphabetic or polyalphabetic, then Kasiski
- Problem: eliminate periodicity of key
- Long key generation
- 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.)
- Perfect secrecy: when the probability of computing
the plaintext message is the same whether or not you have
- Only cipher with perfect secrecy: one-time pads;
C = AZPR; is that DOIT or DONT?
Version of February 23, 2006 at 8:55 PM
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