Outline for October 6, 2021

Reading: text, §10.2
Due: Homework 1, due October 6; Project selection, due Oct 8

  1. Symmetric Cryptography
    1. Monoalphabetic (simple substitution): f(a) = a + k mod n
    2. Example: Caesar (shift) cipher with k = 3, RENAISSANCEUHQDLVVDQFH

  2. Symmetric Cryptography
    1. Polyalphabetic: Vigenère, fi(a) = a + ki mod n
    2. Cryptanalysis: use index of coincidence to see if it is monoalphabetic or polyalphabetic; Kasiski method.
    3. Problem: eliminate periodicity of key
    4. 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?

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Matt Bishop
Office: 2209 Watershed Sciences
Phone: +1 (530) 752-8060
Email: mabishop@ucdavis.edu
ECS 235A, Computer and Information Security
Version of October 6, 2021 at 10:54PM

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