Outline for April 14, 1997

1. Greetings and Felicitations
2. Simple substitution ciphers
   1. Do Caesar cipher
   2. Go through how to break it
   3. Present Vigenère tableau
   4. Discuss breaking it (Kasiski method). Note index of coincidence is probability 2 letters chosen at random from ciphertext are alike
   5. Generalize to very long keys and show running key and autokey
   6. Go through rotor systems (Enigma)
   7. Go through one-time pads
3. Polygram substitution cipher: Playfair
   1. Key is 5 by 5 grid
   2. If m₁, m₂ in same row, c₁, c₂ are to immediate right of m₁, m₂ respectively
   3. If m₁, m₂ in same column, c₁, c₂ are below m₁, m₂
   4. If m₁ = m₂, insert null in text
   5. if m₁, m₂ in different rows and columns, c₁, c₂ form rectangle with c₁ in m₁'s row and c₂ in m₂'s row
   6. if odd number of characters in message, append null.