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Unformatted text preview: time required to break exceeds lifetime of the information D. Caeser Cipher 1. C = E(p,k) = (p+k) mod 26 E. Affine Cipher 1. C = E(p, a, b) = (ap+b) mod 26 No detail about what a's and b's are permissible today. F. Substitution Cipher Substitute any one letter for another! Frequency Analysis can be used to break it. 1. Look for most frequent letters 2. Look for common digrams and trigrams, and other repeated sections of ciphertext. G. Playfair 5x5 grid Fill in key word and double I/J. 1. Repeated plaintext letters in a pair filled with an X or another filler. 2. Same row > each letter to the right in the row. 3. Same column > each letter below 4. letter in the SAME row, and the column of the other letter....
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 Summer '09

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