Unformatted text preview: where the addition is taken “mod 26” (for the key k, we map x to (x+k)%26). • This is easy to encode and decode by hand, but not very secure. Even if your enemy does not know the key, they can quickly determine which of the 26 possible keys you are using. And even an arbitrary mapping of letters to letters is subject to frequency analysis the most common ciphertext letter is likely to be the translation of E, the most common pair is TH, and so forth....
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 Fall '11
 barrington
 Cryptography, Data Structures, Julius Caesar, Substitution cipher, substitution ciphers, common ciphertext letter

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