Unformatted text preview: (b) Write the formula used by the Beaufort cipher to decipher the ith ciphertext letter c i . (c) Explain why Kasiski’s method works to ±nd the length t of the key word for Beaufort just as it does for Vigen` ere. (d) Explain why the Index of Coincidence method works to ±nd the length t of the key word for Beaufort just as it does for Vigen` ere. 2. Suppose a Kasiski analysis identi±es these six pairs of repeated sequences in the ciphertext of a Vigen` ere cipher: Location of start of ±rst occurrence 10 21 37 49 58 72 second occurrence 34 65 109 105 162 132 What can you conclude about the length t of the key word used to encrypt the message? Explain your answer. 1...
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 Spring '10
 Wagstaff
 Cryptography, Encryption, Beaufort, Beaufort cipher

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