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Unformatted text preview: Math 187 Prof. Garsia (typed by Alex Brik) 04-06-2009 SAMPLE QUIZ 1 solution. 1. Let 1,2,3,...,n be an indexing of ciphertext letters. A Vigenere cipher with a 2 letter key will encryot every letter with index k & 1(mod 2) using &rst letter of the key, and will encrypt every letter with index k & 0(mod 2) using the second letter of the key as follows: for every letter of the alphabet let n ( ) be its index from to 25 so that n ( A ) = 0 , n ( B ) = 1 , n ( C ) = 2 ;:::;n ( Z ) = 25 . For an integer k from to 25 ket alpha ( k ) be the letter of the alphabet so that n ( ) = k . That is alpha (0) = A , alpha (1) = B ;:::;alpha (25) = Z . Let & 1 , & 2 be two letter key, where & 1 , & 2 are letters of the alphabet. Then for the letters with index k & 1(mod 2) the encryption will map: A ! & 1 , B ! alpha ( n ( & 1 ) + 1 (mod 26)) , C ! alpha ( n ( & 1 ) + 2 (mod 26)) , ... Z ! alpha ( n ( & 1 ) + 25 (mod 26)) ....
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