Exam1RevSols

Exam1RevSols - Crypto Exam #1 Review Solutions 1) Using an...

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Crypto Exam #1 Review Solutions 1) Using an affine cipher with the encryption keys a = 9, b = 5, encrypt the plaintext "KNIGHTS" f(10) = 9(10) + 5 = 95 = 17 mod 26 ( R ) f(13) = 9(13) + 5 = 122 = 18 mod 26 ( S ) f(8) = 9(8) + 5 = 77 = 25 mod 26 ( Z ) f(6) = 9(6) + 5 = 59 = 7 mod 26 ( H ) f(7) = 9(7) + 5 = 68 = 16 mod 26 ( Q ) f(19) = 9(19) + 5 = 176 = 20 mod 26 ( U ) f(18) = 9(18) + 5 = 167 = 11 mod 26 ( L ) Answer: RSZHQUL 2) If the encryption keys for the affine cipher are a = 9 and b = 5, what are the corresponding decryption keys? x = 9y + 5 mod 26 9y = (x – 5) mod 26 3(9y) = 3(x – 5) mod 26 y = (3x – 15) mod 26 y = (3x + 11) mod 26 3) Consider using the affine cipher on an alphabet of size 20. How many possible keys would there be? The value of a can be either 1, 3, 7, 9, 11, 13, 17 or 19. The value of b can be any integer from 0 to 19. Thus, there are a total of 8 x 20 = 160 possible keys. 4) Find 36

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This note was uploaded on 07/13/2011 for the course CIS 3362 taught by Professor Staff during the Fall '08 term at University of Central Florida.

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Exam1RevSols - Crypto Exam #1 Review Solutions 1) Using an...

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