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CAP Cryptographic Analysis Program

CAP Cryptographic Analysis Program. Affine Cipher Help Presentation. Press Enter or click on your mouse button to continue. The Affine Cipher System. The affine cipher is another version of a substitution cipher Each letter is assigned a number A = 0, B = 1, . . ., Z = 25

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CAP Cryptographic Analysis Program

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  1. CAPCryptographic Analysis Program Affine Cipher Help Presentation Press Enter or click on your mouse button to continue

  2. The Affine Cipher System • The affine cipher is another version of a substitution cipher • Each letter is assigned a number • A = 0, B = 1, . . ., Z = 25 • Two numbers are selected (a, b) between 0 and 25 such that the gcd(a,26) = 1 • Let p and c represent letters (p,c are numbers between 0 and 26) where p is a plaintext letter and c is a ciphertext letter then: c = ap + b mod 26 p = a-1(c - b) mod 26

  3. Affine Example • Select the key (a,b) = (7, 3) • gcd(7,26) = 1 • 7-1 mod 26 = 15 (since 7 x 15 = 105 and 105 mod 26 = 1) The general encipher/decipher equations are: c = 7p + 3 mod 26 “hot” is 7 14 19 c(h) = 7*7 + 3 mod 26 = 52 mod 26 = 0 = a c(o) = 7*14 + 3 mod 26 = 98 mod 26 = 23 = x c(t) = 7*19 + 3 mod 26 = 133 mod 26 = 6 = g

  4. Affine Cipher in CAP • Select the Affine option under the cipher menu . . . Error message if you fail to select the correct key numbers This will set up your key Enter the two numbers

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