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CAP: Cryptographic Analysis Program Affine Cipher Help Presentation

Learn how to use the Affine Cipher system to encrypt and decrypt messages with ease. Follow the steps provided to select key numbers, encode text, and decipher encrypted messages. Perfect for cryptography enthusiasts.

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CAP: Cryptographic Analysis Program Affine Cipher Help Presentation

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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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