(Known plaintext attack for affine cipher.) Suppose the plaintext starts with if and the corresponding ciphertext is PQ. This means (8, 5) → (15, 16). This gives the simultancous equations 8a + B = 15 (mod 26) 6a +ß = 16 (mod 26) Solve this in modular arithmetic to get the keys a = 17, B = 9.

Database System Concepts
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ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
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Chapter1: Introduction
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(2) (Known plaintext attack for affinc cipher.) Suppose the plaintext starts with if and the
corresponding ciphertext is PQ. This means
(8, 5) → (15, 16).
This gives the simultancous equations
8a + B = 15 (mod 26)
ба + В 3 16 (шod 26)
Solve this in modular arithmetic to get the keys a = 17, ß = 9.
Transcribed Image Text:(2) (Known plaintext attack for affinc cipher.) Suppose the plaintext starts with if and the corresponding ciphertext is PQ. This means (8, 5) → (15, 16). This gives the simultancous equations 8a + B = 15 (mod 26) ба + В 3 16 (шod 26) Solve this in modular arithmetic to get the keys a = 17, ß = 9.
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