(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.

(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

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Question

(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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