For affine cipher, the key is a pair (a,b) for a,b<26. The encryption algorithm is E(x)=(ax+b) mod 26. And the decryption algorithm is D(y)=a¹(y-b) mod 26. Note that we map A, B, C, D, ... to numbers 0, 1, 2, 3, ... respectively. Assume that K=(7,3), then E(x)=(7x+3) mod 26, and 7-1-15. Thus D(y)=15(y-3) mod 26. 1. For the key K=(7,3), computer the cipher text for "GOLUNCH" is (please use all capital letters) 2. For the key K=(7,3), try to decrypt the cipher text "YHQQFPGHJF" is (please use all capital letters)

For affine cipher, the key is a pair (a,b) for a,b<26. The encryption algorithm is E(x)=(ax+b) mod 26. And the decryption algorithm is D(y)=a¹(y-b) mod 26. Note that we map A, B, C, D, ... to numbers 0, 1, 2, 3, ... respectively. Assume that K=(7,3), then E(x)=(7x+3) mod 26, and 7-1-15. Thus D(y)=15(y-3) mod 26. 1. For the key K=(7,3), computer the cipher text for "GOLUNCH" is (please use all capital letters) 2. For the key K=(7,3), try to decrypt the cipher text "YHQQFPGHJF" is (please use all capital letters)

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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Suppose that Alice and Bob communicate using ElGamal cipher and f (p. 9. Z) is common public values. Bob generates his private key d ER Z and then computes the corresponding and public public key y=g" (mod p). To save time, Bob uses the same number r each time he encrypts a plaintext message m (ie., r is a fixed nonce of Bob, and it is not randomly generated each time encryption is performed). Assume that Alice compute the ciphertext for the message m as (cc) = (g mod p, mxy mod p). and for the message m as (1,2)=(g" mod p, xy' mod p). Show how an adversary who possesses a plaintext-ciphertext pair (m. (c.ca)) can decrypt (1, 2) without knowing the private key d of Bob.
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Question 1 Study the scenario and complete the question(s) that follow: Ceasar Cipher The Caesar Cipher technique is one of the earliest and simplest method of encryption technique. It's simply a type of substitution cipher, i.e., each letter of a given text is replaced by a letter some fixed number of positions down the alphabet. For example with a shift of 1, A would be replaced by B, B would become C, and so on. The method is apparently named after Julius Caesar, who apparently used it to communicate with his officials. 1.1 Write a Ceasar cipher algorithm in such a way that a character D is changed to N. Derive the encryption of the other characters accordingly. 1.2 Based on your algorithm, what will be the encrypted code of the message “my mother is not home". End of Question 1