a) For a bit string S, let S denote the complement, obtained by swapping every 1 for a 0 and every 0 for a 1. Equivalently, S = S O 111...11. Show that, encrypting with DES, if C = Ek(M), then ER(M) = C. Hint: Work through DES step by step, and show that in both cases, the input into the S-boxes is the same (meaning, fortunately, you don't have to look at the S-boxes to solve this problem). b) Explain how the above property can be used to cut the time required for a brute-force attack in half.

a) For a bit string S, let S denote the complement, obtained by swapping every 1 for a 0 and every 0 for a 1. Equivalently, S = S O 111...11. Show that, encrypting with DES, if C = Ek(M), then ER(M) = C. Hint: Work through DES step by step, and show that in both cases, the input into the S-boxes is the same (meaning, fortunately, you don't have to look at the S-boxes to solve this problem). b) Explain how the above property can be used to cut the time required for a brute-force attack in half.

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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