solution 1

Introduction to Modern Cryptography: Principles and Protocols (Chapman & Hall/CRC Cryptography and Network Security Series)

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ICS 201: Cryptography and Communication Security 10/19/2007 Solutions to homework 1 Problem 2.2 If encryption is secure then by Definition 2.1 this condition implies that Pr [ M = m ] = Pr [ M = m ] for all m,m in the message space, which is obviously not true if M is sampled from any distribution over the message space. Problem 2.3 After throwing out the key k = 0 l the OTP encryption is no longer perfectly secure because then the key-space has one fewer element than the message space. A good example is that for any c { , 1 } l the message m = c is impossible, because O l negationslash K . But any other message is possible, which violates for example the condition in lemma 2.3, which says that encryption is perfectly secure only if for all c,m ,m 1 the probability that m encrypts to c (over keys) is the same as the probability that m 1 encrypts to c (over keys). Problem 2.4(b) Since the substitution cipher has key-space K of size 26!, it can provide perfect secrecy only if the message space M has at most 26! elements too. Lethas at most 26!...
View Full Document

This homework help was uploaded on 01/30/2008 for the course CS 201 taught by Professor Jarecki during the Fall '07 term at UC Irvine.

Page1 / 2

solution 1 - ICS 201: Cryptography and Communication...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online