YALE UNIVERSITY
DEPARTMENT OF COMPUTER SCIENCE
CPSC 467a: Cryptography and Computer Security

Professor M. J. Fischer

Handout #3

September 27, 2005

Problem Set 2

Due in class on Tuesday, October 4, 2005.

In the problems below, "textbook" refers to Introduction to
Cryptography with Coding Theory: Second Edition by Trappe and
Washington..

Problem 7: Simplified CFB Mode

Textbook, problem 4.9.9.

Problem 8: DES Brute Force Speedup

Textbook, problem 4.9.11.

Problem 9: Birthday Paradox Calculation

Write a computer program to compute p_{n}, the probability that at
least two people in a random collection of n people have the same
birthday. Ignore leap years and assume the probability of a person's
birthday falling on any given day is exactly 1/365, independent of
everyone else in the set. Your program should work for n in the
range [1, 365]. Using your program, find the smallest value of n
for which p_{n} ≥ 1/2 and for which p_{n} ≥ 3/4.

Problem 10: Simplified DES Implementation

Textbook, problem 4.10.1.

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