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 pn, 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 pn ≥ 1/2 and for which pn ≥ 3/4.
Problem 10: Simplified DES Implementation
Textbook, problem 4.10.1.
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