550.371/650.471 Cryptology, Exam 1, Spring 2015
Problem 1: (10 points) Diagram one round of DES, diagram the reversal-round for this round
of DES, and show algebraically that the reversal-round indeed undoes the round.
Problem 2: (10 points) Suppose a b >
Solutions for Homework 4, 550.371 Cryptology, Spring 2015
Problem 1: If m and n are integers not both zero, we dene their least common multiple lcm(m, n)
to be the smallest positive integer z such that m|z and n|z. Describe how to eciently compute
lcm(m,
Homework 3 solutions, 550.371 Cryptology, Spring 2015
MATLAB code for Problems 1 and 2 are in an accompanying le.
Problem 3: [Trappe and Washington textbook, Section 3.13 on page 104, Problem 4]
a) Use the Euclidean Algorithm to compute gcd(30030, 257).
S