CSCI-6960H08 Cryptography and Network Security
Modified: Thu, Jan 22, 2004

Homework #1 Due February 7, 2005

Q1 (Stallings Prob 8.3(3rd edition) 7.6 (2nd edition)
Using Fermat's theorem, find 3^201 mod 11

Q2 (Stallings Prob 4.9(3rd ed) 7.9(2nd ed))
Determine x and y: x = gcd(24140, 16762)
and y = gcd(4655,12075)

Q3
Do problem 4.11(3rd ed) or 7.11(2nd ed) in Stallings and evaluate Stein's algorithm
versus Euclid's algorithm (peek at Problem 4.12(3rd ed) or 7.12(2nd ed).

Q4
For a = 0,1,2,3, ..., 15, 16 find the corresponding additive
and multiplicative inverses modulo 17

Q5 (Stallings Prob 4.13(3rd ed)
Using the extended Euclid's algorithm, find the multiplicative inverse of
(a) 1234 mod 4321 (b) 24140 mod 40902 and (c) 550 mod 1769

Q6
If you were given a page of cipher text, what clues could you
look for that would suggest that you have a
a) monoalphabetic substitution cipher
b) homophonic substitution cipher
c) transposition cipher
d) polyalphabetic cipher
e) one-time pad cipher



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