CS327-Cryptography

Nicholas Tamassia

February 27, 2025

CS-327

Cryptography PA

Program Location: /cs/home/stu/tamassno/cs327/cryptography_PA/affine.py

Usage: python affine.py [encrypt | decrypt | decipher] --help

Questions

7.1 Part 1

D(c,a,b)=a^{-1}(c-b)\;\text{mod}\;128

7.1 Part 2

Restrictions on a and b:

0 < a < 128, a and 128 must be coprime, i.e. \text{gcd}(128,a)=1
0 \leq b < 128

7.1 Part 3

Because 128 is coprime with all odd numbers less than itself (1, 3, 5, …, 127), there are 64 possible values for a. There are 128 options for b so there exists an upper limit on valid a, b pairs of 8192.