COT5937Lec2

# COT5937Lec2 - Next we took a look at the substitution...

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Cryptography Lecture Two Overview We started the lecture continuing to talk about the affine cipher. We first showed how to find an inverse of a number a (mod n). Next, we used this information to show how to find the keys to decrypt an affine cipher given valid encryption keys. (We also proved that the affine cipher actually DOES work, when gcd(a,n) = 1. n=number of letters in the alphabet.) We also showed that the equation ax + by = c has integer solutions for x and y, given a, b, and c iff gcd(a,b) | c.
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Unformatted text preview: Next we took a look at the substitution cipher and the Vigenere cipher which are both presented in the text. We will deal with these in more detail when looking at their how to cryptanalyze them. Finally, the Hill cipher was introduced. Inherent in making this work is the idea of inverting a matrix (mod n). For the most part, we went through the process of inverting such a matrix. We also briefly showed how to encrypt data through matrix multiplication, given the key for the Hill cipher....
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## This document was uploaded on 07/14/2011.

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