Week 1, Thursday, 2.1-2.4 Rough Draft

7. The most difficult material was understanding how to break the Vigenere Cipher. I understood exactly how the encoded the plaintext but got lost trying to understand the second method used to find the key. I think an example using the second method would clear my confusion up. Examples I've learned are a great tool for learning cryptography. First off, the first chapter and the first four sections of chapter 2 were awesome! I did not fathom how many ways there are to encrypt plaintext and that it went back to julius ceasar. The T.A. was great! And the initial part of chapter 2 went by quickly. It is interesting to note that Julius Ceasar, with such important messages, didn't pick a more compiclicated encryption algorithum. Second, I completely understand what mod 26 is thanks to Pic 10a,b,c and it is interesting to note that you must make sure all numbers in the code are between 0 and 25, and can be done by mod, a cool trick. In addition, it is interesting how we have extended the definition of inverse, when introducing mod. With respect to the Affine Cipher the multiplicative inverse for 9 (mod 26) is 3. I really like how the book introduces the topic and the order that it is in. For example, as I was reading the Affine Cipher I questioned its validity, what if there was more than 1 input that gave the same output. The book went on to describe how to assure one-to-one, which can be shown if and only if gcd(a, 26)=1. Moreover, I find that understanding how to break the code using different techniques and thought processes is interesting. It is sometimes amazing how complicated these codes can seem, yet how easy, if in the right mind-set, one can break them.