2.1-2.2 and 2.4, Due on September 10

Difficult: The most difficult part of today's reading for me was understanding the frequency analysis counting diagram idea in section 2.4. It seemed like they were successful in decoding the message mainly because of "lucky" guessing, or probably more because they were the ones who encoded it. I am still trying to follow the logic in this section. One of the hang ups I have is, what happens when the frequency is wrong? For example, the book mentions entire novels carefully written with no e's, couldn't a secret message be purposely written the same way? This would throw off the frequency analysis. Another example I noticed of frequency analysis being wrong was in our homework (number 3). The most frequently used letter there was t, not e.

Reflective: I was very interested in the use of affine ciphers. In particular, I enjoyed the discussion of using a known plaintext attack to decode them. The text said this could be accomplished with "a bit of luck", but the procedure it outlined seemed to show that you would have to have luck to hit letters that did not help you. As the text says "The...procedure works unless we get a gcd of 13 (or 26)". This seems really specific circumstances to me. I also enjoyed seeing the use of modulus, which has always seemed a mostly useless concept, to make ciphers.