The most difficult part of this reading for me was understanding the affine functions. I think my knowledge of multiplicative inverses in modular arithmetic is a little rusty and I couldn't recall why 1/9 is the multiplicative inverse of 3 in mod 26. I understood most of the other aspects of affine functions but that one little part about inverses and the need for gcd (alpha, 26) =1 eluded me.
The frequency analysis and its accompanying parts was the most interesting. Looking at the frequency table on page 25 showed me how close some letter frequencies are (for example, h was .061 and r was .060). That type of analysis seems to be only relevant for finding e- the dominant favorite letter- and maybe t and a. I enjoyed reading about the two-letter frequencies and the patterns in the English language that help with the analysis. It made me realize how difficult this could be if a message was intercepted and the language was unknown. The substitution cipher seems much easier to crack if the language is known.
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