One aspect that I am curious about is the phrase "highly unlinear." The S-boxes of the Rijndael System are repeatedly described this way and I've heard that phrase used in class as well. Does this phrase have a unique meaning or does it just mean what it sounds like? And why do they throw the highly in there? It seems that being linearity is a black and white topic, without any variation or degrees. I find the idea of multiple rounds to complicate a cryptosystem to be a very good idea. It complicates the message greatly while only complicating the algorithm slightly.
Section 5.2.5 on The Key Schedule was the hardest portion of the reading for me to follow. I can catch the bigger picture about what is happening with the different layers but the key schedule was very confusing. I understand that W(i) is a column vector but I don't know what happens when it is transformed with T(W(i-1)) and I don't understand what the r(i) represents. What exactly is the round key?
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