Sections 4.1, 4.2, and 4.4 for September 20

1. (Difficult) I was very confused about the DES method and the simplified example provided in section 4.2. I think it was mainly the notation and the use of bits that made it confusing for me. I understood some of the simpler steps, such as using the S-boxes and XOR, but it was the process and steps that confused me. Using the Initial Permutation table was clear, but then I did not understand how to use several of the other tables. I understand that R is the last 32-bits of a sequence of 64-bits, but what is the function E(R)?

2. (Reflective) I find it interesting the history of many of the different methods of cryptosystems. It is amazing how something that seems secure 30 years ago can now be relatively easily broken. Also, the fact that DES was used and then replaced shows the importance of continuing to study cryptography and a lot of other subjects. Different methods are meant to be broken eventually and replaced by a better one, and then a another one, and another. There was a psychologist that believed that good theories and ideas have to be falsifiable. That is, that ideas need to have the option to be false, so that better ideas can come about in an effort to proof current ideas false. It is an interesting thing to think about. We come up with pretty good ideas, and then we try to disprove their security so that better ideas will emerge.