(Interesting) I was most interested in section 4.4 when they brought up the topic of whether DES was a group. When we designed our cryptosystem in class I assumed working with groups (such as mods under addition or multiplication) would be the best way to go because they are closed operations. Because they are closed under addition or multiplication, it is easy to assure your outputs will be in the correct range of acceptable values in order to encrypt a message. However, I had not considered the possibility of the security weaknesses of groups. When we constructed our own cryptosystem, I had considered using two keys in order to encrypt our messages. After thinking about group theory, I realized that using two keys would be equivalent to using only one key. This means that rather than adding security, this type of encryption would only be redundant, and waste more time and resources for encryption.
(Difficult) The most difficult part of the reading for me was the function used in DES. Although the flowchart on page 126 was well-organized, I did not completely understand what was going on in the DES function. I understand how the expander function and XORing works, but the S-boxes were where I was lost.
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