Sections 4.5-4.8 for September 22

1. (Difficult) Section 4.5 was pretty difficult to understand. I didn't understand the differences in many of the five modes of operation. I understood the first one, ECB, and the way it is attacked, but the Cipher Feedback (CFB) and Output Feedback (OFB) were confusing, even with the diagrams. I did not fully understand the Meet-in-the-Middle Attack either. I understand that this attack shows that the composition of two keys does not make it any more secure, but the process is not clear to me.

2. (Reflective) I find it interesting the way that DES was broken. I took a seminar on parallel computing, and the use of several computers to break one code makes a lot of sense. Using multiple computers at one time is much more efficient than using one computer. Parallel computing makes many seemingly "impossible" problems possible.

I really like the concept of "interesting" decrypted messages. When I first read that, I was wondering what it meant, but then the explanation explained it. It shows that even though the DES system can be broken by using parallel computing and checking the keys, that a lot of work is being done that is somewhat useless. Many of the keys are simply discarded.