4.1-4.2,4.4

1. I had a hard time following the algorithm, or at least appreciating what the algorithm was doing. It'd be nice to go over the proof again, too.

2. The DES algorithm seems like a convoluted process. The fact that many suspected there was a backdoor suggests to me that some security through obscurity is employed with this algorithm. The book said that the initial permutation was probably to optimize it for the hardware of the time. This, plus the linear feedback cipher, makes me wonder how much an algorithm's security is compromised in the name of speed.

This slideshow article came up today. It's not super interesting, but it is topical: pictorial representation of the past six decades of research and development in encryption.