Chapters 5.1-5.4 for lecture 30 September

1. The most difficult part of the section was bout how to reverse MC and then ARK by making some IMC and InvAddRoundKey. I wasn't really sure why this worked.

2. Having seen something like DES previously, understanding AES was definitely easier. It was nice to see a clear reason for why some of the things were derived, like the S-box. This is such a complicated, secure system that I wonder how someone would come up with it!

Post for lecture on 28 September

1. So far the assignments have taken me about as long as they should for a BYU class. The lecture and the reading have been very helpful in answering the problems.
2. The Jeremiah project was a little weird. On the other hand I have enjoyed learning about how to break weak ciphers. The best contribution to my learning is examples and working out the problems myself.
3. The most difficult thing so far has been the DES, which is getting more understandable, so that would be what I should spend more time studying before the test.

Chapter 4.1,4.2,4.4 for lecture 21 September

1. The way to encrypt using DES was difficult to understand. It seems like something that I will need to work out a few times before I will really know how to use it and see how it works. Section 4.1 was helpful for understanding 4.4.

2. This has definitely been the most complicated chapter of the course so far. However a secure cryptosystem must not be easy to break, so it seems likely that further cryptosystems will be more complicated than the ones discussed in chapter 2.

2.9-2.11 For lecture 18 September

1. The algorithms for generating random numbers were a bit tricky. Some of the terminology was unfamiliar and took some time to reread to get the idea.

2. It was interesting to see an application for solving recurrence equations. I solved a few of them over the summer, so it was fun to see that there was a useful application to it, rather than simply solving the problem for fun.

Chapters 3.8, 2.5-2.8 for lecture on 16 Sept

1. The difficult part of this passage was about how to crack the playfair and ADGFX ciphers from the plaintext only. It did not seem like there was a straightforward algorithm but took some educated guesses.

2. The block cipher was very interesting. I had seen it previously. It was fun to see that it could be very vulnerable under the attacks of known or chosen plaintext.

Chapter 2.3 for lecture on 14 Sept

1. The most difficult part of this chapter was understanding why the method for finding the key length works. The explanation was a little unclear at first. However after reading it the section on how to find the key was easy to understand.

2. This cipher seemed more complex than the previous ciphers and it is fun to be able to crack a cipher that is more complex than just a substitution cipher. I also wonder how you might crack a modified Vigniere cipher if you were to change each letter with an affine cipher rather than just a substitution cipher.

Chapters 2.1, 2.2, 2.4 for lecture on 11 September

1. The hardest part was decrypting the affine cipher. It mostly involved recalling what we read in the previous chapter about solving congruences, so I needed to review it to understand it.

2. It was interesting to see some more hints at solving substitution ciphers besides a character count, such as looking at pairs of letters and looking at general trends in English.

Codes in Mormon History

1. The most difficult part was keeping track of who was who. There were a lot of people that did different things, so it took some work to keep it straight.

2. It was interesting to learn that the heading in the Doctrine and Covenants contained an error. I remember reading it but being unable to find the unusual names. It was also interesting to see that codes were necessary for secure communication between Latter-day Saints between Utah and Washington DC.

Section 3.2 and 3.3 Due 4 September

1. The most difficult parts were the extended Euclidian algorithm and a bit about fractions. The algorithm wasn't clear at first, but writing it out on paper helped. The fractions are just different from what I've seen before so they were new and just took some extra time.

2. It was interesting to see how the extended Euclidian algorithm would help solve congruences mod n. At first it seemed like a fun trick, but it was nice to see that there was a useful application to it.

1.1-1.2 and 3.1 due Sept 2

1. What makes public key encryption computationally more difficult than a symmetric key?
2. This section talked about the goals of a cryptographer, and the tactics one could use to find a key. It also explains some elementary number theory that will be important to encoding.