Review due on October 1

• Which topics and ideas do you think are the most important out of those we have studied?
• I think probably types of attacks, gcd, euclidean algorithm, congruences, finite fields, modes of operation.
• What kinds of questions do you expect to see on the exam?
• Maybe some gcd, euclidean algorithm, and congruences questions. I have no idea what to expect.
• What do you need to work on understanding better before the exam?
• I haven't been able to even review yet because I have been doing the homework assignment, so I don't know what I need work on. 

5.1-5.4 due on September 29

1. I had some difficulty with the key schedule. I didn't understand the whole process of how the key was selected from the original key. I also had some trouble following the decryption; especially the part about why the MC step was not used on the last round of the encryption process.

2. I found it interesting that the other four algorithm methods where secure and could have future possible use. What was the criteria for selection? Why was the Rijndael picked? I also found interesting how the S-box construction was carefully chosen to maximized bit diffusion and open so to avoid the mystery that was common with DES.

Course Feedback due on September 26

• How long have you spent on the homework assignments? Did lecture and the reading prepare you for them?
• I have probably spent about 4-6 hours, I think. I think the lectures and the reading were good preparations to the homework. I think the homework also helped clarify things e.g. the LFSR sequence. 
• What has contributed most to your learning in this class thus far?
• I think lectures have been the most beneficial. I feel the book sometimes is a bit confusing and doesn't use good examples. During lectures, my classmates asks questions in which the answers help me understand as well. 
• What do you think would help you learn more effectively or make the class better for you?
• I have thought it would be nice to do a small scale real encryption, decryption and break, though it would seem not plausible to do a decent size plaintext. Seeing the actual process helps me understand. In the book the examples are still quite abstract, and I don't quite follow the process as well. 

3.11 due on September 24

1. I did pretty well understanding until 3.11.3 the LFSR Sequences, no comprende! I am still trying wot work out normal LFSR Sequences. I think I am getting hung up on the notation with the original and now they throw in all this other matrix notation with P(X) stuff, and I can't keep it straight.

2. I thought the addition and multiplication operations of GF(2^8) really interesting. It reminded me of linear algebra taking the coefficients and then XOR them. The idea of modding polynomials is a bit tripping but cool as well.

Sorry this is late. I started this post Wed night and ran out of time, so I saved the draft meaning to come back and finish it later. Since I had went through the action of blogger, my mind kind of checked it off, and I forgot that it needed to be finished.
Also now after doing the homework, I have a better understand how the LFSR works, so 1 is really not so relevant now.

4.5-4.8 due on September 22

1. I have difficulty seeing how errors are generated in the encryption process, for this reason, I have some trouble seeing the difference in the ability of the OFB to be better at error correction than the other modes. To me it seems as though if you program a computer to do something it does it exactly as it was told, so if there were errors, than the encryption prgram needs to be modified. I also had b it of trouble following the password security sections. I think my brain was shot after trying to follow the modes of operation. I think an example would be nice.
2. I found the section about breaking DES interesting, especially that even though it was known that DES was weak and vulnerable, it was still about for over 10 years. It is amazing to see the the difference in technology from when Rocke Verser broke the DES in '97 to the 39 days it took in '98.

4.1,4.2, and 4.4 due on September 20

1. I was lost most of the reading. I think what throws me off the worse it the S-boxes. I just can't quite figure out how they are used. They send in 4 bits, but how do they chose they out put. The example wasn't clear to me how that was done.

2. Cryptography uses a lot of different areas of mathematics. When I was reading section 4.4 DES Is Not a Group. I had to pause and recall what a group was from Math 371. I am going to have to pull out my abstract algebra book and review the properties of a group.

2.9-2.11 due on September 19

1. Ok the LFSR Sequence ... What is going on? I didn't follow ... well pretty much the whole section, so hopefully we will cover it in class.

2.  I thought the one-time pad interesting, but what struck me most interesting was the section about generating truly random bits. Having some experience using random generator, I have wondered how they worked. I now know how and that they were really not random but pseudo-random.

3.8 and 2.5-2.8 due on September 14

1. I had some difficulty understand the process of encrypting and decrypting the playfair cipher. It seemed like it was  suppose to be put in a matrix but the author didn't chose not to for an explanation. The fraction inverse of (mod n) is still a foreign idea to wrap my brain around.

2. I thought the block ciphers and the use of matrices in cryptography interesting. It seems like linear algebra is used every where in all sorts of places in mathematics, yet there is only one undergraduate course offered. Maybe there should be more linear algebra courses.

2.3 due on September 13

1. I think the most difficult part of understanding was the description of finding the key when the author began on vector Ao, Ai, Aj, etc. At the end, I caught the main jest of it and the probabilities, but it is still hazy.
2. I think the Vigenere Cipher is way cool and how it takes care of the frequency analysis of the letters. Even more cool is the methods for breaking it, even though they are not completely understood. Also the book with no e's is pretty interesting.

2.1-2., 2.4 due on September 10

1. I think the hard thing for me to follow was how they described breaking the affine cipher with ciphertext only. It appeared that it was just a brute force, but then where did the 20 character ciphertext come in from?
2. I found it interesting how modulo was used to describe shift ciphers and affine ciphers. I never have thought of a shift cipher as mod 26, but it sure works good to describe it. I liked how the book described the ways to break it the ciphers using ciphertext, known plaintext, chosen plaintext, and chosen cipher text. It seemed like they were both pretty easy to break.

Guest Lecturer, due on September 10

1. The thing most difficult for me to understand was the last bit she said about the general's wife and the problem with the their encryption system. I think it was just a problem because she was out of time and had to go over it quicker than expected.

2. I found it interesting how the leaders protected the identity of people that were friends of the church, as well has communicating in code for political correspondence. It makes sense with the persecution going on to keep such things hidden. It would be real easy for friends to become enemies after receiving persecution.

3.2-3.3, due on September 3

1. I found the last page and a half difficult to wrap my brain around. The first concept is the solutions to ax congruent to b mod n when the gcd(a,n) is not equal to 1. I think it is the relationship between the x is congruent to c mod m as a solution to ax congruent to b mod n. I just don't see how they relate.
The second concept is working with fractions. I can see the benefit when working with large numbers, but seems like a lot more work in the because you would have to know the multiplicative inverse or all the denominators one could divide by for the modulo.

2. Though the operations with congruences are somewhat difficult to get a wrap around, I find it the most interesting.  Congruences are now more than just an interesting fact using remainders. It will be interesting to see how these are applied.