Section 4.5

The most interesting parts here were definitely the feedback methods. The way the output from the encryption would be XORed or shifted along with the use of the differing keys is a nice way to solve the problem of transmitting data of varying sizes. Even more interesting is the fact that the mode of operation plays a part in the cryptanalysis of DES and things beyond the algorithm can cause it to perform better or worse. I also wonder what the affects would be if the various modes were used together. Coming up with a cryptanalysis of the counter mode strikes me as a difficult task especially compared to the codebooks, once again its interesting how much of a role the mode of operation for DES plays in breaking it.