Reading Note on Chapter 3 (Block Ciphers and The Data Encryption Standard)

· Read 3.1 in details

§ What is the difference between stream cipher and block cipher? Which one is more advantageous and why?

§ What are advantages of Feistel Cipher Structure? What are the disadvantages of any arbitrary reversible block cipher?

§ Explain the terms confusion and diffusion.

§ What is substitution?

§ What are parameters of Fiestel network? How does the performance of a Feistel structure vary with variation in these parameters?

§ Read Feistel Decryption Algorithm and understand the calculations well. Make sure that you understand XOR property and how it is used in the algorithm.

· Read section 3.2.

§ Read the general descriptions of DES.

§ Apply the Permutations of Table 3.2 on the 8x8 matrix on page 75 and see what result you get. You may even take any arbitrary 8x8 matrix and test. Remember that the numbers in the permutation tables are positions of each entry.

§ Study Figure 3.5 carefully.

§ Study DES Key schedule calculation carefully.

§ What is Avalanche effect? How does DES exhibit avalanche effect?

· Read section 3.3 well.

§ What are the strengths of DES key? What are its weaknesses?

§ How can cryptanalysis be done on DES by exploiting its characteristics?

§ How can timing attack be used to decipher symmetric ciphers?

· You may skip section 3.4

· Read section 3.5

§ What are design criteria of DES?

§ Why the number of rounds is important?

§ What should be the characteristics of function F in Feistel structure?