(Chapter 3: Block Ciphers and The Data Encryption Standard)
Total Marks: 30
Due Date: February 2nd , 2010, by Midnight EST
Answer any two. If you can solve all three, you will get 5 points extra.
1. Why is it important to study Fiestel structure? What is the difference between a block cipher and a stream cipher? 5+5
2. Suppose the DES F function mapped every 32 bit input R, regardless of the input K, to
a. 32-bit string of 1s
b. Bitwise compliment of R.
What function would DES compute in these cases? What would the decryption look like?
(This problem is from the book, page 92, question # 3.7. The book provides a hint. You may want to look at that.)
5+5+5+5