## CSci 4509 Cryptographic Protocols -- Problem set 2.

### Problem 1: encrypting with SPN (7 points)

Consider the SPN in example 3.1 (the one that we considered in class). Suppose the key for the SPN is changed to
``````
K = 1011 0101 1100 0101 1001 1110 1011 0010
``````
What would be the encryption of the plaintext
``````
x = 0010 0110 1011 0111
``````
using this key? Please show ALL your intermediate results (i.e. w, u, and v at each level). You may compute the encryption by hand or write an implementation.

### Problem 2: decrypting with SPN (4 points)

Exercise 3.1 p. 113.

### Problem 3: linear cryptanalysis of SPN (question (a) 4 points, the rest extra credit)

Exercise 3.14 p. 115 questions a, b, and c only.

### Problem 4: cryptanalysis of DES (8 points)

Exercise 3.10 p. 115. Important modification: you may compute the bias of this variable for any 2 DES S-boxes if you are working by yourself, and for any 4 DES S-boxes if you are working as a team of two. Please submit all the intermediate results.

### Problem 5: modes of operation of block ciphers (4 points)

Exercise 3.7 p. 114.

### Problem 6: AES (8 points)

Exercise 3.5: construct the first 4 keys only.
Use the palintext given in exercise 3.6 and compute only the beginning of encryption of this text with AES: perform AddRoundKey, SubBytes, and ShiftRows (since we didn't talk about the exact algorithm for MixColumns, you don't need to perform that step).
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