1. Suppose the DES F function mapped every 32-bit input R, regardless of the value of  the input K, to
a. 32-bit string of ones
b. bitwise complement of R
c. returning R
Hint: Use the following properties of the XOR operation:
1. What function would DES then compute?
2. What would the decryption look like?
(A⊕ B) ⊕ C = A⊕ (B ⊕ C)
A⊕ A = 0
A⊕ 0 = A
A⊕ 1 = bitwise complement of A
where
A,B,C are n-bit strings of bits
0 is an n-bit string of zeros
1 is an n-bit string of one

2. Let plaintext blocks P1, P2, . . ., Pn be encrypted using CBC to produce ciphertext blocks
C1, C2, . . ., Cn. Can encryption be done in parallel? Can decryption?

Do the same question, only use OFB.