Question

Question 1 10 pts Suppose the DES encryption is denoted by C EK P], while the DES decryption is denoted by P DK C where C and P refer to the ciphertext and the plaintext, respectively. Which of the following expression denotes the encryption and decryption of the 3DES algorithm? (K1, K2, and K3 are secret keys).

Answer 1

Answer: D

3DES is also known as triple DES because here we will do DES 3 times. Here we will use 3 keys. Let us consider K1, K2, K3 are 3 Keys.[

C : First Encrypt with K1, Decrypt with K2 and then Encrypt with K3.

therefore, C= E_K3[D_K2[E_K1[P]]]

D : Here, first Decrypt with K3, Encrypt with K2 and then Decrypt with K1.

therefore, P= D_K1[E_K2[D_K3[C]]].

Answer 2

Solution:

The expression which denotes the encryption and decryption of 3DS Algorithm :

d)

C = E_K3[D_K2[E_K1[P]]] and
P = D_K1[E_K2[D_K3[C]]]