Authentication/Key Distribution(2+4+2+2) Consider the following protocol for Authentication/Key Distribution: (X and Y are two nodes, A is a CA/KDC, N_1 and N_2 are random numbers, and E_x means encrypted with the secret key of X.) 1. X rightarrow A: X, Y, N_1 2. A rightarrow X: E_x (N_1, X, Y, K, E_y (K, X)) 3. X rightarrow Y: E_y(K, X) 4. Y rightarrow X: E_k(N_2) 5. X rightarrow Y: E_K(N_2 - 1) What is purpose of N_1 in message 2? Show that if an attacker were to break an old K, he/she can impersonate user X to user Y. How to solve this problem? What is the purpose of Steps 4 and 5