A natural question is whether we can use a nonce and public key cryptography to solve the end-point authentication problem in Section 8.4. Consider the following natural protocol: (1) Alice sends the message I am A1 ice” to Bob. (2) Bob chooses a nonce, R. and sends it to Alice. (3) Alice uses her private key to encrypt the nonce and sends the resulting value to Bob. (4) Bob applies Alice’s public key to the received message. Thus, Bob computes R and authenticates Alice.

a. Diagram this protocol, using the notation for public and private keys employed in the textbook.

b. Suppose that certificates are not used. Describe how Trudy can become a “woman–in–the–middle” by intercepting Alice’s messages and then pretending to be Alice to oh.