1. Suppose Alice wants to communicate with Bob using symmetric key cryptography using a session key K S . In Section 8.2, we learned how public-key cryptography can be used to distribute the session...

1. Suppose Alice wants to communicate with Bob using symmetric key cryptography using a session key
K_S
. In Section 8.2, we learned how public-key cryptography can be used to distribute the session key from Alice to Bob. In this problem, we explore how the session key can be distributed—without public key cryptography—using a key distribution center (KDC). The KDC is a server that shares a unique secret symmetric key with each registered user. For Alice and Bob, denote these keys by
K_A-KDC

and
K_B-KDC
. Design a scheme that uses the KDC to distribute
K_S

to Alice and Bob. Your scheme should use three messages to distribute the session key: a message from Alice to the KDC; a message from the KDC to Alice; and finally a message from Alice to Bob. The first message is
K_A-KDC

(A, B). Using the notation,
K_A-KDC
,
K_B-KDC
,
S,
A, and
B
answer the following questions.

a. What is the second message?

b. What is the third message?