a. For Diffie-Hellman key exchange algorithm, explain the assumptions under which it is secure. (5 points) b. Without the assumptions mentioned in question (a), will it be vulnerable to a certain kind of attack? What is this attack? Describe it in detail. (10 points) c. During the key exchange, sender and receiver can calculate the final shared key. Please prove the calculated shared keys K of the sender and receiver are the same. (10 points)