(a) The ephemeral Diffie-Hellman Key Exchange (DHKE) protocol allows two parties to agree on keying material in the presence of an adversary. The protocol assumes the two parties already agreed on two primes p, q such that q divides p - 1 and a value> 1 such that of 1 mod n From this starting point, describe the remainder of the protocol, recalling that the ephemeral version of the protocol involves the exchange of fresh Diffie-Hellman values.[6 marks] (b) Assuming that the adversary is passive (i.e. acts only as an eavesdropper), identify the computational problem underlying the security of this protocol. How does it relate to the Discrete Logarithm Problem (DLP) in the given setting? [4 marks] (c) How large should p and q be so that the ephemeral DHKE protocol in your answer to Question 4(a) is secure against an adversary willing to expend an effort of 280 basic operations? What if the adversary is willing to expend an effort of 2128 basic operations? Justify your answers with reference to algorithms for solving the DLPin the given setting.[6 marks] (d) Discuss the security weaknesses of ephemeral DHKE in the situation where the adversary is an active party. (e) Explain how you might modify the ephemeral DHKE protocol to avoid the weak-nesses identified in your answer to Question 4(d).[4 marks] (f) The ElGamal Public key encryption (PKE) scheme is derived from the Diffie-Hellman key exchange algorithm. Describe the El Gamal algorithm, and the relationship be-tween DHKE and the EI Gamal PKE.[4 marks] (g) Public key encryption can also be used to establish keying material in the presence of an adversary. (i) Describe a simple protocol for achieving this. (ii) Compare and contrast the approaches based on PKE and ephemeral DHKE[4 marks]in terms of security and efficiency.