a) Describe how the Diffie Hellman Key Exchange protocol allows for the generation of a shared key. What are the possible attacks on such a protocol? Assume that Alice and Bob have a common primitive q=23 and a primitive root a=5. i) If Alice has public key Ya=10, show the process and derive the value of Alice's private key XA. ii) If Bob has the public key YB = 8, what is the value of the shared secret key K? [30 marks] b) Alice wants to use AES to send emails to Bob. Which AES encryption mode would be appropriate and how will this ensure confidentiality and integrity of the emails? [20 marks]