Diffie-hellman key exchange. (4 marks) holmes and watson generate a key for use in secure communication using the dhke. they use the prime p= 13 and the generator a = 7 of the group z12. holmes' private key is a = 3 and watson's private key is b=5. (a) calculate holmes and watson's public keys i. e. the numbers they send each other. (b) calculate the shared private key they will use to communicate. (c) state which numbers are available in the public domain? which numbers are private?