Suppose R is a random challenge sent in the clear from Alice to Bob and K is a symmetric key known only to Alice and Bob. Which of the following are secure session keys and which are not? Justify your...

Suppose R is a random challenge sent in the clear from Alice to Bob and K is a symmetric key known only to Alice and Bob. Which of the following are secure session keys and which are not? Justify your answers. Does this protocol provide plausible deniability? If so, why? If not, slightly modify the protocol so that it does, while still providing mutual authentication and a secure session key.

a. R®K

b. E{R,K)

c. E(K,R)

d. h(K,R)

e. h{R,K)