(a) How do Alice and Bob set up a way to communicate such that Eve cant intercept and under- stand their messages?

(b) Is it guaranteed that Eve wont be able to decrypt Alice and Bobs messages?

c) Suppose that you had both a secure and an insecure channel (Eve can only intercept messages sent through the insecure channel), but that the secure channel was much more expensive to use than the insecure channel. Would Diffie-Hellman exchange still be necessary in this case? Explain your answer.