Consider the following authentication protocol SKID2/SKID3 that uses symmetric cryptography. It assumes that Alice and Bob share a secret key K. SKID2 allows Bob to authenticate to Alice and proceeds as follows:

Alice chooses a random number RA and sends it to Bob.

Bob chooses a random number RB and sends to Alice RB , MACK (RA, RB , B).

Alice computes MACK (RA, RB , B) and compares it with what the received from Bob. If the results are identical, then Alice knows that she is communicating with Bob.

SKID3 provides mutual authentication between Alice and Bob. Steps (a)(c) are the same as in SKID, and then the protocol proceeds with:

Alice sends Bob MACK (RB , A).

Bob computes MACK (RB , A) and compares it with what he received from Alice. If the results are identical, then Bob knows that he is communicating with Alice.

Answer the following questions about the protocol:

If Mallory was to mount a man-in-the-middle attack, describe how she is to proceed. What would happen in the protocol as a result of her attack? Can Mallory succeed?

Repeat part (a) for a parallel session attack.