I'm preparing for an introductory information security examination in university and this is one of the tutorial question on Network Protocol attacks. I tried (a) and came to this conclusion:
Since the EPbX() is a public key encryption operation, C can decrypt any encrypted message to get back its original message, m as though it is anyone in the pair of people exchanging messages.
However, when I re-read the question, the decryption requires the use of private keys, which means it might be impossible to get the message unless C impersonates as the other to each of A and B, and is involved in the key exchange, generating 2 pairs of private keys, which seems repetitive. This confusion prevents me from doing the later part (b).
Can anyone suggest the thought process and solution to the above problem?
Here is the question description. Sorry the actual paper document is not formatted such that it allows copy over.