Under the rules of the challenge, that isn't possible since the "clients" aren't real and its just a bot they wrote. :P

All you are getting is the over-the-wire exchanges which makes it kinda a joke.

The part that is actually vulnerable to attack is the way the client functions and handles keys.

MitMing after a key exchange isn't helpful since its like getting the PGP text after its encrypted. You have to brute force the keys at that point.