= Solution
<Bilateral authentication> means that each participant obtains assurance of the other's identity and participation in the relevant run: Alice authenticates Bob and Bob authenticates Alice. An observed name in a message is not such assurance. The <protocol> must prevent an adversary from supplying the evidence while the named peer is absent.
<Session key transport> means conveying an already selected <session key> securely to its intended users. Here Tim selects $k_{AB}$ and sends it inside separate public-key-encrypted tickets for Alice and Bob. This differs from having Alice and Bob jointly derive a key to which both contribute.
$$
\boxed{\text{Both peers authenticate; Tim chooses and transports their session key.}}
$$
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