There was no particular notion of securing the protocol itself after the authentication phase. It's very hard to inject packets in an open TCP stream when the protocol itself is stream based. Yes, it could be done and probably more easily on WIFI than wired. Now, that said, the system was designed to address specific HEP needs with no guarantees that it would meet the needs of others. For HEP, authentication/authorization is sufficient for even drastic operations. Plus, few if any users actually use open public WiFi for xrootd connections. Plus, virtually no one would want to target physics data for destruction, if for any reasons, is that they simply don't care -- there's better data to mess with. So, there was no specific reason to complicate the protocol to address needs that just weren't there.