Untrusted
An untrusted message may be sent across either a trusted or an untrusted circuit.
Since the viewer may not establish a trusted circuit, it may only send untrusted messages. Since it is not possible for the viewer to authenticate a circuit (with the EstablishTrustedCircuit message), it cannot upgrade any circuit to trusted status, and thus must drop all trusted messages.
List of untrusted messages
[*TODO Hunting Hare 03:45, 17 January 2007 (PST)]