Secure closed-door video conferencing will be an important application to conduct business meetings over the Internet. The ``close-door'' policy implies a strong confidentiality requirement. No one other than the group members may send messages to and receive messages from the group. We therefore get a weak authorization since only group members can send valid messages to the group. The authorization is weak because we don't have a fine granularity for sender access control.
By encrypting all group communications we get anonymity and privacy to eavesdropper. Only if any eavesdropper has the possibility to join the group we loose anonymity. The anonymity is therefore dependent on the group join policy.