Key distribution is closely tied to authentication. Conference or session directory keys can be securely distributed using public-key cryptography on a one-to-one basis (by email, a directory service, or by an explicit conference setup mechanism), but this is only as good as the certification mechanism used to certify that a key given by a user is the correct public key for that user. Such certification mechanisms X.509 are not specific to conferencing, and no standard mechanisms are currently in use for conferencing purposes other than PEM[#!pem!#].
Even without privacy requirements, strong authentication of a user is required if making a network reservation results in usage based billing.