Metering Schemes for General Access Structures

A metering scheme is a method by which an audit agency is able to measure the interaction between servers and clients during a certain number of time frames. Naor and Pinkas 7] considered schemes in which any server is able to construct a cryptographically secure proof if and only if it has been visited by at least a number, say h, of clients in a given time frame. In this paper we construct metering schemes for more general access structures, which include multilevel and compartmented access structures. Metering schemes realizing these access structures have useful practical applications: for example, they can be used to measure the interaction of a web site with a speciic audience which is of special interest. We also prove lower bounds on the communication complexity of metering schemes realizing general access structures.