Fault tolerant and distributed broadcast encryption

Abstract

A broadcast encryption scheme enables a server to broadcast information in a secure way over an insecure channel to an arbitrary subset of priviliged recipients. In a set-up phase, the server gives pre-defined keys to every user of the system, using secure point-to-point channels. Later on, it broadcasts an encrypted message along a broadcast channel, in such a way that only users in a priviliged subset can decrypt it, by using the pre-defined keys received in set-up phase. Usually, the broadcast message contains a fresh session key, which can subsequently be used for secure broadcast transmission to the priviliged set of recipients. In this paper we deal with two aspects of secure broadcast transmission: reliability and trust in the broadcaster. The first is a well-studied issue in communication over unreliable channels: packets can get lost and some redundancy is required to provide reliable communication. The second aspect concerns with the assumption that the broadcaster, who receives information for broadcasting from several entities, must be trusted. This issue has not previously been addressed in the broadcast transmission setting. We provide a motivating scenario in which the assumption does not hold and, for both problems, we review and extend some existing broadcast encryption schemes, in order to gain fault tolerance and to remove the need for trust in the broadcaster. © Springer-Verlag Berlin Heidelberg 2003.