Tracing and revoking scheme for dynamic privileges against pirate rebroadcast

Abstract

Broadcast encryption provides a convenient method to distribute digital content to subscribers over an insecure broadcast channel so that only the qualified users can recover the data. Currently, there are only two broadcast encryption schemes designed for users with different privileges. In these schemes, users with higher privileges can decrypt more contents than those with low privileges, which is quite suitable for applications with different service levels. However, both schemes do not provide traitor tracing strategy. In this paper, we present a traitor tracing and revoking system for different privileges against pirate rebroadcast. We improve the tree structure and the media key block proposed by Jin and Lotspiech to suitable for applications with dynamic services, and then combine them with dynamic traitor tracing and revoking method by Kiayias and Pehlivanoglu. Dynamic services mean the users can change their privileges dynamically and the broadcast center can upgrade to hold more/less privileges when needed for marketing, while in both previous schemes the numbers of privileges are determined when the systems are setup and users’ privileges are static. Our scheme uses subset cover method to trace and revoke users so that it can trace unlimited numbers of traitors and revoke unlimited numbers of users.