Scalable public-key tracing and revoking

Abstract. Traitor Tracing Schemes constitute a very useful tool against piracy in the context of digital content broadcast. In such multi-recipient encryption schemes, each decryption key is fingerprinted and when a pirate decoder is discovered, the authorities can trace the identities of the users that contributed in its construction (called traitors). Public-key traitor tracing schemes allow for a multitude of nontrusted content providers using the same set of keys, which makes the scheme “server-side scalable.” To make such schemes also “client-side scalable, ” i.e. long lived and usable for a large population of subscribers that changes dynamically over time, it is crucial to implement efficient Add-user and Remove-user operations. Previous work on public-key traitor tracing did not address this dynamic scenario thoroughly, and there is no efficient scalable public key traitor tracing scheme that allows an increasing number of Add-user and Remove-user operations. To address these issues, we introduce the model of Scalable Public-Key Traitor Tracing, and present the first construction of such a scheme. Our model mandates for deterministic traitor tracing and an unlimited number of efficient Add-user operations and Remove-user operations. A scalable system achieves an unlimited number of revocations while retaining high level of efficiency by dividing the run-time of the system into periods. Each period has a saturation level for the number of revocations. When a period becomes saturated, an efficien