An Asymmetric Traceability Scheme for Copyright Protection without Trust Assumptions

Abstract.

Traceability schemes have been proposed as a method to establish copyright protection of broadcast information. With asymmetric traceability, the content provider cannot frame an innocent user, while no user can abuse the system (construct or help constructing a "pirate" decoder) without being detected. We propose an asymmetric solution for traceability, based on the very efficient symmetric scheme of Kurosawa-Desmedt. We do not make any trust assumptions about the broadcasting center or other authorities. Furthermore, we establish anonymity protection for all honest users: the identity of a user is protected, until a "fingerprint" of that user is found on a pirate decoder. For asymmetric construction of the fingerprints we make use of Oblivious Transfer techniques. We also propose a Cut-and-Choose technique to assure the correctness of the decryption keys.

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