A Privacy-Preserving Buyer-Seller Watermarking Protocol Based on Priced Oblivious Transfer

Buyer-seller watermarking protocols allow copyright protection of digital goods. To protect privacy, some of those protocols provide buyers with anonymity. However, anonymous e-commerce protocols pose several disadvantages, like hindering customer management or requiring anonymous payment mechanisms. Additionally, no existing buyer-seller watermarking protocol provides fair exchange. We propose a novel approach for the design of privacypreserving buyer-seller watermarking protocols. In our approach, the seller authenticates buyers but does not learn which items are purchased. Since buyers are not anonymous, customer management is eased and currently deployed methods of payment can be utilized. We define an ideal functionality for privacy-preserving copyright protection protocols. To realize our functionality, a protocol must ensure that buyers pay the right price without disclosing the purchased item, and that sellers are able to identify buyers that released pirated copies. We construct a protocol based on priced oblivious transfer and on existing techniques for asymmetric watermark embedding. Furthermore, we implement and evaluate the efficiency of our protocol, and we explain how to extend it in order to achieve optimistic fair exchange.