Anonymity is one of important requirements for electronic marketplaces to offer similar privacy as current marketplace. Unfortunately, most watermarking protocols in the literature have been developed without considering a buyer's anonymity. It would be unsatisfactory for the buyer to reveal his/her identity to purchase multimedia contents. In this paper we propose an anonymous buyer-seller watermarking protocol, where a buyer can purchase contents anonymously, but anonymity control is provided, i.e., a seller can trace the identity of a copyright violator. The proposed scheme also provides unlinkability of contents purchased by a buyer. Another distinct feature of our scheme is that the identification of an illegal buyer is accomplished in a way such that the seller can directly convince a judge that the buyer has redistributed contents. This feature removes any possibility of dispute. Furthermore, when the innocent buyer is falsely accused by a malicious seller, it is possible to prove his/her innocence without attending a court and revealing any privacy.
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