A buyer-seller watermarking protocol

Digital watermarks have previously been proposed for the purposes of copy protection and copy deterrence for multimedia content. In copy deterrence, a content owner (seller) inserts a unique watermark into a copy of the content before it is sold to a buyer. If the buyer sells unauthorized copies of the watermarked content, then these copies can be traced to the unlawful reseller (original buyer) using a watermark detection algorithm. One problem with such an approach is that the original buyer whose watermark has been found on unauthorized copies can claim that the unauthorized copy was created or caused (for example, by a security breach) by the original seller. In this paper, we propose an interactive buyer-seller protocol for invisible watermarking in which the seller does not get to know the exact watermarked copy that the buyer receives. Hence the seller cannot create copies of the original content containing the buyer´s watermark. In cases where the seller finds an unauthorized copy, the seller can identify the buyer from a watermark in the unauthorized copy and furthermore the seller can prove this fact to a third party using a dispute resolution protocol. This prevents the buyer from claiming that an unauthorized copy may have originated from the seller