Proxy signatures and buyer–seller watermarking protocols for the protection of multimedia content

Abstract

Watermarking techniques are developed to deal with multimedia distribution, authentication and copyright protection. It is usually the seller who embeds a watermark in multimedia content to identify the buyer. The embedded watermark can then be used to trace the traitors identity if unauthorized copies are found. However, repudiation and framing issues might arise in this approach. To solve these problems, buyer---seller watermarking protocols have been proposed based on watermarking in the encrypted domain. Such watermarks combine encryption, digital watermarking, and fingerprinting to preserve digital rights of both the buyer and the seller. Unfortunately, most existing watermarking techniques do not provide convincing proofs to ensure that they achieve the claimed level of security and informal proofs abound in the literature. In this paper, we propose a buyer---seller watermarking protocol based on proxy signatures and homomorphic encryption. Formal proofs are provided to show that in the proposed protocol, watermarks are generated such that the seller is unable to fabricate piracy, but he can trace copyright violators. The protocol further protects anonymity of the buyer until he is adjudicated to be guilty. Moreover, we solve the conspiracy problem without imposing any unrealistic assumptions about thrust-worthiness of the parties involved.