Towards transferable watermarks in buyer-seller watermarking protocols

Buyer-seller watermarking protocols are protocols that let a seller embed a watermark which uniquely identifies the buyer of each sold copy of some work without allowing the seller to learn the watermark. The purpose of such protocols is to deter buyers from illegally redistributing the work while protecting the buyer from being framed by dishonest sellers. Existing buyer-seller watermarking schemes require that every buyer receives his or her copy directly from the seller. We consider the problem of extending buyer-seller watermarking to allow (controlled) redistribution between buyers while maintaining a watermark that uniquely identifies each recipient. An efficient and secure protocol of this type could allow distribution of digital content in peer-to-peer networks while protecting the owner´s copyright. We give a proof-of-concept protocol which only requires limited interaction with the original seller to change the watermark.