A Generalization of an Anonymous Buyer-Seller Watermarking Protocol and Its Application to Mobile Communications

Buyer-seller watermarking schemes enable sellers to identify the buyer of illegally distributed contents by providing each buyer with a slightly different version. To protect the privacy of buyers, buyers' purchase should be done anonymously, and unlinkability of contents purchased should be satisfied. In this paper, our concern is to generalize a buyer-seller watermarking protocol to multi-purchase environments. The problem of most schemes in the literature is that the number of keys held by buyer's devices increases in proportion to that of contents purchased, if we apply it to multi-purchase case. Otherwise, they cannot provide unlinkability. We propose an efficient multi-purchase buyer-seller watermarking protocol satisfying anonymity and unlinkability, where a buyer executes registration step one time and the number of buyer's necessary key is also one regardless of that of contents. Our second concern is to extend this scheme to the mobile communications. Our scheme reduces amount of buyers' computations to the minimum by introducing a concept of mobile agents.