Buyer-seller watermarking protocols integrate multimedia watermarking and fingerprinting with cryptography, for copyright protection, piracy tracing, and privacy protection. We propose an efficient buyer-seller watermarking protocol based on dynamic group signatures and additive homomorphism, to provide all the required security properties, namely traceability, anonymity, unlinkability, dispute resolution, non-framing, and non-repudiation. Another distinct feature is the improvement of the protocol’s utility, such that the double watermark insertion mechanism is avoided; the final quality of the distributed content is improved; the communication expansion ratio and computation complexity are reduced, comparing with conventional schemes.