Attacks On Two Buyer-Seller Watermarking Protocols And An Improvement For Revocable Anonymity

Buyer-seller watermarking protocols incorporate digital watermarking with cryptography, in order to protect digital copyrights and privacy rights for the seller and the buyer before, during, and after trading activities in e-commerce. In this paper, we present attacks on two recently proposed buyer-seller watermarking protocols, and prove that these protocols are not able to provide security for both the buyer and the seller simultaneously. Further, we point out that both protocols don't function properly when employing homomorphic probabilistic cryptosystems. We also show that the buyer's anonymity and/or the transaction unlinkability is not achieved in these protocols. We propose an improved secure and anonymous buyer-seller protocol, which is secure and fair for both the seller and the buyer In contrast to early work, our scheme is able to provide all the security properties that a secure buyer-seller watermarking protocol is expected to hold.