Research On Buyer-Seller Watermarking Protocols Based On The Assumption Of Untrusted Arbitrators

Digital watermarking technology is an effective means of digital copyright protection, however, traditional digital watermarking techniques are simply to protect the digital products sellers’legitimate interests, but they can not protect the buyers’ legitimate rights and interests. Therefore, in recent years the domestic and foreign scholars have put forward a buyer-seller watermarking protocol for buyers and sellers to trade, it plays important roles in copyright protection, piracy tracking, protecting the buyer’s and seller’s legitimate rights and interests and so on.Buyer-seller watermarking protocol has four participants in total, they are the buyer, the seller, the certification center, the arbitrator. Existing buyer-seller watermarking protocols regard the arbitrator and the certification center as trusted parties, it makes the entire protocol with multiple trusted parties, and the arbitrators are generally held by some person or some institutions in reality, so they have untrusted threat. It may occur the follow security issues when the arbitrators are not credible:First, arbitrators may collude with the buyer or the seller; Second, arbitrators may do illegal behaviors by themselves; Third, arbitrators may be attacked by malicious parties. In addition, it hasn’t designed a buyer-seller watermarking protocol which can be applied to the safe and effective multi-party transactions yet. In view of this, the research work of this thesis are as follow:Firstly, when the arbitrators are not credible, we can use a general encryption methods so that the information received by the arbitration parties is ciphertext information, thus we can address the safety issues when the arbitrators are untrusted. However, the arbitrators also need to complete the task of arbitration in the protocol, so the general encryption methods can not meet this requirement. For this reason we introduce fully homomorphic encryption, and design a safe and practical buyer-seller watermarking protocol, which implements the arbitrators extract the watermark in the ciphertext condition and complete the determination accurate.Secondly, we design a kind of buyer-seller watermarking protocol which can be applied to multi-party transactions. This protocol solves the problems of the overweight burden and long time online of the certification center, and the issues about untrusted arbitrators, making multi-party trade can be implemented safely and effectively. Thirdly, in the course of the experiment, in order to reduce the distortion rate of watermarked image, increase the correct rate of the extracted watermark, we use the watermark embedding and extraction method which combine with adding and multiplying. We also introduce fully homomorphic encryption into digital watermarking protocol, realizing that embedding and extracting watermark can be operated in the ciphertext condition. In addition, we adopt the method of mixed programming with Java and Matlab to solve low precision of the Java language in the process of image processing.Theoretical analysis and experimental results show that the two protocols which are designed in this thesis are feasible and safe, and they can be applied to the actual environment to achieve fair trade between buyers and sellers.