Definition of Protocols for Secure Anonymous Purchase Borja Richart 1 , Ramon Martí 1 , Jaime Delgado 1 , Abdul H. Sadka 2 , Peter Sweeney 2 1 Universitat Pompeu Fabra (UPF) borja.richart01@campus.upf.es, ramon.marti@upf.edu, jaime.delgado@upf.edu 2 CCSR, University of Surrey (UniS) a.sadka@surrey.ac.uk, p.sweeney@surrey.ac.uk Abstract Digital watermarking is the art of hiding information in digital contents such as images, audio clips, and videos. We can take advantage of this technique by adding author information as well as buying information for a digital purchase. In this paper we propose a protocol for secure anonymous digital purchase to deter buyers from executing illegal redistribution of digital contents. We propose a protocol to allow merchants to obtain a proof of treachery from dishonest buyers. 1. Introduction This paper describes the idea of asymmetric schemes applied to secure anonymous digital purchases. This work has been divided in research of three parts: - Buyer's registration: Design of a protocol that guarantees the anonymity of buyers in any digital purchase. Moreover, it will help to unmask the fraudulent buyers (they will loose their anonymity). - Digital purchase: Proposal of an architecture between buyers, merchants and a trusted third party (also known as asymmetric server) who will carry out the watermark process. - Unmask the dishonest buyers: If merchants find out an illicit copy of the content they have sold, they will have a proof of treachery to denounce buyers. This is the aim of that protocol. Inverse watermarking techniques will be useful to recover the buyer identity. 2. Motivation Nowadays we live with a great variety of audiovisual content in digital format. The digital format has a lot of advantages over the analogical format, such as the easiness producing perfect digital copies. That is the reason why part of providers are reticent to offer their services on-line, since they want to avoid illegal copies and free distribution of copyrighted data. Different methods have been used through history, to guarantee intellectual property and privacy. For example: the signature of the artist on a painting; the mark of a ring on sealing wax; ISBN number in a book, etc. However, the digital world introduces a different kind of problems. One can very easily modify and copy any kind of file. The drawback of this technological improvement is the illicit distribution of copies, at very low cost and without any deterioration of the quality. This is why we need more sophisticated methods to ensure their protection. A great deal of attention is currently paid to approaches aiming at protecting authors'/creators' rights. A lot of research work has been invested into the design of methods that technically support the copyright protection of digital data. One class of such methods consists of techniques called fingerprinting schemes. The other class of such methods is called watermarking schemes. Watermarking is clearly one of the reasonable alternatives to solve several problems such as violation of ownership and illegal distribution of copies. It enables the owner of a digital asset to embed some information in the digital content and to extract it. Moreover, it enables a merchant to trace the buyer from the illegally redistributed copy. It is in that point where we are focusing our research. 3. Background & State of the Art 3.1. Digital Purchase (e-commerce) E-commerce provides an additional method for buying or selling. In traditional sales, the buyer and/or the salesman are the active parties. In one case, the buyer initiates the purchase by either going to the store