Performance Evaluation of Brands’ Digital Cash System in TCP/IP Environment zyx Pock-Chueng Teo Ahmad Zuri Sha’aineri Mohsen Ashourian Revol Technologies; Universiti Teknologi Islamic Azad University of Singapore Malaysia Iran-Majlesi Branch lawrencetco@yahoo.com Abstract zyxwvutsrqpo - Brands’ digital cash system is a single term system that builds on two concepts, Schnorr digital signature and the representation problem in group of prime order. The Brands’ scheme is almost as efficient as fully traceablc offline systems. In this paper, we evaluate the perfomiance of Brands’ system in TCP/IP Environment and report the results in various conditions. 1. INTRODUCTION The advent of electronics changes the face of the world. The advantage of electronics can be defined in three categories - compcitation, communication and storage, with the features of fast, accurate and persistent. Consequently, electronics found its applications in a wide variety of domains. zyxwvutsr In the endless list of application domains, commerce is not an exception. Electronic commerce is a contemporary term denoting the commerce activities conducted using electronic mechanism, either directly or indircctly, in front of or behind the scene. Computation, communication and storage are the three elementary components in electronic commerce that work in a highly interactive manner to fully exploit the advantage that could not be obtained in the traditional commerce. Electronic payment as the final stage in electronic commerce plays an important role. Without proper and efficient electronic payment mcclianism, electronic commerce cannot fully demonstrate its real potential. Digital cash is a class of electronic payment that emphasizes security, convenience, and anonymity. 2. BRANDS’ DIGITAL CASH SCHEME The Brands’ digital cash scheme is an offline anonymous digital cash scheme developed based on an underlying number theory hard problem known as the ‘representation problem’ [I]. The representation problem is believed to be equivalent in coinpiitational difficulty to computing discrete logarithms, rather than RSA root. Hence, the mathematical breakthrough in factoring method does not reduce the security of Brands’ digital cash system. Brands’ digital cash schemc involves three entities and consists of four protocols. A bank plays the role of an authorized digital cash issuer. zyxwvutsrq A user withdraws digital cash from thc bank and pays the digital cash to a merchant in exchange for goods and services. The merchant finally deposits the digital cash back to the bank. The Brands’ digital cash transaction is therefore the circulation of the Brands’ digital cash token bctwccn thc three entities. This paper uses the terms merchant and shop intcrchangcably to denote thc party who sclls goods or services to the user. The Brands’ scheme is an untraceable offline digital cash scheme. Due to the nature of the two features - untraceable and offline, the integration into a single scheme is not trivial. The Brands’ scheme applies subtle techniques to simultaneously achicvc the two primary aspects of security and anonymity. The bank digitally signs on digital cash token in order to make the token, valid for transaction. The digital signatiire scheme used by the bank is sufficiently strong to resist the possibility of signature forgery by attackers. To protect the anonymity of the user, Brands’ schemc allows thc uscr to execute restrictive blinding on the digital cash tokcn to be signed. The restrictive blinding ensures that the user can only change the external appearance of the token while the internal token structure embedded with the user’s identity information shall remain intact. This implies that the user is not able to destroy the internal token structure, which aids owner tracing in thc case of double spending. through the blinding process. The restrictive blinding withdrawn and deposited digital cash tokens and thus protecting the user anonymity. To use the digital cash token in the payment protocol, the user needs to prove his ownership over thc tokcn. The ownership is proven through the knowlcdge of representation on the token. Uiidcr the assumptions of Discrete Logarithm and Diffie-Hellinan, no one except the legal tokcn owner could provide such a proof of ownership. Additionally, the user would release partial information during the proof of ownership. A single piecc of such partial ,information does not lead to the revelation of the user identity; howevcr two pieces do. The bank is able to trace to the double spender tliroiigh this mechanism. In other words, the Brands’ schcmc provides a means to expose the double spender’s identity after the fact. 3. IMPLEMENTATION OF BRANDS’ SYSTEM Thc Brands’ scheme consists of 4 different protocols - namely Setup, Withdrawal. Payment and Deposit. Account Setup needs to be done only once when thc user creates an account at the particular bank. Thercaftcr, the uscr needs to carry out the reinaining three protocols for future digital cash transaction. A completc digital cash . prevents the bank froin bcing able to match the Authorized licensed use limited to: UNIVERSITY TEKNOLOGI MALAYSIA. Downloaded on January 5, 2009 at 03:30 from IEEE Xplore. Restrictions apply.