Untraceable Fair Network Payment Protocols with Off-Line TTP

A fair network payment protocol plays an important role in electronic commerce. The fairness concept in payments can be illustrated as that two parties (e.g. customers and merchants) exchange the electronic items (e.g. electronic money and goods) with each other in a fair manner that no one can gain advantage over the other even if there are malicious actions during exchanging process. In the previous works of fair payments, the buyer is usually required to sign a purchase message which can be traced by everyone. The information about where the buyer spent the money and what he purchased would easily be revealed by this way. This paper employs two techniques of off-line untraceable cash and designated confirmer signatures to construct a new fair payment protocol, in which the untraceability (or privacy) property can be achieved. A Restrictive Confirmation Signature Scheme (RCSS) will be introduced and used in our protocol to prevent the interested persons except the off-line TTP (Trusted Third Party) from tracing the buyer’s spending behavior.