Collusion in a Multi-party Communication Protocol for Anonymous Credit Cards

We proposed in 8] a novel scheme to implement an anonymous credit card that protects privacy while providing the security, record-keeping and charging mechanism of conventional credit cards. The key idea is to use cryptographic techniques to allow two parties to communicate without knowing each other. In this paper, we present a formal method to study collusion in the multi-party communication protocol in 8]. Application of the method to our protocol leads to a simpliied implementation of anonymous credit cards that is equally secure.