An electronic payment system ideally should provide security, anonymity, fairness, transferability and scalability. Existing payment schemes often lack either anonymity or scalability. In this paper we propose WhoPay, a peer-to-peer payment system that provides all the above properties. For anonymity, we represent coins with public keys; for scalability, we distribute coin transfer load across all peers, rather than rely on a central entity such as the broker. This basic version of WhoPay is as secure and scalable as existing peer-to-peer payment schemes such as PPay, while providing a much higher level of user anonymity. We also introduce the idea of real-time double spending detection by making use of distributed hash tables (DHT), which further improves the security level of WhoPay.
To evaluate how well WhoPay distributes load among peers, we have run simulations with several different configurations. The simulation results show that the majority of the system load is handled by the peers under typical peer availability, indicating that WhoPay should scale well.