Flow Control: A New Approach for Anonymity Control in Electronic Cash Systems

Anonymity features of electronic payment systems are im- portant for protecting privacy in an electronic world. However, complete anonymity prevents monitoring financial transactions and following the money trail, which are important tools for fighting serious crimes. To solve these type of problems several “escrowed cash” systems, that allow a “Trustee” to trace electronic money, were suggested. In this paper we suggest a completely different approach to anonymity control based on the fact that law enforcement is mainly concerned with large anonymous electronic payments. We describe a payment system that effectively lim- its the amount of money a user can spend anonymously in a given time frame. To achieve this we describe a technique to make electronic money strongly non-transferable. Our payment system protects the privacy of the honest user who plays by the rules, while introducing significant hurdles for several criminal abuses of the system.