Electronic Cash with Anonymous User Suspension

Electronic cash (E-cash) is the digital counterpart of cash payment. They allow users to spend anonymously unless they “double spend” their electronic coins. However, it is not possible to prevent users from misbehaving under some other subjective definitions of misbehavior, such as money laundering. One solution is to incorporate a trusted third party (TTP), which, upon complaint, uses its power to deanonymize the suspected user. This solution, known as fair e-cash, is not fully satisfactory since additional measure has to be taken to stop misbehaving users from further abusing the system after they have been identified. We present a e-cash system with anonymous user suspension, EC-AUS, which features an suspension manager (SM) that is capable of suspending the underlying user that participates in any suspicious transaction. Suspended users cannot participate in any transaction. The suspension is anonymous in the sense that no party, not even SM, can tell the identities of the suspended users nor link their past transactions. If they are found innocent later, their suspension can be revoked easily.