Off-Line Electronic Cash Based on Secret-Key Certificates

An oo-line electronic coin system is presented that ooers multi-party security and unconditional privacy of payments. The system improves signiicantly on the eeciency of the previously most eecient such system known in the literature, due to application of a recently proposed technique called secret-key certiicates. By deenition of secret-key certiicates, pairs consisting of a public key and a matching certiicate can be simulated with indistinguishable probability distribution. This allows a variety of polynomial-time reductions from a well-known signature scheme to the cash system. In particular, the withdrawal protocol can be proved to be restrictive blind with respect to one account holder, relying only on a standard intractability assumption; no such result has been proved before in the literature. Another consequence of the application of the secret-key certiicate technique is that the withdrawal protocol is not a blind signature issuing protocol. This falsiies the popular belief that eecient privacy-protecting oo-line electronic cash systems must be based on withdrawal protocols that are blind signature issuing protocols.