Towards Multiple-Payment Schemes for Digital Money

Recently, many payment schemes for digital money have been proposed. In most of these schemes money can be spent only once and must then immediately be returned to the bank. The purpose of this paper is to show the advantages of a scheme which allows the recipient of the money to use it directly for further purchases. We discuss why most existing schemes do not support such a payment scheme and make a proposal of how to overcome this drawback. Furthermore, we address the problem of achieving a fair exchange of money against service between the customer and the vendor. Few solutions to this problem have been published and all involve a trusted third party which actively supports the exchange. Using such a trustee has the disadvantage that — for high transaction rates — he easily constitutes a bottleneck. We present an alternative solution based on a `passive' trustee thereby avoiding the former disadvantage.