During the last 20 years, electronic commerce has become a vast growing area in computer science. The most commonly used forms are business-to-business (B2B) electronic commerce, which normally involves a long-term relationship between enterprises, and business-to-consumer (B2C) electronic commerce, which is for instance online trading between a single person and a merchant. One of the problems of existing electronic payment systems like SET are, that they put the merchant in control of the trading process and information flow. In addition to that, existing protocols don't combine the payment and fulfillment. Therefore if a merchant doesn't deliver the goods or the goods were delivered but don't meet the buyer's expectations, payment has occurred already in most cases. The buyer then has to dispute this transaction which might or might not be successful. The protocol that is described here instead switches the control over from the merchant to the purchaser. This is achieved by introducing the concept of a payment token that is only valid if it is presented together with a key that unlocks the payment. The payment token is - like a check - a promise to pay the specified amount. However, the merchant has to trust this payment token and after successful delivery of the goods or performance of the ordered services, the buyer provides if the goods meet his expectations the key to the merchant, who then collects payment from his bank. In addition to the specification, informal validation and evaluation of the designed protocol RCCP, the underlying security techniques will be presented to the reader and in order to be able to compare RCCP to already existing techniques, several payment systems that are in use today are introduced. lt should be mentioned here however, that the name RCCP - reverse credit card payment - has become rather outdated during the course of the project and thus is not used in this thesis, since the protocol that has been designed is no longer just a payment protocol. As RCCP includes fulfillment issues, the category trading protocol seems more appropriate.