The methods by which the necessary security requirements for messages and stored data are achieved. All three abstraction levels are tightly coupled since policy makes requirements of data flow and data flow makes requirements of mechanism. Payment Protocol Models. Cash Cash consists of a token which may be authenticated independently of the issuer. This is commonly achieved through use of self authenticating tokens or tamper proof hardware.
Cheque Cheques are payment instruments whose validity requires reference to the issuer.
Card Card payment schemes provide a payments mechanism through the existing credit card payment infrastructure. Such schemes have many structural similarities to cheque models except that solutions are constrained by that structure. A key feature of card payment systems is that every transaction carries insurance. List of Internet Payments Schemes and Proposals. See also pages by Stefan Brands Robert Hettinga and Michael Peirce .