On the reliability of electronic payment systems

One of the problems facing the builders of the 'Information Superhighway' is how to charge for services. The high costs of billing systems suggest that prepayment mechanisms could play a large part in the solution. Yet how does one go about making an electronic prepayment system (or indeed any kind of payment system) robust? We describe some recent systems engineering experience which may be relevant-the successful introduction of cryptology to protect prepayment electricity meters from token fraud. These meters are used by a number of utilities from Scotland to South Africa, and they present some interesting reliability challenges.