Returning of change in an electronic payment system

摘要

The invention relates to a method of returning change to a payer in an electronic payment system. A payer determines a change return value, generates and blinds a change return certificate, generates a first signature by signing the blinded change return certificate, and sends a message comprising the first signature to a payee. The payee forwards the message to a payment provider. The payment provider verifies the first signature and the change return value indicated by the message, generates a blinded second signature by signing the blinded change return certificate, and forwards the blinded second signature to the payer. The payer unblinds and verifies the blinded second signature, and forms a second payment certificate. The invention furthermore relates to a method of performing tasks of a payer and to a method of performing tasks of a payment provider in a change return transaction, to computer programs and devices therefore.