A process for exchange of rights between microprocessor cards, wherein multiple keys (K1, K2, . . . ) and varied keys (Ka5, Kb3) are used. A card to be debited calculates a voucher with varied key (Ka5) that the card to be credited reconstitutes. The process has application to electronic payment....http://www.google.de/patents/US5247578?utm_source=gb-gplus-sharePatent US5247578 - Process for exchange of rights between microprocessor cards
