MOTET: Mobile Transactions using Electronic Tickets

There has been considerable work within the field of digital cash protocols that aims to provide security guarantees - non-repudiation, authentication, overspending checking and off-line checking - whilst protecting anonymity. However, considerably less attention has been given to the question of electronic ticketing, and what exists has been rather abstract or limited. Although eTickets aim at providing the same security guarantees and privacy preservation properties as digital cash, they are significantly different. Digital cash derives much of its anonymity from the fact that the denominations of electronic coins and notes are sufficiently universal that it is not possible for the bank to know in advance how they might be spent. In an eTicketing system, however, this is not the case: at the point the ticket is purchased, the ticket vendor knows for what it will be used and, if a non-anonymous payment system is used, can associate this with the customer. We present a novel protocol that enables users to purchase and spend electronic tickets (eTickets) of a range of two different types: those that can only be used a certain number of times, and those that expire after a certain date.