A reusable public transport electronic ticket system with fast validation

This paper presents an electronic ticket system for public transport which provides reusability in the sense that, after the validation of a ticket, a traveler is enabled to perform a journey which can include a limited number of transfers before an expiration time. The proposal has been designed following a privacy-by-design approach. Travelers are only required to identify themselves if requested to prove possession of a valid ticket by an officer. Otherwise, they can travel without being required to disclose their identity (anonymity). Also, the diverse interactions of a traveler with the system cannot be related to them (unlinkability). The security and privacy requirements are achieved by making use of advanced cryptographic techniques. The system has been simulated and proven to provide running times which make it appropriate for a real deployment. When compared to an existing proposal designed for an equivalent scenario, the reduction in the time required for ticket validation is especially remarkable. In effect, all the use cases with real-time constraints (“Ticket validation”, “Get-in”, and “Get-out”) can be run in less than one second.