P4R: Privacy-Preserving Pre-Payments with Refunds for Transportation Systems

Andy Rupp, Gesine Hinterwälder, Foteini Baldimtsi, Chris­tof Paar

A.-R. Sadeghi (Eds.): Financial Cryptography and Data Security 2013, Volume 7859, pp 205-212, 2013. © Springer-Verlag Berlin Heidelberg 2013


We propose a new lightweight payment scheme for transit systems called P4R: Privacy-Preserving Pre-Payments with Refunds. In P4R a user deposits money to obtain a bundle of credentials, where each credential allows to make an arbitrary ride. The actual fare of a trip is determined on-the- y when exiting. Overpayments are refunded where all trip refunds of a user are aggregated in a single token thereby saving memory and increasing privacy. We build on Brands' e-cash scheme to realize the pre-payment system and a new variant of blind Boneh-Lynn- Shacham signatures to implement the refund capabilities. Our construc- tion is secure against malicious users and guarantees user privacy. We also provide an ecient implementation that shows the suitability of our scheme as future transit payment system.