Electronic tickets (e-tickets) are electronic versions of paper tickets, which enable users to access intended services and improve services' efficiency. However, privacy may be a concern of e-ticket users. In this paper, a privacy-preserving electronic ticket scheme with attribute-based credentials is proposed to protect users' privacy and facilitate ticketing based on a user's attributes. Our proposed scheme makes the following contributions: (1) users can buy different tickets from ticket sellers without releasing their exact attributes; (2) two tickets of the same user cannot be linked; (3) a ticket cannot be transferred to another user; (4) a ticket cannot be double spent; (5) the security of the proposed scheme is formally proven and reduced to well known (q-strong Diffie-Hellman) complexity assumption; (6) the scheme has been implemented and its performance empirically evaluated. To the best of our knowledge, our privacy-preserving attribute-based e-ticket scheme is the first one providing these five features. Application areas of our scheme include event or transport tickets where users must convince ticket sellers that their attributes (e.g. age, profession, location) satisfy the ticket price policies to buy discounted tickets. More generally, our scheme can be used in any system where access to services is only dependent on a user's attributes (or entitlements) but not their identities.
E-Ticket Schemes from Anonymous Credentials. In an anonymous credential scheme, a user can prove to a verifier that she has obtained a credential without releasing any other information. Heydt-Benjamin @cite_8 used anonymous credentials, e-cash and proxy re-encryption schemes to enhance the security and privacy of their public transport e-ticket systems. Arfaoui @cite_0 modified the signature scheme proposed Boneh al in @cite_58 to eliminate expensive pairing operations in the verification phase, and then proposed a privacy-preserving near field communication (NFC) mobile ticket (m-ticket) system by combining their modified signature with the anonymous credential scheme proposed by Camenisch al @cite_47 . In their scheme, a user can anonymously use an m-ticket at most @math times, otherwise the user is revoked by the revocation authority. These schemes can implement anonymity, ticket unlinkability as well as ticket untransferability, but, unlike our scheme, do not support privacy-preserving attribute-based ticketing. Additionally, the security of these schemes was not formally proven.
@cite_0 @cite_47 @cite_58 @cite_8
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To ensure the privacy of users in transport systems, researchers are working on new protocols providing the best security guarantees while respecting functional requirements of transport operators. In this paper, we design a secure NFC m-ticketing protocol for public transport that preserves users' anonymity and prevents transport operators from tracing their customers' trips. To this end, we introduce a new practical set-membership proof that does not require provers nor verifiers (but in a specific scenario for verifiers) to perform pairing computations. It is therefore particularly suitable for our (ticketing) setting where provers hold SIM UICC cards that do not support such costly computations. We also propose several optimizations of Boneh-Boyen type signature schemes, which are of independent interest, increasing their performance and efficiency during NFC transactions. Our m-ticketing protocol offers greater flexibility compared to previous solutions as it enables the post-payment and the off-line validation of m-tickets. By implementing a prototype using a standard NFC SIM card, we show that it fulfils the stringent functional requirement imposed by transport operators whilst using strong security parameters. In particular, a validation can be completed in 184.25 ms when the mobile is switched on, and in 266.52 ms when the mobile is switched off or its battery is flat. We propose a new and efficient signature scheme that is provably secure in the plain model. The security of our scheme is based on a discrete-logarithm-based assumption put forth by Lysyanskaya, Rivest, Sahai, and Wolf (LRSW) who also showed that it holds for generic groups and is independent of the decisional Diffie-Hellman assumption. We prove security of our scheme under the LRSW assumption for groups with bilinear maps. We then show how our scheme can be used to construct efficient anonymous credential systems as well as group signature and identity escrow schemes. To this end, we provide efficient protocols that allow one to prove in zero-knowledge the knowledge of a signature on a committed (or encrypted) message and to obtain a signature on a committed message. We describe a short signature scheme which is existentially unforgeable under a chosen message attack without using random oracles. The security of our scheme depends on a new complexity assumption we call the Strong Diffie-Hellman assumption. This assumption has similar properties to the Strong RSA assumption, hence the name. Strong RSA was previously used to construct signature schemes without random oracles. However, signatures generated by our scheme are much shorter and simpler than signatures from schemes based on Strong RSA. Furthermore, our scheme provides a limited form of message recovery. We propose an application of recent advances in e-cash, anonymous credentials, and proxy re-encryption to the problem of privacy in public transit systems with electronic ticketing. We discuss some of the interesting features of transit ticketing as a problem domain, and provide an architecture sufficient for the needs of a typical metropolitan transit system. Our system maintains the security required by the transit authority and the user while significantly increasing passenger privacy. Our hybrid approach to ticketing allows use of passive RFID transponders as well as higher powered computing devices such as smartphones or PDAs. We demonstrate security and privacy features offered by our hybrid system that are unavailable in a homogeneous passive transponder architecture, and which are advantageous for users of passive as well as active devices.