Direct Anonymous Attestation (DAA) is a privacy preserving authentication protocol initially designed for Trusted Platform Modules (TPMs). This cryptographic protocol, and some of its extensions such as Intel's Enhanced Privacy ID (EPID), have been widely deployed in millions of chips. Usually part of the attestation computation is delegated to the host (in most cases, either a PC or a smartphone) embedding the TPM, which is generally much more powerful. However, in Machine-to-Machine (M2M) and Internet of Things (IoT) use cases, the host may be as resource constrained as the TPM. Furthermore, any malware residing in the host may enable the tracking of the TPM owner.

Abstract 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 paper1, 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 184.25ms when the mobile is switched on, and in 266.52ms when the mobile is switched off or its battery is flat.