Near Field Communication (NFC) has enabled mobile phones to emulate contactless smart cards. Similar to contactless smart cards, they are also susceptible to relay attacks. To counter these, a number of methods have been proposed that rely primarily on ambient sensors as a proximity detection mechanism (also known as an anti-relay mechanism). In this paper, we, for the first time in academic literature, empirically evaluate a comprehensive set of ambient sensors for their effectiveness as a proximity detection mechanism. We selected 15 out of a total of 17 sensors available via the Google Android platform for evaluation, with the other two sensors unavailable on widely-used handsets. In existing academic literature, only 5 sensors have been proposed with positive results as a potential proximity detection mechanism. Each sensor, where feasible, was used to record the measurements of 1000 contactless transactions at four different physical locations. A total of 252 random users, random sample of the university student population, were involved during the field trails. The analysis of these transactions provides an empirical foundation to categorically answer whether ambient sensors provide a strong proximity detection mechanism for security sensitive applications like banking, transport and high-security access control. After careful analysis, we conclude that no single evaluated mobile ambient sensor is suitable for such critical applications in realistic deployment scenarios. Lastly, we identify a number of potential avenues that may improve their effectiveness.
@cite_13: Unless specifically designed for its prevention, none of the existing RFID authentication protocols are immune to relay attacks. Relay attacks generally involve the presence of one or more adversaries who transfer unmodified messages between a prover and a verifier. Given that the message content is not modified, it is rather difficult to address relay attacks through cryptographic means. Extant attempts to prevent relay attacks involve measuring signal strength, round-trip distance, and ambient conditions in the vicinity of prover and verifier. While a majority of related authentication protocols are based on measuring the round-trip distance between prover and verifier using several single-bit challenge-response pairs, recent discussions include physical proximity verification using ambient conditions to address relay attacks. We provide an overview of existing literature on addressing relay attacks through ambient condition measurements. We then propose an elliptic curve-based mutual authentication protocol that addresses relay attacks based on (a) the surface temperature of the prover as measured by prover and verifier and (b) measured single-bit round-trip times between prover and verifier. We also evaluate the security properties of the proposed authentication protocol.
@cite_13 use ambient temperature with an elliptic curve-based RFID NFC authentication protocol to determine whether two devices are co-located. Using this method, they were successful in establishing a secure channel; the proposal combines the timing channels in RFID, traditionally used in distance bounding protocols, in conjunction with ambient temperature. Their proposal, however, was not implemented and so there is no experimental data provided to evaluate its efficacy.