Over the past decade, smartphones have become the point of convergence for many applications and services. There is a growing trend in which traditional smart-card based services like banking, transport and access control are being provisioned through smartphones. Smartphones with Near Field Communication (NFC) capability can emulate a contactless smart card; popular examples of such services include Google Pay and Apple Pay. Similar to contactless smart cards, NFC-based smartphone transactions are susceptible to relay attacks. For contactless smart cards, distance-bounding protocols are proposed to counter such attacks; for NFC-based smartphone transactions, ambient sensors have been proposed as potential countermeasures. In this study, we have empirically evaluated the suitability of ambient sensors as a proximity detection mechanism for contactless transactions. To provide a comprehensive analysis, we also collected relay attack data to ascertain whether ambient sensors are able to thwart such attacks effectively. We initially evaluated 17 sensors before selecting 7 sensors for in-depth analysis based on their effectiveness as potential proximity detection mechanisms within the constraints of a contactless transaction scenario. Each sensor was used to record 1000 legitimate and relay (illegitimate) contactless transactions at four different physical locations. The analysis of these transactions provides an empirical foundation on which to determine whether ambient sensors provide a strong proximity detection mechanism for security-sensitive applications like banking, transport and high-security access control.
@cite_7: • Using ambient sensors: to measure the characteristics of the surrounding environment, such as light, sound, temperature and GPS. The underlying assumption is that the malicious and honest readers should be in two different locations with different environments. • Problem: All these solutions will not work if the two readers are located in the same environment (e.g., in two nearby stalls in the same mall). In this work, we present TTP as a countermeasure that defends against the reader-and-ghost attack even when the malicious and honest readers are in the same environment. Our solution is based on the following observation: As the result of physical tapping between a pair of sensor-rich devices (say two NFC-enabled phones acting as a card and a reader), the tapping event causes unpredictable but strongly correlated vibrations at both sides, which are hard to reproduce and can be reliably measured by accelerometer sensors.
@cite_7 proposed the use of an accelerometer to provide assurance that the mobile phone is within the vicinity of the payment terminal. Their proposal requires the user to tap the payment terminal twice in succession, after which the sensor streams of the device and the payment terminal are compared for similarity. It is difficult to deduce the total time it took to complete one transaction in its entirety, but the authors have provided a sensor recording time range of 0.6--1.5 seconds.