Security Analysis and Implementation of Relay-Resistant Contactless Payments

Abstract

Contactless systems, such as the EMV (Europay, Mastercard and Visa) payment protocol, are vulnerable to relay attacks. The typical countermeasure to this relies on distance bounding protocols, in which a reader estimates an upper bound on its physical distance from a card by doing round-trip time (RTT) measurements. However, these protocols are trivially broken in the presence of rogue readers. At Financial Crypto 2019, we proposed two novel EMV-based relay-resistant protocols: they integrate distance-bounding with the use of hardware roots of trust (HWRoT) in such a way that correct RTT-measurements can no longer be bypassed. Our contributions are threefold: first, we design a calculus to model this advanced type of distance-bounding protocols integrated with HWRoT; as an additional novelty, our calculus is also the first to allow for mobility of cards and readers during a proximity-checking phase. Second, to make it possible to analyse these protocols via more standard mechanisms and tools, we consider a 2018 characterisation of distance-bounding security that does away with physical aspects and relies only on the causality of events; we cast it in our richer calculus and extend its theoretical guarantees to our more expressive models (with mobility, potentially rogue readers, and HWRoT). Due to this extension, we can carry out the security analysis in the standard protocol verification tool ProVerif. Third, we provide the first implementation of Mastercard's relay-resistant EMV protocol PayPass-RRP as well as one of its 2019 extension with HWRoT called PayBCR. We evaluate their efficiency and their robustness to relay attacks, in presence of both honest and rogue readers. Our experiments are the first to show that Mastercard's PayPass-RRP and its HWRoT-based extension PayBCR are both practical in preventing relay attacks of the magnitude shown thus-far in EMV.