Abstract. NFC is a standardised technology providing short-range RFID communication channels for mobile devices. Peer-to-peer applications for mobile devices are receiving increased interest and in some cases these services are relying on NFC communication. It has been suggested that NFC systems are particularly vulnerable to relay attacks, and that the attacker's proxy devices could even be implemented using off-the-shelf NFC-enabled devices. This paper describes how a relay attack can be implemented against systems using legitimate peer-to-peer NFC communication by developing and installing suitable MIDlets on the attacker's own NFC-enabled mobile phones. The attack does not need to access secure program memory nor use any code signing, and can use publicly available APIs. We go on to discuss how relay attack countermeasures using device location could be used in the mobile environment. These countermeasures could also be applied to prevent relay attacks on contactless applications using 'passive' NFC on mobile phones.

Contactless and contact smart card systems use the physical constraints of the communication channel to implicitly prove the proximity of a token. These systems, however, are potentially vulnerable to an attack where the attacker relays communication between the reader and a token. Relay attacks are not new but are often not considered a major threat, like eavesdropping or skimming attacks, even though they arguably pose an equivalent security risk. In this paper we discuss the feasibility of implementing passive and active relay attacks against smart tokens and the possible security implications if an attacker succeeds. Finally, we evaluate the effectiveness of time-out constraints, distance bounding and the use of a additional verification techniques for making systems relay-resistant and explain the challenges still facing these mechanisms.

Contactless technology is widely used in security sensitive applications, including identification, payment and access-control systems. Near Field Communication (NFC) is a short-range contactless technology allowing mobile devices to act primarily as either a reader or a token. Relay attacks exploit the assumption that a contactless token within communication range is in close proximity, by placing a proxy-token in range of a contactless reader and relaying communication over a greater distance to a proxy-reader communicating with the authentic token. It has been theorised that NFC-enabled mobile phones could be used as a generic relay attack platform without any additional hardware, but this has not been successfully demonstrated in practice. We present a practical implementation of an NFCenabled relay attack, requiring only suitable mobile software applications. This implementation reduces the complexity of relay attacks and therefore has potential security implications for current contactless systems. We also discuss countermeasures to mitigate the attack.

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