Confidence in smart token proximity: Relay attacks revisited

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.