ABSTRACT
Physical distance serves as a measure of trust and in some systems users are granted privileges based on their perceived location. Radio-frequency identification (RFID) tokens are often used for proximity identification due to their limited range of communication. RFID systems are, however, particularly vulnerable to relay attacks, which allow an attacker to pretend that a valid token is present by relaying the communication between a reader and a remote token. The increasing availability of RFID equipment for development makes relay attacks relatively easy to implement. Distancebounding protocols allow a device to cryptographically determine an upper bound on the distance to another device and are an effective countermeasure against relay attacks. RFID systems would therefore benefit from distance-boundingprotocols even though the practical implementation of suitable cryptographic mechanisms and communication channel requires careful consideration because of resource constraints. This chapter describes the implementation of relay attacks against RFID
tokens and discusses several protocols and communication channels, which have been proposed for cryptographically bounding the distance to low-resource tokens.
