An Asymptotically Optimal RFID Authentication Protocol Against Relay   Attacks
  Relay attacks are a major concern for RFID systems: during an authentication process an adversary transparently relays messages between a verifier and a remote legitimate prover.   We present an authentication protocol suited for RFID systems. Our solution is the first that prevents relay attacks without degrading the authentication security level: it minimizes the probability that the verifier accepts a fake proof of identity, whether or not a relay attack occurs. 
Gildas Avoine and Aslan Tchamkerten