Date Added: Jul 2012
Privacy of RFID systems is receiving increasing attentions in the RFID community and an important issue required as to the security of RFID system. Backward privacy means the adversary cannot trace the tag later even if he reveals the internal states of the tag sometimes before. In this paper, the authors analyze two recently proposed RFID authentication schemes: randomized GPS and randomized hashed GPS scheme. They show both of them cannot provide backward privacy in Juels and Weis privacy model, which allows the adversary to know whether the reader authenticates the tag successfully or not. In addition, they present a new protocol, called Challenge-Hiding GPS, based on the Schnorr identification scheme.