Date Added: Sep 2009
How can a RFID (Radio Frequency Identification Devices) system prove that two or more RFID tags are in the same location? Previous researchers have proposed yoking-proof and grouping-proof techniques to address this problem - and when these turned out to be vulnerable to replay attacks, a new existence-proof technique was proposed. The paper critiques this class of existence-proofs and show it has three problems: a race condition when multiple readers are present; a race condition when multiple tags are present; and a problem determining the number of tags. The paper presents two new proof techniques, a secure timestamp proof (secTS-proof) and a timestamp-chaining proof (chaining-proof) that avoids replay attacks and solve problems in previously proposed techniques.