Generalized "Yoking-Proofs" for a Group of RFID Tags

Recently Ari Juels suggested a "yoking-proof" where a pair of radio-frequency identification (RFID) tags are both read within a specified time bound, and left open for future research the problem of generating a proof for larger groups of tags. We generalize his protocol by developing a proof which ensures that a group of tags is read within a certain time period. The tags generate such a proof even if the reader is untrusted. The proof is improbable to forge, and is verifiable off-line by a trusted verifier. Juels\´s problem formulation does not take privacy into account and the resulting protocol offers no privacy to the tags. We modify the problem statement to require the "yoking-proof" to maintain privacy, and we give a protocol for this new anonymous yoking problem, along with suggestions for speed ups