Offline RFID Grouping Proofs with Trusted Timestamps

With the wide deployment of RFID applications, RFID security issues are drawing more and more attention. The RFID grouping proof aims to provide a verifiable evidence that two or more RFID tags were scanned simultaneously. It extends the yoking proof for two RFID tags, to prove the coexistence of a set of tags (e.g., some drugs can only be sold in the existence of a prescription). In many grouping proof scenarios, the time when the grouping proof was generated is critical to judge whether a transaction is legal or not, and the protocol usually should work in offline mode. Although lots of grouping proof protocols with various features have been proposed, they either work in online mode or have difficulties in generating a grouping proof with the precise transaction time in offline mode. Therefore, we propose a protocol to generate offline RFID grouping proofs with trusted timestamps, where the verifier can obtain the precise transaction time. As far as we know, it is the first practical offline grouping proof protocol that includes the precise transaction time. Properties, performance evaluation and security analysis of our design are also presented in this paper.