Who stole my cheese?: Verifying intactness of anonymous RFID systems

Radio-Frequency Identification (RFID) technology has fostered many object monitoring applications. Along with this trend, a corresponding important problem is to verify the intactness of a set of objects using that of their attached tags. Existing solutions necessitate the knowledge of tag identifiers (IDs), sharing the intuition that verifying whether any tag is absent comes after knowing which tags are supposed to be present. Such solutions, however, can hardly live up to the recent vision of anonymous RFID systems that isolate tag IDs from protocols design for privacy concern. In this paper, we take the first leap toward verifying intactness of anonymous RFID systems. We first identify three critical solution requirements—deterministic verification, anonymity preservation, and scalability—for applications tolerating no absence. Without tag IDs as a priori, we propose a series of crypto-free, lightweight protocols that satisfy the requirements. The proposed protocols explore tag-cardinality difference or leverage Direct-Sequence Spread Spectrum enabled RFID. We validate their performance in terms of accuracy, privacy, and scalability through both analytical and simulation results. To cater for applications that tolerate losing some tagged objects, we further explore probabilistic intactness verification to trade tiny accuracy for boosted efficiency.