Ad hoc subgroup proofs for RFID

In many RFID applications it is necessary to be able to identify the presence of (all) the tags of a predefined group, e.g., to establish that all components of a kit are present. If the interrogation is offline, by RFID readers that do not share any secret keys with the tags, then a record of simultaneous presence, or a grouping proof, has to be generated by the tags themselves. This type of proof is typically obtained by assigning to each tag in the group a unique group identifier. In certain situations, however, the entire group may not be present, and it may be sufficient that a (an ad hoc) subgroup proof is generated. In this paper we consider ad hoc subgroup proofs. We first describe a generic ad hoc subgroup proof by extending a previously proposed grouping proof to an ad hoc setting. We then propose a novel ad hoc subgroup proof for RFID that supports privacy (unlinkability).