Radio Frequency Identification (RFID) is a challenging wireless technology with a great potential for supporting supply and inventory management. In this chapter the authors consider a particular application in which a group of tagged items are scanned to generate a record of simultaneous presence called a grouping-proof. Grouping-proofs can be used, for instance, to guarantee that drugs are shipped (or dispensed) accompanied by their corresponding information leaflets, to couple the user’s electronic passport with his/her bags, to recognize the presence of groups of individuals and/or equipment and more generally to support the security of supply and inventory systems. Although it is straightforward to design solutions when the verifier is online since it is sufficient for individual tags to authenticate themselves to the verifier, interesting security engineering challenges arise when the trusted server (or verifier) is not online during the scan activity. So, the field of grouping-proofs is very active, and many works have been published so far. This chapter details the setting for RFID grouping-proofs and discuss the threat model for such applications. The authors analyze some of the grouping-proofs proposed in the literature describing their advantages and disadvantages. Then, general guidelines for designing secure grouping-proofs are proposed. Finally, some examples of grouping-proofs that are provably secure in a strong security framework are presented.
