Grouping-Proof-Distance-Bounding Protocols: Keep All Your Friends Close

The use of wireless communications has had tremendous expansion and has led to the development of wearable devices with limited resources. Often, to gain access to services/places, proving the physical proximity of a single device, may not be enough. Multiple wearable devices linked to function as a team may provide stronger guarantees on accurate authentication. Although distance-bounding (DB) protocols provide a reliable way to prove the physical proximity of a device and grouping-proof (GP) protocols can be employed to prove the presence of multiple provers, proving that multiple devices are present and in close proximity to a verifier is more challenging. In this letter, we introduce a new concept that extends traditional DB protocols to a multi-prover setting and we propose the first GPDB protocol that provides not only a proof of the presence of multiple provers at the same time but also assurance regarding the physical proximity of the provers, requiring limited computational effort. Furthermore, we discuss the effectiveness of this protocol, considering the main threats in DB and GP protocols.