CRAM: Robust Medium Access Control for LPWAN using Cryptographic Frequency Hopping

Low power wide area networks (LPWANs) are being applied in many Internet of Things applications around the globe. These technologies offer economic coverage of wide areas, while retaining low power operation. LoRaWAN is a key technology in this space, with a world-wide presence and millions of devices deployed in the field. Despite this early success, recent research has shown that LoRa performs poorly in dense deployments with a high degree of contention. Furthermore, LoRa is not robust against selective jamming attacks. In this paper, we propose CRAM: a cryptographic frequency hopping MAC protocol designed for the LoRa physical layer that reduces contention by fairly exploiting all available frequency space, while making it significantly more difficult to perform selective jamming. Our evaluation shows that CRAM significantly reduces contention, thereby dramatically increasing scalability and reliability in comparison to the standard LoRa protocol.