Evaluating the cost of beyond AES-128 LoRaWAN security

LoRaWAN is one of the most popular Internet of Things radio communication technologies since it allows data to be transmitted over long distances with low power consumption on unlicensed ISM bands. Devices used with LoRaWAN are often constrained for reasons of manufacturing cost and to save energy as they are most often battery-powered. As a consequence, security mechanisms chosen for such devices must be lightweight. The LoRaWAN standard relies on AES-128 for encryption and authentication, using a pre-shared key. With the increasing amount of computational power at hand and the advent of quantum cryptography, the use of short AES keys without renewal for long periods of time is a potential weakness. However, using longer keys in LoRaWAN impacts end devices in terms of processing time and energy consumption. It might also require adaptations in the protocol design. This paper investigates the cost of using different AES key sizes with different payload sizes on an off-the-shelf LoRaWAN platform. Our results show that costs in terms of delay and energy consumption are moderate and using longer key sizes is a practical solution to increase the security of LoRaWAN.