Analysis and Optimization of Hierarchical ID-Based Encryption for MQTT

With the widespread adoption of Internet of Things (IoT), the number of IoT devices has increased significantly. To facilitate efficient data transmission on these devices, researchers have proposed numerous communication protocols. Among them, the Message Queueing Telemetry Transport (MQTT) protocol based on the publish/subscribe model is widely used. However, by default, the data transmissions with MQTT are plaintext. The MQTT specification recommends using TLS protocol to encrypt the MQTT packet. Due to the high computation cost of TLS, Fan et al. [1] propose a data protection scheme based on hierarchical ID-based encryption utilizing the topic hierarchy in MQTT. In this paper, we conduct a detailed analysis of their subscription algorithm with a multi-level wildcard and identify a security issue related to the leakage of the secret key in their scheme. Also, we present three possible solutions to address this problem.