WhisperMQTT: Lightweight Secure Communication Scheme for Subscription-Heavy MQTT Network

The Message Queuing Telemetry Transport (MQTT) protocol is widely used for communication in machine-to-machine (M2M) and Internet of Things (IoT) systems due to its lightweight publish-subscribe model. Although MQTT can be secured with Transport Layer Security (TLS), this introduces significant computational overhead on the message broker. We demonstrate that this overhead becomes unnecessarily high in subscription-heavy networks, where a single message must be encrypted individually for each subscriber. To address this issue, we present WHISPERMQTT, a solution designed to optimize the encryption process in MQTT brokers. Our approach utilizes both TLS and non-TLS connections with subscribers: the TLS channel is used to securely distribute a per-topic decryption key, while the encrypted payload is transmitted over the non-TLS connection. This allows the broker to encrypt each topic message only once, irrespective of the number of subscribers, which reduces processing overhead and enhances both latency and throughput. Importantly, WHISPERMQTT integrates seamlessly with the MQTT protocol and applications without requiring any modifications.