TLS Beyond the Broker: Enforcing Fine-Grained Security and Trust in Publish/Subscribe Environments for IoT

Message queuing brokers are a fundamental building block of the Internet of Things, commonly used to store and forward messages from publishing clients to subscribing clients. Often a single trusted broker offers secured (e.g. TLS) and unsecured connections but relays messages regardless of their inbound and outbound protection. Such mixed mode is facilitated for the sake of efficiency since TLS is quite a burden for MQTT implementations on class-0 IoT devices.