Increasing the pervasiveness of the IoT: fog computing coupled with pub&sub and security

People are increasingly surrounded by a connected world, where they can gather and share information everywhere, at anytime, and by means of a variety of devices, belonging to the so-called Internet of Things (IoT) network. IoT technologies and applications are spreading in different scenarios, ranging from every-day life activities to business ones. The presence of a huge amount of data, continuously transmitted over the network, brings relevant issues in terms of scalability. Hence, a proper network infrastructure must be put in action, in order to efficiently manage the information. A middleware layer could be a potential solution for overcoming such an issue, and to cope with interoperability. In literature, many architectures have been proposed in the last years, but little attention has been paid to how to decentralize as much as possible all the network's components and tasks, in order to cover a wider area, avoiding single points of failure, while guaranteeing efficiency. Moreover, the interest of different stakeholders is not adequately considered yet. In this sense, fog computing represents a viable approach, which is adopted in this paper for the realization of a highly distributed and security-aware IoT middleware, aimed at operating without the need of a central coordinating unit and at allowing the participation of multiple stakeholders in the same IoT infrastructure. The proposed solution exploits the functionalities provided by the MQTT protocol, and its potentialities, besides the architectural features, are evaluated by means of a simple yet real test-bed, in terms of computing effort and latency