A Systematic Review of Blockchain-Based Privacy-Preserving Reputation Systems for IoT Applications

With the growing popularity of the Internet of Things (IoT), billions of devices are anticipated to be deployed in various industries without establishing trust between them. In environments without pre-established trust, reputation systems provide an effective method of assessing the trustworthiness of IoT devices. There has been considerable literature on deploying reputation systems in industries that have not yet established trust among themselves. Therefore, the article reviews published studies on reputation systems for IoT applications to date, focusing on decentralised systems and decentralised systems using blockchain technology. These studies are evaluated regarding security (including integrity and privacy) and non-security requirements to highlight open research challenges. In alignment with this, an analysis and summary of the existing review studies on reputation systems for particular IoT applications are presented, demonstrating the need for a review article to consider all IoT applications and those that have not been explored. The IoT applications and sub-applications are described, and their problem statement, literature to date and research gap are comprehensively evaluated. Finally, the open research challenges concerning reputation systems are reviewed and addressed to provide the researcher with a road map of potential research directions.