A Comprehensive Review for 4-D Trust Management in Distributed IoT

Compared with other security technologies of the Internet of Things (IoT), trust management (TM) can accommodate sudden or unpredictable changes brought about by ethical and moral standards. First of all, this article introduces the basic contents of TM, including objectives, overall architecture, threat model, related indicators, application scenarios, and so on. Then, this article develops four dimensions: 1) trust-related data (TRD); 2) trust evaluation mechanisms; 3) trust propagation mechanisms (TPMs); and 4) trust influence mechanisms (TIMs), and describes the main contents. There are 4 kinds of TRD and 12 kinds of trust evaluation mechanisms, including trust evaluation mechanisms meeting reinforcement learning. There are five kinds of TPMs and six kinds of TIMs. Based on four dimensions, the existing TM is classified and summarized. Finally, this article gives the current research challenges and future research directions in each dimension. In addition, the modeling process based on 4-D TM is given in the conclusion. In this article, the TM model is based on the mass points in the 4-D space, and the mapping on each dimension is specific data or methods, which can be selected. If the specific content of each dimension is selected, the TM model will run according to a specific process in a specific IoT environment. The 4-D trust management model helps to select more appropriate data or methods to effectively adapt to the dynamic and complex environment of the IoT.