# A Trust-Influenced Smart Grid: A Survey and a Proposal
## 1 Introduction  
The Smart Grid is the transformation of the traditional grid which can be combined with cyber devices to automate monitoring and control as well as include a two-way communication between systems [1]. The Smart Grid's performance, just like that of the traditional grid, is centred on factors such as distribution, transmission, and generation. The coupling of the traditional power grid's physical components and the cyber infrastructure has made the creation and continuous improvement of the Smart Grid possible. The diverse nature of the Smart Grid introduces varying applications and the integration of components such as electric vehicles, renewable energy resources, and variants of distributed power generators. Smart Grid has also introduced and improved vendor-independent standards that devices must conform to, thus allowing the seamless operation and integration of these devices into the Smart Grid. Unfortunately, the cyber infrastructure's integration into the power grid increases the attack vector of the Smart Grid, thereby making the security of the Smart Grid ofparamount importance. In response, research has been undertaken under varying topics such as encryption [2], generation and management of cryptographic keys [3], privacy [4], risk assessment [5], and trust. Trust within the Smart Grid is important for determining whether an action, transaction, or communication is malicious or not. In the case of the notorious Stuxnet [6], there is the possibility that trust could have been implemented in devices to ascertain the legitimacy of malicious commands before responses or actions are taken on those commands. We also observed that research on trust has not received the considerable attention that it deserves within the Smart Grid even though it abounds in other research areas such as E-commerce. Furthermore, other branches of security within the Smart Grid have largely received more contributions than trust. As of the time of writing this paper, no study assessing trust within the Smart Grid exists. As of the time of this study, we noticed that there were limited trust models that detected operational faults within the substation. However, these models could neither determine whether the faults were malicious or not, nor detect obvious or stealthy malicious attacks within the substation. Such attacks were predominant within advanced persistent threats (APTs). The contributions of this study are as follows:  
* We present a mathematical formalization of trust within the context of Smart Grid devices. * We categorize the existing trust-based literature within the Smart Grid under the NIST conceptual domains and priority areas, multi-agent systems, and the derived trust formalization. * We present a proposed novel substation-based trust model and implement a Modbus variation to detect final-phase attacks. We believe other protocol variants of the trust model can be created and developing these will be addressed in future work. * The variation is tested against two publicly available Modbus datasets (EPM and ATENA H2020) under three kinds of tests, namely external, internal, and internal with IP-MAC blocking. * The tests were performed from a Modbus server's point of view and a Modbus client's point of view. * All attacks were detected and the behaviour of attacks was revealed based on their impact on the trust model's components. In this paper, we provide a background on the priority areas and conceptual domains of the Smart Grid as described by the National Institute of Standards and Technology (NIST) in Sections 2 and 3. We then present a background on trust, its definitions, and trust-related attacks in Section 4. We categorize existing literature from Sections 5-8. We present a proposed trust model and its Modbus variation from Sections 9-11. Implementation and results are presented in Sections 12 and 13, respectively. We provide our conclusions and future work in Sections 14 and 15. We also included a table of notations in Appendix A to be used as reference for the equations in the paper.