# A Trust-Influenced Smart Grid: A Survey and a Proposal
## 8 MASs with Trust in the Smart Grid
### Discussion  
In stark contrast to Section 5, MAS-based trust within the AMI and network communication priority areas do not exist as shown in Table 5. Furthermore, energy storage, electric transportation, and WASA priority areas are still uncharted territories when it comes to trust. There are only three papers each for DER and distribution grid and only two for demand response and consumer energy efficiency areas. Clearly, this shows that a lot of work is required on trust in MAS-based environments in the Smart Grid. Table 6 shows that the generation, customer and service provider domains have yet to be explored while the markets domain only has two papers. Three papers were focused on the the transmission, distribution, and operation domains, while only one was focused on the operations domain and only two focused on only the distribution domain. Only one paper includes the risk component in its trust model, as shown in Table 7. The knowledge component of most of papers did not include previous transactions or states; therefore, trust was computed based on the values of parameters that were provided for computation. There were three papers that exclusively focused on direct trust, and one paper focused on indirect trust. Five papers focused on both types of trust. communication that is received has to be computed to calculate trust. Furthermore, a history of communications is required to be stored to be used as a reference to compute trust. Concerning the formulation of trust in Section 4.1, trust among IEDs (and also SCADA) can be seen as a tuple with some modifications, as shown in (8). \[T_{ij}=f(m_{ij},d_{i},d_{j},r_{ij},h_{ij}) \tag{8}\]  
\(m_{ij}\) is the message being analyzed before it can be trusted and accepted, \(d_{i}\) is the agent device, \(d_{j}\) is the subject device, \(r_{ij}\) is the risk involved should the message be accepted or trusted, and \(h_{ij}\) is the history of communication between \(d_{i}\) and \(d_{j}\). A simple conceptual algorithm is presented in Algorithm 1 where \(d_{i}\) receives \(m_{ij}\) from \(d_{j}\) and computes \(T_{ij}\) based on \(m_{ij}\). If \(T_{ij}\) equals or exceeds the threshold value, \(m_{ij}\) is received and acted upon, otherwise it is dropped and an alert is raised. It must be noted that trust can be scaled on a continuum such that certain actions are taken when certain thresholds on that scale are exceeded [90]. Actions can range by sending warnings, raising alarms or in the worst case scenario, refuse to communicate with a non-trusted device. ```
Receive \(m_{ij}\)  Compute \(T_{ij}=f(m_{ij},d_{i},d_{j},r_{ij},h_{ij})\) if\(T_{ij}\geq T_{threshold}\)then  Accept \(m_{ij}\) else  Drop \(m_{ij}\)  Raise alarm endif
```  
**Algorithm 1** Pseudo-algorithm for trust computation for agent device  
In Figure 5, we present a proposed trust model that can be implemented in a substation environment. We define consequence as the measure of damaging impact an action has on a substation. Consequence represents the risk involved when a current action/message is taken within the substation and requires some parameters from familiarity as input. Consequence requires knowing the state of the substation (environment state) and the dependencies (criticality) within the substation to calculate the risk or consequence of the action to be undertaken. We define familiarity as a measure of the consistency of actions/messages of different types between devices. Familiarity, in this situation, maps to the history of communication or existing knowledge in the trust formalization presented to date. According to [PERSON] [91] and [PERSON] et al. [92] factors that influence familiarity are exposure intensity, exposure frequency, and similar exposure. Exposure frequency is defined as the frequency with which messages/actions are exposed to the devices. Figure 5: Proposed trust model for substation. Exposure intensity is defined as the length of time in which the messages/actions are exposed to the devices.