# A Survey on Cyber Risk Management for the Internet of Things
## 4 Cyber Risk Assessment for IoT Survey Results
### IoT Cyber Risk Calculation
#### 4.2.2 Use of Risk Matrices  
A risk matrix is a well-known method used to describe the probability and impact associated with an attack [90] which can be used to produce a risk value in a qualitative or semi-quantitative way. [PERSON] et al. [75] analyses IoT risk using a matrix that describes risk probability and impact, resulting in a qualitative result based on the risk response: avoidance, mitigation, transference, and acceptance. Meanwhile, [PERSON] et al. [71] represent the impact at a IoT network's node using an impact matrix, with this then being integrated to show the cumulative impact for an attack vector. In contrast, [PERSON] et al. [53; 54] utilise an adjacency matrix to indicate IoT hot spots in a network and how they are connected within the system In addition, to define IoT risk, [PERSON] et al. [53] finds the cumulative IoT risk of an attack pathway and represents it as a threat score matrix, mapping the nodes and links of a pathway with the calculated score. [PERSON] et al. [74] use risk matrices as part of a three-tiered scoring system based on IoT threat characteristics that affect impact severity and probability of an attack occurring. Upon the creation of a risk matrix, different colours are used to represent the various levels of risk from very low to very high, allowing for risks to be prioritised, with the authors suggesting the modification of a risk matrix to prioritise impact in cases were an IoT attack could threaten life. [PERSON] and [PERSON] [64] express the probability and impact of IoT attacks using a measurement criterion of low, medium, and high, which is then utilised in a risk matrix to evaluate different attack scenarios. For example, a low-impact and probable IoT attack scenario would be considered low risk. The risk matrix provides a basic calculation to express the risk value associated with each attack scenario, making it easier to identify and prioritise potential risks. Unlike prior papers, the Common Vulnerability Scoring System is used by [PERSON] and [PERSON] [42] to formulate a threat score matrix for smart thermostat components using STRIDE, where each STRIDE attack group is mapped to various system components (e.g., firmware and credentials) by threat scores (such as high and critical levels of threats). [PERSON] et al. [49] use a STRIDE-per-element matrix that shows attacks based on STRIDE mapped to system components. However, the STRIDE-per-Element matrix often excludes threats that were relevant, such as all data flows being affected by spoofing attacks rather than others like man-in-the-middle attacks. [PERSON] et al. [75] have adopted a project management approach to assess IoT risks, which includes a three-step process for formulating the risk assessment process. The first step involves gathering risk specifications through a literature survey. By reviewing existing literature, the authors can identify potential risks and develop a better understanding of the overall risk landscape for IoT systems. Upon finding 28 risk factors, these are analysed using and risk matrix, mapping the risk probability and impact of risks, classifying them based on risk avoidance, risk mitigation, risk transference, and risk acceptance. Finally, is the risk evaluation phase which evaluates proposed countermeasures and quantifies the risks using a risk formula. The formula first finds a risk value based on the approximated asset value, value of threat, and value of vulnerability, with the second using impact, probability, and value of vulnerability. Within [PERSON] et al. [51] proposed a risk assessment model that considers hardening processes, which is aimed at minimising the attack surface. The authors use compliance class scores based on CIA impact, For example, class one reflects a limited impact on the IoT system where a low potential impact on confidentiality, a medium potential impact on integrity, and a medium potential impact on availability.