## 2 Materials and Methods
### Background and Related Work
#### 2.1.2 Threat Model
Additionally, it is observed that each of the five categories is evaluated from 0 to 3, where zero is the absence of risk and three is the highest value (a more detailed quantification can be seen in the Table 4) since using this table helps reduce the subjectivity inherent to DREAD, which has been considered a drawback of this method. In general, by analyzing the Table 5, it is noted that the greatest challenges are associated with the LPWAN(8) link attack surfaces and the data server(4), using CVSS prioritization as a basis. In both cases, data integrity is the central issue. However, individually, the threats that had the highest priority were \"message tampering\"(3) and \"unauthorized access\"(3). The first one (v09) can occur in any service that communicates through LPWAN in MFA_R, but it has greater relevance when publishing data in DataServ. The second one (v11) is a big problem at any point in the MFA_R workflow as its event invalidates its entire purpose. Subsequently, one can consider these two surfaces and threats as points of great interest in the design and evaluation of solutions in MFA_R. In the last part, the countermeasures(3) are presented as the implementation of the security requirements arising from the threat analysis done previously. As a result, the \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \# & **Threat** & **D** & **R** & **E** & **A** & **D** & **Total** & **Risk** \\ \hline v01 & information disclosure & 3 & 0 & 0 & 1 & 2 & 6 & 1.2 \\ v02 & leakage & 3 & 1 & 0 & 1 & 2 & 7 & 1.4 \\ v03 & DoS & 3 & 2 & 0 & 2 & 2 & 9 & 1.8 \\ v04 & device impersonation & 1 & 2 & 1 & 1 & 1 & 7 & 1.4 \\ v05 & brute force attack & 1 & 3 & 3 & 1 & 2 & 10 & 2 \\ v06 & device impersonation & 1 & 2 & 1 & 1 & 1 & 7 & 1.4 \\ v07 & tampering data & 2 & 2 & 2 & 3 & 2 & 11 & 2.2 \\ v08 & information leakage & 2 & 0 & 0 & 1 & 0 & 4 & 0.8 \\ v09 & message tampering & 1 & 2 & 2 & 1 & 1 & 8 & 1.6 \\ v10 & message fabrication & 1 & 2 & 2 & 1 & 1 & 8 & 1.6 \\ v11 & unauthorized access & 3 & 2 & 2 & 2 & 1 & 11 & 2.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: DREAD risk evaluation—this artifact presents quantitative risk assessment through the DREAD tool. From the left is the vulnerability identification column; its brief description; the five evaluation categories of this TMM; the total sum of the evaluations; and the averages of the evaluations, that is, the risk. main threats were chosen based on Table 5. Since these challenges were translated into security requirements for MFA_R, which resulted in the four requirements shown in Table 6, correspondingly, these aspects are key points of the mechanism. They attempt to literally translate the points where the mechanism cannot fail during the communication between all the components. Although translated into only four aspects, the requirements can map several vulnerabilities combined (Table 6--column 3) and guarantee that an eventual security breach is discovered. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \# & **Aspects** & **Threats** \\ \hline a01 & all data publishing must be done only by authenticated devices & v03, v04, v07, v09, v11 \\ a02 & credential generation should be identified & v04, v05, v06, v11 \\  & and mitigated & v04, v05, v06, v11 \\ a03 & credential theft should be identified & v04, v06, v11 \\ a04 & publication of random data should be & v10 \\  & identified and mitigated & & \\ \hline — & out of scope & v01, v02, v08 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Security aspects promoted by the MFA_R mechanism—the aspects represent key points in ensuring the security of the mechanism and combined cover a wide range of attacks.