# Formulating Cybersecurity Requirements for Autonomous Ships Using the SQUARE Methodology
## 4 Security Requirements for Autonomous Ships
### Derive Security Requirements
#### 4.2.4 Perform Risk Assessments  
According to onboard use and application of computer-based systems (IACS UR E22), autonomous navigation systems of autonomous ships can be classified as Category III with respect to the general classification of system capabilities or the degree of impact of malfunctions and the sensors and controllers below the degrees in Category III can be classified as Category II. In the attack tree shown in Figure 12, cyberthreats on autonomous ships can be classified as follows. Referring to the recommendation on incorporating cyber risk management into safety management systems (IACS No. 171), the threats were assessed considering their impact on autonomous ships and attacker accessibility. Reflecting the classification of IACS UR E22 according to system capabilities, the threats were classified on a scale of 1-3, as shown in Table 3.  
Figure 11: Cyber attack route.  
Figure 12: Autonomous ship attack tree.  
In this study, risk analysis and evaluation were performed by applying an informal approach among many risk analysis methodologies. The process adopted the ATR model [50], an asset-based method, to conduct a risk assessment with a focus on assets and threats, as shown in Table 4.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Category** & & **Potential Threat** \\ \hline \multirow{8}{*}{Systems in ship} & \(\bullet\) & Spoofing \\  & \(\bullet\) & Denial of service \\  & \(\bullet\) & Jamming \\  & \(\bullet\) & Obfuscation \\  & \(\bullet\) & Covert channels attacks \\  & \(\bullet\) & Steganography \\  & \(\bullet\) & Weak encryption \\  & \(\bullet\) & Authentication \\  & \(\bullet\) & Firmware update \\  & \(\bullet\) & Data corruption \\ \hline \multirow{8}{*}{AI} & \(\bullet\) & Poisoning attack \\  & \(\bullet\) & Evasion attack \\  & \(\bullet\) & Inversion attack \\  & \(\bullet\) & Model extraction attack \\  & \(\bullet\) & Buffer overflow \\  & \(\bullet\) & Brute forcing \\  & \(\bullet\) & Malware injection \\  & \(\bullet\) & Ship dataset attack \\  & \(\bullet\) & Sensor data attack \\  & \(\bullet\) & Artificial attack \\  & \(\bullet\) & Communication protocol attack \\ \hline \hline \end{tabular}
\end{table}
Table 2: Potential cyberthreat and attack scenario in autonomous ships.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & \multicolumn{3}{c}{**Threat List**} & \\ \cline{2-4}  & **Division 1** & **Division 2** & **Division 3** & **Value** \\ \hline
1 & & Ship dataset & Poisoning attack & 2 \\
2 & & attack & Backdoor attack & 2 \\
3 & & & Evasion attack & 3 \\
4 & AI model cyber & Sensor data & Spoofing & 3 \\
5 & attack & attack & Denial of service & 3 \\
6 & attack & & Jamming & 2 \\
7 & & Artificial neural & Buffer overflow & 3 \\
8 & & & brute forcing & 3 \\
9 & & & Malware injection & 2 \\ \hline
10 & & & Denial of service & 3 \\
11 & ICT cyber attack & Communication & Spoofing & 3 \\
12 & & protocol attack & Sniffing & 1 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Threat categories.