## 8 IoMT Security Model
### Blockchain Models  
[PERSON] et al. [76] proposed a secure scheme which they named as \"MedSBA\". It includes the application of attribute-based encryption methods combined with blockchain technology for sharing and storing medical data among patients, hospitals, and other stakeholders. This scheme applies two types of attribute-based encryptions, KP-ABE (Key-Policy Attribute-Based Encryption) and CP-ABE (Ciphertext-Policy Attribute-Based Encryption), to control patients' access to their own medical data. It also includes two PBFT (Practical Byzantine Fault Tolerance) consensus-based private blockchains in two forms: permissionless and permissioned. The former is used to distribute public medical information and the structure for the authorized access to medical data, and the latter is to set the information of key and storage places on the cloud-storing systems. The system's functionality was proven using BAN (Burrows-Abadi-Needham) logic, while the security was proven using formal design. Simulating MedSBAs with OPNET software demonstrates the system's efficiency in terms of computing complexity and storage. However, the system did not facilitate the exchange of cryptocurrency for data sharing between data-consumer organizations and individuals. \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Device Type** & **Implantable** & **Internet of** & & \\
**Medical Devices** & **Wearable Devices** & **Ambient Devices** & **Stationary Devices** \\ \hline
**Device Location** & In human tissues & On the human body & Close to the human body & Inside treatment rooms and hospitals \\ \hline  & & EEG and ECG, fall & & \\  & & detection band, & Motion sensors, & \\  & & blood pressure & pressure sensors, & \\  & Pacemaker, deep & monitors, smart & vibration sensors, & (such as, MRId, CT \\
**Examples of Devices** & & brain implants, & watches, & gyroscope sensors, & scanners, and \\  & & insulin pump & accelerating & daylight sensors, & X-rays) and surgical \\  & & sensors, respiratory & and pressure & devices \\  & & rate sensors, fitness & sensors & \\  & & & trackers & \\ \hline
**Perception Layer** & **Side channel** & ✓ & ✓ & N/A & ✓ \\
**Potential** & **Tag cloning** & N/A & ✓ & N/A & N/A \\
**Attacks/Difficulty** & **Tampering devices** & N/A & ✓ & ✓ \\  & **Sensor tracking** & ✓ & ✓ & N/A & N/A \\ \hline  & **Eavesdropping** & ✓ & ✓ & ✓ \\
**Network Layer** & **Replay** & ✓ & ✓ & ✓ \\
**Potential** & **Man-in-the-middle** & ✓ & ✓ & ✓ \\
**Attacks/Difficulty** & **Rogue access** & ✓ & ✓ & N/A \\  & **DoS** & ✓ & ✓ & ✓ \\  & **Sinkhole** & ✓ & ✓ & N/A \\ \hline
**Application Layer** & **SQL injection** & ✓ & ✓ & ✓ \\
**Potential** & **Account hijacking** & ✓ & ✓ & ✓ \\
**Attacks/Difficulty** & **Ransomware** & ✓ & ✓ & ✓ \\  & **Brute force** & ✓ & ✓ & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 4: IoMT device categories, their locations, examples for each category, and potential attacks. [PERSON] et al. [77] designed an authentication key agreement scheme termed as \"BAKMP-IoMT\", based on blockchain for the IoMT environment. It provides secure key management for cloud servers, personal servers, and medical implantable devices. Furthermore, the system enables secure access to critical healthcare data and guarantees that only authorized individuals have access to it. Legitimate people can also securely access healthcare data via cloud servers. This is accomplished by keeping all sensitive healthcare information in a blockchain that is managed by cloud servers. To demonstrate the system's ability to withstand many types of hypothetical attacks, a comprehensive formal security study has been performed using a widely recognized automated tool, AVISPA (automated validation of Internet security protocols and applications), as well as formal and informal security analyses. BAKMP-IoMT is compared with other existing schemes, and it also performs better in terms of security and functionality, lower communication and communication costs for authentication, and key management phases compared to other schemes.