## 4 Taxonomy of Smart Healthcare Security Solutions
### System Level Attacks  
System-level attacks are those attacks where an attacker explicitly targets the system-level resources by discovering loopholes in the authentication schemes, authorization, and cryptographic key management infrastructure. In the smart healthcare sector, the patient's medical data have to be transmitted from various devices and services to reach their intended recipients. An attacker finds the system-level vulnerability to gain access to the patient's data and disrupts the performance of smart healthcare systems. Several researchers have proposed robust authentication schemes to overcome the aforementioned issues and reduce the impact of system-level attacks. For example, [PERSON] et al. in [94] proposed a three-stage authentication mechanism consisting of a smart card, password, and biometrics to ensure secure authentication between patients and healthcare providers. Then, they evaluated their proposed protocol using standard verification tools, i.e., real-or-random model, automated validation of internet security protocol, and Burrows-Abadi-Needham logic, wherein they outperform in terms of cost and secure functionalities compared to other baseline works. A two-stage authentication mechanism was proposed in [95] which involved hardware security, i.e., physical unclonable functions for IoT-based healthcare systems. Since the physical unclonable functions do not use cryptographic solutions, they can easily be integrated into the resource-constrained devices to offer lightweight authentication schemes. The proposed mechanism provides better computation time and offers robust security against system-level attacks in the smart healthcare ecosystem. Another system-level attack can be launched via privilege escalation techniques, where the attacker first carries out a reconnaissance of a victim's system to find hardware or software-related vulnerabilities that can be exploited at a later stage. [PERSON] et al. in [96] presented a novel static analysis framework that detects privilege escalation attacks in a unified extensible firmware interface (UEFI). The authors used a callback programming procedure to find malicious callable functions in the UEFI firmware. They collected 1148 UEFI binaries from different vendors, and discovered 36 privilege escalation vulnerabilities. Those vulnerabilities can cause random code execution and allow an attacker to modify the writing operation of the physical device.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & **Author** & **Year** & **Objective** & **4** & **5** & **6** & **7** & **8** & **Security Approach** & **OSI Layer** & **Secured** \\ \hline \multirow{4}{*}{Hardware-based attack solutions} & [79] & 2019 & To detect trojan attacks on medical hardware devices & Yes & No & No & Yes & No & Checkpoint assignment & Physical layer \\ \cline{2-8}  & & & To develop a secure data & & & & & & & \\  & & collection scheme for smart & Yes & No & No & Yes & Yes & Field programmable gate array (FPGA) & Physical layer, network layer \\ \cline{2-8}  & & & To improve the security & & & & & & IoT Hardware Platform & \\  & & performance of IoT devices & Yes & No & No & Yes & No & Security Advisor & Physical and \\  & & & performance of IoT devices & Yes & No & Yes & No & (IoT-HarfSecA) & network