## 5 Review Findings
Figure 22: Article distribution based on authentication key. There are many ways to evaluate the proposed authentication schemes for performance parameters. Many researchers implemented different schemes through programming and prototyping [28, 112]. Moreover, the research experiments can be conducted using performance testing of the amount of memory required, the number of steps for authentication, and the amount of CPU time required. By reviewing the literature, the evaluation process is mainly based on scheme simulation. The popular simulation tools are shown in Figure 24.  
One of the popular tools for evaluating authentication schemes in IoMT environments is called Network Simulator (NS). It is useful for education and research since it is based on discrete-event simulation [24, 31, 46, 68, 75, 81, 95, 124, 125]. [PERSON] [56], [PERSON], and [PERSON] [83] took advantage of the CloudSim tool to evaluate their proposed authentication schemes. CloudSim is a modeling and simulation framework used to test cloud infrastructure and services that are not only used for education and research. MATLAB Simulator is a model-based tool where a researcher needs to design a mathematical model for the proposed authentication scheme [76, 85, 126]. It is a powerful tool since it generates codes automatically, depending on the predefined model. [PERSON] et al. [96] used the Elastic Compute Service (ECS) host offered by the Alibaba Cloud platform. The Alibaba platform helped them to simulate their proposed cloud server and fog nodes authentication method in an IoMT system. [PERSON] et al. [43] used Remix IDE as a powerful tool to simulate their smart contracts through the Solidity programming language. [PERSON] et al. [42] demonstrated the performance of their proposed authentication scheme through the OPNET simulator network tool. Using one simulation tool rather than the other is related to the researcher's preferences and background experience with a particular tool. Therefore, the distribution frequency of articles shows the spread of usage percentages among different tools. However, the network simulator records the highest percentage with 16%. Figure 25 shows the article distribution based on the use of evaluation tools. Figure 23: Article distribution based on cryptography approach. Figure 24: Performance evaluation tools for authentication schemes. The evaluation of authentication schemes for IoMT is conducted primarily for three performance parameters: computation, communication, and storage overhead. The evaluation of computation overhead relies on the extent to which authentication schemes are lightweight in terms of time as related to any resource-constrained IoMT environment. Therefore, less time is required to achieve the authentication process, which implies less cost and a more lightweight authentication scheme. To enhance the authentication scheme for communication overhead, the data pass among entities must be as least as possible. The storage overhead refers to the memory needed to accomplish the authentication process. Storage overhead is a vital parameter to evaluate authentication schemes because of the limited storage capacity of the IoMT devices. Table 4 briefly compares computation, communication, and storage overhead among the recently proposed IoMT authentication schemes. The values of Table 4 indicate the evaluation results on the terminal side. Many techniques and tools are available for validating the security properties of authentication schemes. The Automated Validation of Security Applications and Protocols tool (AVISPA) is widely employed for such a purpose. It is based on an expressive formal language, and many back-ends, to automatically analyze application and protocol security properties [31]. Cyther is another verification tool for testing the sensitivity of Internet protocols to security properties. It is designed as a framework to model adversaries for analyzing a protocol's security [130]. It simulates a basic Dolev-Yao threat model, and also more powerful adversary models [24].