# Key Agreement and Authentication Protocols in the Internet of Things: A Survey
## 4 Discussion  
Many different protocols are available for use in IoT environments, with different characteristics, purposes and applications. As mentioned in this manuscript, we focused on protocols that fulfill the purposes of authentication, agreement, and agreement of the session key. The protocols may pursue one or more of these objectives during their operation. The overviewed protocols use cryptographic techniques to achieve their goals and secure communication. These protocols have been validated with various tools and methods for vulnerability to attacks and providing essential security features. In Table 2, we summarized the revised protocols in terms of the purpose they pursue. We have designated three types of protocols based on the analyzes performed. Here we can observe the need to create protocols primarily for user authentication. An essential aspect of communication is the reconciliation and agreement of session keys; hence, developing and applying this protocol is also key to securing communication. Table 3 provides a summary of the protocols discussed in terms of their uses and interoperability. We considered protocols targeted at specific solutions such as those intended for medicine and health, fog, edge, or cloud computing, and vehicular, drone, or industrial purposes. However, protocols that can be used in different resolutions (multidomain protocols) also play an essential role. In addition to multidomain solutions, many security protocols have been developed for solutions related to direct human safety, be it physical or environmental. First and foremost, it is about securing communications in medical environments where, on the one hand, we need to ensure patients 'data and privacy and, on the other hand, safeguard their health and life, as IoT devices are used to control patients' vital functions. Another important aspect will be the protocols for industrial solutions that also relate to securing people environmentally and physically. As in the case of medical solutions, we must secure both data sent in industrial networks and protect against attacks that could contribute to the incorrect operation of industrial devices and thus threaten the health and life of employees. Table 4 shows the attacks against which the described protocols for IoT are resistant. The table contains only those protocols for which the authors conducted formal and informal security evidence and indicated which attacks their proposed protocol is resistant to. In some papers (such as [81; 82; 91; 134; 136] or [137; 137; 138]) lists of attacks emerged. On the other hand, in other papers (such as [90; 109] or [112]), the authors only suggested that their protocols are resistant to typical attacks in IoT environments. The table contains a list of attacks and an annotation regarding the resistance of the tested protocol to attack. We only included those attacks that appear in a few papers. These attacks seemed once (e.g., Sybil attack or sinkhole attack) are included in the Others column. The flag + indicates that the authors have demonstrated that their proposed protocol is immune to attack. The flag - means that the protocol has not been verified to be vulnerable to attack. We have observed that the most frequently tested vulnerabilities in IoT environments are impersonation attacks, MITM attacks, and replay attacks. Most reviewed papers \begin{table}
\begin{tabular}{l l} \hline
**Protocol Type** & **References** \\ \hline Authentication protocol & [81; 82; 85; 90; 91; 96; 97; 98; 103; 106; 110; 122; 123; 124; 126; 127; 128; 129; 131; 134; 136; 140] \\ Authentication \& key & [100; 101; 102; 105; 109; 112; 116; 117; 121; 127; 135] \\ agreement protocol & [137; 138] \\ Key agreement protocol & [137; 138] \\ \hline \end{tabular}
\end{table} 
Table 2: The summary of protocol types. reported studies of proposed protocols for these attacks, indicating that they are among the most dangerous vulnerabilities.