# Blockchain-based Multifactor Authentication for Future 6G Cellular Networks: A Systematic Review
## 7 Observations  
### Recent Trends and Observations  
Based on the reviewed articles in this study, we observe that the MFA scheme provides an immersed level of improvement to secure sensitive data by preventing the systems from security threats. Figure 6 depicts the researchers' percentage of usage of different MFA enable mechanisms based on research studies. Almost 30% of the MFA methods were hardware tokens to highlight their importance. The soft token and OTP based on the SMS were the next important MFA enable mechanism, with almost 23% of studies employing it. While the hardware-based OTP and the authenticator applications were the less popular mechanism as adopted by almost 12% of studies only. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Study**} & \multicolumn{2}{c}{**Technologies Mentioned**} & \multirow{2}{*}{**Advantage/Contribution**} & \multirow{2}{*}{**Disadvantage/Gap**} \\ \cline{2-2} \cline{5-5}  & **MFA** & **BC** & **3/4/5G** & & \\ \hline \multirow{3}{*}{[98]} & \multirow{3}{*}{✓} & \multirow{3}{*}{✓} & Multiple server technologies are used to ensure & \multicolumn{2}{c}{Technique still poses a} \\  & & & that performance is quick and transparent. & \multicolumn{2}{c}{} \\ \cline{5-5}  & & & & card authentication. & \\ \hline \multirow{3}{*}{[97]} & \multirow{3}{*}{✓} & \multirow{3}{*}{✓} & An adaptable and decomposable 3-factor & \multicolumn{2}{c}{} \\  & & & authentication system that can be applied & \multicolumn{2}{c}{} \\ \cline{5-5}  & & & simultaneously to ensure efficiency and speed. & \multicolumn{2}{c}{} \\ \hline \multirow{3}{*}{[32]} & \multirow{3}{*}{✓} & \multirow{3}{*}{✓} & Hydro Raindrop multifactor authentication & \multicolumn{2}{c}{} \\  & & & technology to conduct 2 FA for WordPress. & \multicolumn{2}{c}{} \\ \hline \multirow{3}{*}{[10]} & \multirow{3}{*}{✓} & \multirow{3}{*}{✓} & A lack of support for batch & \multicolumn{2}{c}{} \\  & & & BPAS for ensuring accuracy as well as trust in & \multicolumn{2}{c}{} \\ \cline{5-5}  & & & the systems. & \multicolumn{2}{c}{} \\ \cline{5-5}  & & & & the resource consumption. & \multicolumn{2}{c}{} \\ \hline \multirow{3}{*}{[15]} & \multirow{3}{*}{✓} & \multirow{3}{*}{✓} & Embedded Digital Signature-based MFA suitable & \multicolumn{2}{c}{} \\  & & & technique for countering the adversarial attacks. & \multicolumn{2}{c}{} \\ \hline \multirow{3}{*}{[8]} & \multirow{3}{*}{✓} & \multirow{3}{*}{✓} & More security to the authentication process as & This system was claimed to be safer & \multicolumn{2}{c}{} \\  & & & compared to SMS-based authentication protocols. & \multicolumn{2}{c}{} \\ \cline{5-5}  & & & & efficient in terms of time efficiency. & \multicolumn{2}{c}{} \\ \hline \multirow{3}{*}{[11]} & \multirow{3}{*}{✓} & \multirow{3}{*}{✓} & \multirow{3}{*}{✓} & Flexible, secure, and reliable authentication. & The overheads of blockchain use, \multicolumn{2}{c}{} \\ \cline{5-5}  & & & & however, were high. & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._  
Figure 6: Trends in different authentication types to enable MFA. Figure 7 highlights the usage of different security mechanisms for the 3G, 4G, or 5G communication technologies based on the reviewed articles. It is also observed that 67% of the reviewed papers focused on the MFA-based schemes only to provide security to different networks considering the 3G, 4G, or 5G communication networks. Additionally, only 33% of studies focused on integrating BC along with the MFA authentication schemes for securing communication networks. We observed that mostly BC-based MFA studies were conducted from 2019 onward, which is one of the main reasons for its lower popularity compared to MFA schemes. This observation also highlights that BC-based MFA schemes are less explored, and there is more room for research in this emerging field. It can be observed that most of the studies conducted to date about the BC integration with the MFA are focused on the 5G networks.