# Blockchain-based Multifactor Authentication for Future 6G Cellular Networks: A Systematic Review
## 4 Multifactor Authentication
### Use of MFA  
MFA is a development that has been aimed at increasing the level of security of the authorized access to personal information, resources, and important data. In accordance with the Commission Implementing Regulation (E.U.) 2015/1502 [35], a secure and strong authentication process is based on at least two authorization factors. The MFA uses the shortcomings of the single and double authentication and the traditional I.D. and password mechanisms, and the developers use these to develop a more secure method. The main problem with less sturdy mechanisms of authentication is that the users become susceptible to hacking, security breaches by compromising the passwords and, in the case of financial transactions, costing large sums of money to the users [16]. Brute force attacks are also an actual hazard, as hackers and other bad actors can use the automated passwords, thereby cracking the safety protocols by trial and error until they arise on the correct sequence. However, some accounts and application developers enable locks after multiple incorrect password attempts, helping the organizations track and protect their users. Thus, one of the primary uses of the MFA is its characteristic of reducing the security risks [30; 36; 37; 38; 39; 40]. There are different ways through which the MFA is enabled. Table 3 illustrates the methods through which MFA is enabled.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**MFA Type** & & **Process** & **Pros** & & **Cons** \\ \hline \multirow{8}{*}{Hardware OTP} & - & A one-time code is & & & \\  & generated using the & & & & \\  & cryptographic keys stored & & & - & A Weak user experience, due \\  & & inside devices & & & to which the users are limited \\  & - & This key is also accessed by & - & Easy to adopt & & in the operation of tasks, \\  & & the server, which generates & - & Gives the OTP & & which is not compatible with \\  & & a similar OTP to confirm & - & Available widely & & technological and \\  & [37; 38] & the OTP against the values & - & Email signing & & lifestyle factors. \\  & & provided by the user. & & and encryption & - & High costs for operation \\  & - & Interfaces may include & - & Customization possible. & & and maintenance. \\  & - & token representation of & & - & Only works on compatible \\  & & OTP on screen /device & & & infrastructures. \\  & & requiring user to enter PIN & & & \\  & & for accessing it. & & & \\ \hline \multirow{8}{*}{Authenticator Applications} & - & Different applications such & & - & Needs user to switch between the applications to \\  & & as google authenticator and & & & authenticate the identity, user, \\  & & Microsoft authenticator. & & & and transaction losses with \\ \cline{1-1}  & - & These applications are mere & - & Once set up in the & \\ \cline{1-1}  & [16; 39] & & & designated devices, it can & - \\ \cline{1-1}  & [16; 39] & authenticator applications & & be used without & - \\ \cline{1-1}  & & and act as a version of the & & internet access. & - \\ \cline{1-1}  & & authenticator application & & & businesses relying on \\ \cline{1-1}  & & which is used for & & & third-party applications. \\ \cline{1-1}  & & multifactor authentication. & & & - \\ \cline{1-1}  & & & & - & The capacity of malicious \\ \cline{1-1}  & & & & & software to steal and \\ \cline{1-1}  & & & & & impersonate the users. \\ \hline \hline \end{tabular}
\end{table}
Table 3: Various Types of MFA and its Pros and Cons.