# A Systematic Survey of Multi-Factor Authentication for Cloud Infrastructure
## 4 Analysis of Authentication Factors
### Comparison of Factors for Authentication
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Approach** & **Advantages** & **Limitations** & **Ref.** \\ \hline Face Recognition & Convenient, quick, and efficient & Large storage requirement, can create data vulnerability, compromised biometric is irrecoverable & [23; 67; 68] \\ \hline Fingerprint Scanner & Ease of use, cost-effective & Scanners may fail, easy to replicate fingerprint, compromised biometric is irrecoverable & [69; 70; 71] \\ \hline Geographical Location & Effective in case the user needs to be present at a particular location & GPS may not be accurate at some locations & [61; 72] \\ \hline Ocular-based Methods & Very efficient and difficult to spoof & Need high-quality camera and robust mathematical techniques, compromised biometric is irrecoverable and cannot be changed & [23; 73; 74] \\ \hline OTPs & Extra layer of security, hard to crack, expires after defined time & User availability required, lack of power backup, network issue, vulnerable to man-in-the-middle attacks & [20; 75; 76] \\ \hline SmartPhone & Code regenerated in defined time & User availability required, lack of power backup, network issue, invalid codes for clock & [21; 77; 27] \\ Applications & gap, hence safe from attacks & de-synchronization between device and service & \\ \hline SmartCards & More secure using encryption technology & Card may get lost, the chip may be damaged, radio interface for two-way communication & [78; 79; 80] \\ \hline Thermal Image Recognition & Efficient, can be used from a large distance & Different thermal image in case of fever & [23; 81; 82] \\ \hline Vein Recognition & Efficient, accurate & Expensive, but still vulnerable to spoofing attacks at the current stage, compromised biometric is irrecoverable & [61; 71; 83] \\ \hline Voice Recognition & Convenient, quick and efficient & False negative in the loud background, change in voice due to sickness; compromised biometric is irrecoverable & [61; 84; 85] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Advantages and Limitations of Authentication Approaches. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline
**Authentication Approach** & \begin{tabular}{l} **Brute-Force** \\ **Attack** \\ \end{tabular} & \begin{tabular}{l} **Guess** \\ **Attack** \\ \end{tabular} & \begin{tabular}{l} **Phishing** \\ **Attack** \\ \end{tabular} & \begin{tabular}{l} **Spoofing** \\ **Attack** \\ \end{tabular} & \
\begin{tabular}{l} **Impersonation** \\ **Attack** \\ \end{tabular} &
\begin{tabular}{l} **Ref.** \\ \end{tabular} \\ \hline Face Recognition & No & No & No & Yes & No & [23; 67; 68] \\ Fingerprint Scanner & No & No & No & Yes & No & [61; 72] \\ Geographical Location & No & No & No & No (retina) \& Yes ((\) iris) & No & [23; 73; 74] \\ Ocular-based Methods & No & No & Yes & No & Yes & [20; 75; 76] \\ OTPs & No & No & Yes & No & Yes & [14; 70; 71] \\ Password/PIN & Yes & Yes & Yes & No & Yes & [14; 70; 71] \\ SmartPhone Applications & No & No & Yes & No & Yes & [21; 77; 78] \\ SmartCards & No & No & No & Yes & Yes & [78; 79; 80] \\ Thermal Image Recognition & No & No & No & No & No & [23; 81; 82] \\ Vein Recognition & No & No & No & Yes & No & [61; 71; 83] \\ Voice Recognition & No & No & No & Yes & No & [61; 84; 85] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Different authentication approaches and their vulnerability to various attacks.