Table 3.

Comparison of authentication techniques.

Authors	Features	Auth Tiers	Control Agent	Pros	Cons
Banyal RK et al. [93]	Arithmetic-based CAPTCHA calculation, OTP, and IMEI-based authentication mechanism	3	Server	Resistance to multiple attack type	Computational complexity
Emam AHM [94]	Authentication through dynamic link sent on registered email address	2	Server	Cost-effective	Email address may get compromised
Kumar S et al. [95]	OTP entered through personal device	2	Client and Server	OTP needs to be entered using personal device	Access lost if registered Device is lost or damaged
Usman AA et al. [96]	Security token generated using preshared pin numbers, location, and time	2	Client and Server	Cost-effective	Clock synchronization problem
Liu S et al. [97]	Sends QR code to register mobile device’s Bluetooth address	2	Server	Cost-effective	Mutual authentication not considered
Ahmad S et al. [98]	Smart card and biometric scanning	3	Server	Multiple factors required to access services	Smart card mandatory
Singh TG et al. [56]	Based on graphical patterns	2	Server	User convenience	Patterns are predictable
Soni P et al. [99]	Splitting and distribution of OTP over different channels	3	Server	Difficult to listen covertly	User onconvenience
Dhamija A [100]	Requires hardware token	2	Server	Resistant to different types of attacks	Expensive solution