Table 2: Security comparison of the related scheme and the enhanced scheme.

Security featuresLi-Hwang’s scheme [12]Das’s scheme [13]Enhanced scheme

User impersonation attackPossiblePossibleImpossible
Sever masquerading attackPossiblePossibleImpossible
Password guessing attackPossiblePossibleImpossible
Insider attackPossiblePossibleImpossible
Mutual authenticationNot providedNot providedProvided