Table 2.

Security comparison of the related scheme and the enhanced scheme.

Security features	Li-Hwang's scheme [12]	Das's scheme [13]	Enhanced scheme
User impersonation attack	Possible	Possible	Impossible
Sever masquerading attack	Possible	Possible	Impossible
Password guessing attack	Possible	Possible	Impossible
Insider attack	Possible	Possible	Impossible
Mutual authentication	Not provided	Not provided	Provided