Table 5.

Security comparison.

Attack and Security Property	Yeh et al.'s Protocol	Shi et al.'s Protocol	Our Protocol
Stolen-verifier attack	Secure	Secure	Secure
Insider attack	Secure	Secure	Secure
Replay attack	Secure	Secure	Secure
Man-in-the-middle attack	Secure	Secure	Secure
Gateway impersonation attack	Secure	Secure	Secure
User impersonation attack	Secure	Secure	Secure
Sensor impersonation attack	Insecure	Secure	Secure
Mutual authentication	No	Yes	Yes
Perfect forward secrecy	No	Yes	Yes
Key agreement between user and sensor	No	Yes	Yes
Session key attack	Insecure	Insecure	Secure
Stolen smart card attack	Insecure	Insecure	Secure
Sensor energy exhausting attack	Insecure	Insecure	Secure