Table 3.

Efficiency comparison.

Protocol	Computational Cost
	User	Sensor	Gateway
Yeh et al.'s protocol	2M +1R+1A+4H	2M +1R +1A+ 1P +1H	3M +1R+1P + 1H
Shi et al.'s protocol	3M +5H	2M +3H	1M +4H
Our protocol	3M +7H	2M +4H	1M +4H