. 2017 Mar 21;17(3):644. doi: 10.3390/s17030644

Table 1.

Notations.

Value	Description
$U_{i}$	Remote user
$S_{j}$	Sensor node
$G W N$	Gateway node
$I D_{i}$ , $P W_{i}$	Identity and password of $U_{i}$
$B i o_{i}$	Biometric information of $U_{i}$
$P W_{i}^{n e w}$	New password of $U_{i}$
u	Random number of $U_{i}$
$I D_{s}$	Identity of smart card
$T I D_{i}$	Temporary identity for $U_{i}$ ’s next login
$S I D_{j}$	Identity of $S_{j}$
K	Secret key generated by the $G W N$
$R N_{r}, R N_{G}, R$	Random numbers
$h (\cdot)$	One-way hash function
$H (\cdot)$	Biohash function
$f (x, k)$	Pseudo-random function of variable s with key k
$X \| \| Y$	Concatenate operation
⊕	XOR operation
$T_{1}$ , $T_{2}$ , $T_{3}$ , $T_{4}$	Current time stamp values
$K_{S}$	Session key
$Δ T$	The maximum of the transmission delay time