. 2015 Nov 30;15(12):29841–29854. doi: 10.3390/s151229767

Table 1.

Notation.

ID_i, pw_i	Identity and password pair of user U_i
SID_j	Identity of sensor node S_j
ID_s	Identity of smart card
K	Secret key only know to GWN
x_s	Secret value of GWN and S_j
K_S	Session key
RN_i, RN_j, RN_G	Random numbers selected by U_i, S_j and GWN, respectively
T_i, T_i′, T_j, T_G, T_G′	The timestamp values
h(·)	A collision free one-way hash function
f(x, k)	Pseudo-random function of variable x with key k
A →B:M	A sends message M to B through a common channel.
A ⇒ B:M	A sends message M to B through a secure channel
⊕	The exclusive-or (XOR) operation.
M₁\|\|M₂	Message M₁ concatenates to message M₂.