Scheme	From user to server		From server to user		Total cost
Scheme	Message	Cost	Message	Cost	Total cost
Proposed scheme	h(ID_i), F_i	256 bits		256 bits	512 bits
Khan et al. (2011)	CID_i, T_i, d, C_i	384 bits	C2,Ts	192 bits	576 bits
Wang et al. (2009)	ID_i, CID_i, N_i,T	448 bits	a’, T^*	192 bits	640 bits
Das et al. (2004)	CID_i, N_i, C_i, T	448 bits	-	-	448b its