A Lightweight Buyer-Seller Watermarking Protocol

Table 1

Performance comparison.

	MW [11]	LYTC [15]	Present
MSE $\sigma$	$2{\alpha }^2$	$2{\alpha }^2$	${\alpha }^2$
Seller time $t_S$	$n(T_e+T_m)$	$n(T_e+T_m)$	$T_d$
Buyer time $t_B$	$n{T}_d$	$n{T}_d+T_{sk}$	$T_d$
WCA time $t_W$	$n{T}_e$	$n{T}_e$	$2T_e$
Seller overhead $C_S$	$n{l}_N$	$n{l}_X+n{l}_N$	$n{l}_X+l_N$
WCA overhead $C_W$	$n{l}_N$	$n{l}_N$	$2n{l}_W+2l_N$

$T_e$: the computation time for an asymmetric encryption.
$T_d$: the computation time for an asymmetric decryption.
$T_m$: the computation time for a modular multiplication
$T_{sk}$: the computation time for generating a pair of public/private key.
$T_{sk}\gg T_d$.
$n$: the number of DCT coefficients to be manipulated.
$l_X$: the size of one image element $x_i$.
$l_N$: the size of a RSA modulus $N$.
$l_W$: the size of one watermark element $w_i$.