Cryptography Reference
In-Depth Information
FIGURE 16.5
The block of a stego-image in Chang et al.'s scheme.
Decide six moduli that are pairwise relatively prime M
ij;1
, M
ij;2
,
M
ij;3
,..., and M
ij;6
, where each modulusM
ij;a
, for 1 a 6 , is the
prime number greater than R
ij;a
.
Step 2:
Calculate the Y
ij
integer by Equation 16.4. Suppose that the binary
representation of the Y
ij
is (y
1
y
2
:::y
e
). Note that the number of
binary bits of Y
ij
has to be a multiple of 4.
Step 3:
r
X
R
i
M
Y = (
M
i
I
i
)
(16.4)
i=1
Step 4:
Four interim authentication bits a
1
;a
2
;a
3
; and a
4
are computed by
Equation 16.5.
a
1
a
2
a
3
a
4
= (y
1
y
2
y
3
y
4
)(y
5
y
6
y
7
y
8
):::(y
e3
y
e2
y
e1
y
e
): (16.5)
Step 5:
Denote b
1
;b
2
;b
3
; and b
4
as the current four watermark bits; four
check bits p
1
, p
2
, p
3
, and p
4
can be computed by Equation 16.6.
p
1
p
2
p
3
p
4
= (a
1
a
2
a
3
a
4
) (b
1
b
2
b
3
b
4
):
(16.6)
Step 6:
Replace the four LSBs x
0
v
0
w
0
z
0
with the computed check bits p
1
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