Cryptography Reference
In-Depth Information
FIGURE 15.1
The format of B
i
j , where x
i
, w
i
, v
i
, and u
i
are represented as binary pattern.
Notations:
q(x): The (t 1)-degree polynomial of q(x) = (a
0
+ a
1
x + a
2
x
2
+ ::: +
a
t1
x
t1
)mod p, where p = 251.
S: The target secret image with the size of mm. The pixel S
i
2 [0; 250] in
S, 1 i m
2
. It is caught by up-to-down and left-to-right in order.
I
j
: The jth cover image with the size of 2m2m pixels. There are m
2
blocks,
B
0
ij
s, where each one is the size of 2 2 containing four pixels as x
i
, w
i
,
v
i
, and u
i
in the order of left-to-right and up-to-down and 1 i m
2
and
1 j n. The pixel format of B
ij
is shown in Figure 15.1.
0
I
j
: The jth stego-image with the size of 2m2m. There are m
2
blocks,
B
ij
s.
B
ij
is stego-block when the secret is embedded the B
ij
. The corresponding
pixels in
B
ij
to B
ij
is xˆi,
i
; w
i
; v
i
, and u
i
, respectively.
b
i
: Generate a random bit-string with the form of (b
1
;b
2
; ;b
m
2
), where
1 i m
2
.
The procedure to generate the stego-image, named as Proc-Lin-Tsai, is
briefly given in the following:
Procedure Proc-Lin-Tsai
Input: S, I
j
, j = 1; 2; ;n.
Output:
I, j = 1; 2; ;n.
Step 1. Generate the random bit string (b
1
;b
2
; ;b
m
2
).
Step 2. Set a
0
=S
i
, i 2 [1;m
2
]. For each S
i
chooses a (t1)-degree polynomial
q(x)=(a
0
+ a
1
x + a
2
x
2
++ a
i1
x
i1
) mod p, where randomly choose t-1
value a
1
;a
2
; ;a
i1
under the modulo p. Calculate yi
i
= q
i
(x
i
), where x
i
is obtained and defined from xi
i
in the I
j
and represent y
i
as the bit string
with the form of yi
i
= (y
i1
;y
i2
; ;y
i8
).
B
ij
, comprised of the four bit strings as
Step 3. Generate the stego-block,
x
i
= (x
i1
;x
i2
; ;x
i8
),
w
i
= (w
i1
;w
i2
; ;w
i5
, b0
i
, y
i1
;y
i2
),
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