Cryptography Reference
In-Depth Information
Notations:
S: The target secret image with size mm.
t: More than or equal to t shadows possessed by the participants that can
recover the target secret image.
n: The number of participants.
S
i
: Each pixel of the target secret image S;i = 1; 2; ;m
2
.
B
i;j
: The gth block (size of 18) in the jth cover image, where j = 1; 2; ;n
and g = 1; 2; ;
l
m
2
t
m
. Each block is made of 8 pixels.
B
(d)
g;j
: The dth pixel of block B
i;j
. The bit string of each pixel B
(d)
g;j
is shown
as the form (x
d1
;x
d2
; ;x
d7
;x
d8
) where 1 d 8.
B
g;j
: The gth block in the jth stego-image.
f
j
: The feature value of the jth stego-image (or the jth cover image) when the
block B
(d)
g;j
(orB
g;j
) is processed, where the stego-image size is of 2m 2m.
f
j
= (x
11
;x
12
;x
13
;x
14
;x
21
;x
22
;x
23
;x
24
) is created from the first two pixels
in block B
(d)
g;j
(orB
g;j
), for j = 1; 2; ;n. If f
j
is equal to one of feature
values f
1
;f
2
; ;f
j1
, keep looking at the next possible pair of pixels in
block B
(d)
g;j
(orB
g;j
) following a xed order. (Note that there are C(8; 2) 2
= 56 possible choices in a block.)
l
m
2
t
m
PV y
(g
j
: The gth pixel in jth shadows, g =
1; 2; ;
and j =
1; 2; ;n. The bit-string format of PV y
(g
j
is (y
g1
;y
g2
; ;y
g8
).
p: 256 for the Galois Field GF(2
8
).
Revised Algorithm of High-Capacity and Applications (RAHA)
Part I: Aim at the high capacity approaching:
For g = 1; 2; ;
l
m
2
t
m
, do a loop as follows:
Step 1. Generate the polynomial q
g
(x) of t 1 degrees as follows:
q(x) = (a
0
+ a
1
x + a
2
x
2
+ ::: + a
i1
x
i1
)
where a
0
= S
i
;a
1
= S
i
+ 1; ;a
t1
=S
i+t1
;i = (g1)t, and all operations
are over the Galois Field GF(2
8
).
Step 2. Get block B
g;j
from the jth cover image. Set f
j
as the feature value
of block B
g;j
;j = 1; 2; ;n.
Step 3. Compute PV y
(g
j
= q
g
(f
i
);j = 1; 2;:::;n:
Step 4. Assign each PV y
(g
j
to the jth shadow, j = 1; 2; ;n.
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