Cryptography Reference
In-Depth Information
15.4.3 Main Algorithms
In this subsection, Wang et al.'s main algorithm, Secret Embedding and De-
tecting Algorithm (SEDA for short) and Target Secret Image Recovery Al-
gorithm (TSIRA) are presented. More notations are given together with the
above-mentioned notations as follows.
Notations:
I
j
: The jth cover image with the size 2m 2m pixels.
I
j
The jth stego-image with the size of 2m 2m.
B
(d)
g;j
The dth pixel value of the gth block B
g;j
in the jth cover image.
B
(d)
b;j
The dth pixel value of the gth block B
g;j
in the jth stego-image.
K: A secret key K used in the hash function.
Secret Embedding and Detecting Algorithm: The SEDA aims at
the secret embedding and detecting authentication.
Input: S;I
j
;j = 1; 2; ;n;k.
I
j
;j = 1; 2; ;n.
Output:
Step 1. Get the distinct feature-value f
j
= (x
11
;x
12
;x
13
;x
14
;x
21
;x
22
;x
23
;x
24
)
from B
g;j
of the cover image If
j
, where j = 1; 2; ;n. If f
i
is equal to one
of the feature-values f
1
;f
2
; ;f
j1
, then keep looking for the next pair of
pixels in block B
g;j
.
Step 2. Call RAHA to compute PV y
(g)
j
= q
g
(f
i
) and let each PV y
(g)
j
be
the bit-string format as (y
g1
;y
g2
; ;y
g8
).
Step 3. Apply IPLA to generate a pattern-string. Inspecting each block
B
g;j
, set the bit string of (y
r1
;y
r2
; ;y
r8
) to be the input of IPLA,
for g = 1; 2; ;
l
m
2
t
m
. The output of IPLA, a k-bit pattern-string of
(p
1
;p
2
; ;p
m
2
t
) is then generated after
l
m
2
m
blocks B
0
g;j
s are given.
t
Step 4. According to CRC-based detecting authentication procedure, gener-
ate
l
m
2
t
m
l
m
2
t
m
authentication codes of (c
g1
;c
g2
); ;c
0
g8
s , for g = 1; 2; ;
.
Step 5. Arrange all pixels in block B
g;j
, for g = 1; 2; ;
l
m
2
t
m
, as the fol-
lowing rule:
B
g;j
= (x
11
; ;x
16
;y
g1
;c
g1
),
B
g;j
= (x
21
; ;x
26
;y
g2
;c
g2
),
B
g;j
= (x
31
; ;x
36
;y
g3
;c
g3
),
B
g;j
= (x
41
; ;x
46
;y
g4
;c
g4
),
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