Information Technology Reference
In-Depth Information
01
01
-
Extract all LSBs from
Y
r
,
C
r
=
is obtained.
1111111
0
1000000
0
0110110
0
0000101
0
-
Set all LSBs of
Y
r
to 0, and obtain
Y
r
=
.
11
10
-
Hash
Y
r
.
-
Perform pixel by pixel ex-or operation between
H
r
and
C
r
to obtain water
mark image block
A
r
=
by CAA and obtain
H
r
=
10
11
.
Analysis and Comparative Study
The inherent advantages ofthe proposed scheme can be summarised as follows:
(a) The greatest advantage ofour scheme is the flexibility ofadjusting key size
without any overhead. This is possible due to modular structure ofCellular Au-
tomata.
(b) The Table 4 shows the result where in each ofthe image, watermark has
been inserted according to proposed scheme (column 4 to 7) gives better PSNR
values than MD5 (column 8). Moreover as extension field parameter
p
increases
in
CAA
, PSNR value improves (Table 4). The robustness ofCAA based one-
way hash function, as noted in Section 3.3, has resulted in the superior quality
watermarked image.
Table 4.
Comparison of PSNR values using CAA for different p and MD5
Image Data Block PSNR Values in dB unit
name in size Wong-Memon method
Bytes p=1 p=2 p=4 p=8 MD5
Sachin 522835 14x3051.126629 51.201994 51.29048 51.541979 51.013072
SkylineArch 964451 72x6052.013388 52.216852 52.427391 52.811862 51.034981
Lena 1064071 60x9053.23367 53.295081 53.463457 53.788033 51.243123
Concord 1485604 80x8453.830272 53.884655 54.020056 54.526984 51.317890
Rabbit 964451 80x7252.177280 52.307440 52.443773 52.725227 51.103782
(c) The most effective attack on image authentication is Holliman-Menon at-
tack or Vector Quantization attack [6]. CAA based watermarking is tuned to
counterfeit this attack as a built-in function whereas all other hash functions
(including MD5) defend the attack externally which effectively decreases the
insertion/extraction speed ofwatermarking.
4 Conclusion
This paper reports GF(2
p
) Cellular Automata (CA) based Authentication
(CAA) scheme. The scheme has been employed to insert fragile watermark in
images. Security ofCAA against known attacks and its execution speed are
emphatically better than those ofMD5. Future prospective ofthe
CAA
lies in
