مقاومة الحق Resisting the Truth مقاومة الحق Resisting the Truth.
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Transcript of 1 Watermarking Scheme Capable of Resisting Sensitivity Attack IEEE signal processing letters, vol....
1
Watermarking Scheme Capable
of Resisting Sensitivity Attack
IEEE signal processing letters, vol. 14, no. 2, February. 2007, pp. 125-128 Xinpeng Zhang and Shuozhong Wang
2
Outline1. Introduction2. Sensitivity attack3. Watermark detector4. Embedding algorithm5. Detection algorithm6. Security analysis7. Experimental results8. Conclusions
3
Introduction1. This letter proposes a watermarking scheme
capable of defeating the sensitivity attack
a novel tailor-made embedding algorithm a corresponding detection mechanism
are designed to “mislead” the attackers: get a “fake” signal
4
Sensitivity attack(1/3)1. Attacker possesses a watermarked image and an
available detector
2. Remove or change the embedded without causing serious distortion
Original imageWatermark
embedding
Watermarked imagewatermarkdetector
Sensitivityattack
Not watermarkedWatermark
5
Sensitivity attack(2/3)
Not watermarked Watermarked
Decision boundary
Decision boundary : between the “Watermarked” and “Not watermarked” regions is a hyper-plane in a multidimensional space.
6
Sensitivity attack(3/3)
N
n
nnnA
1
)/(
n/1
n
: perpendicular to the decision boundary
: shows how sensitive the detector is to modification in the direction of each vector
: is either +1 or -1 indicates addition or subtraction
Subtracts from the watermarked copy with an increasing strength until the detector reports that no watermark is present. Thus, the embedded watermark is removed.
AA
7
Watermark detector
Public watermark detector
Detectionfunction F
> Threshold
≤ Threshold
Output 1 (Watermarked)
Output 0 (Not watermarked)Black box
Test image
Watermark detector : provide adequate information about an embedded watermark
8
Embedding algorithm(1/6)
C2,
3
C2,
0C1,0
C0,0C2,
2
C2,
1
C1,2 C1,1
C0,2 C0,1
DWT3-levels
Watermark
IDWT
Watermarked image
9
Embedding algorithm(2/6)
p,qCl,θ
63 49-34 7
-131423-31
10
15
-1
7
6
-12
4
13
3
93-75-12314
2
-303
6447-19-5
23-248-14-7-9
6511
-3
5
-2
2
2
6
40-23
3-46
0 -4
3
3 4
6
l,θC l,θN
1 1
1 14
4 4
16
16
16
63 -34
-31 2315
3.25 -3.75
5.17
2.75
2.25
10
Embedding algorithm(3/6)
0.16 0.16
0.160.226
0.32
0.32 0.452
1
1
1.414
l,θW ={ } { }θl
21.00, if =00.32, if =1l
l0.16, if =2 1 , otherwise, if =1
11
Embedding algorithm(4/6)
1M
Mm, p,qS ml,θ 0
mutually independent and satisfy a standard Gaussian distribution with zero mean and unit standard deviation
1. Generate( )data-groups in a pseudo-random manner
2. The number of elements in each data group is equal to that of the host DWT coefficients, and all elements in the groups :
12
Embedding algorithm(5/6)
l θ l,θ
l,θ
l,θ
ml,θm
l,θ W
N
W
p,qSp,qT 2
l θ p q
ml,θm p,qTA 2
l θ p q
ml,θl,θl,θm p,qTC-p,qCu C
M
m
ml,θ
m
ml,θ
'l,θ p,qT
A
u-p,qCp,qC
0
C
where
All modified DWT coefficients are inversely transformed to yield a watermarked copy
: modified DWT coefficients
13
Embedding algorithm(6/6)
1. According to the central limit theorem is very close to its mean 1 All are approximately 0
2. Standard deviation of
Cum
mA
l θl,θl,θ
l θ p ql,θl,θl,θ
u WN
WC-p,qC
Cσ2
2
Cum
)1(
255log10
2
212
10 M
NNPSNR
uw
14
Detection algorithm (1/2)
M
m
"m
" Cu-CuMU1
0
"u CσMM-.E 80
2
EUF
1. If output “ Watermarked ” output “ Not watermarked ”
0F
0F
15
Detection algorithm (2/2)
1. If test image contains watermark, all close to 0
2. If test image contains no watermark
3. M 189 avoid excessive distortion
0 U
02
E
F
-ECσ-MM.dt eπ
tCσ-MM U "
u
t-
-
"u
802
2
2
02
E
-F
mu
16
Security analysis
mu mT
1. Attacker does not knowand is impossible to estimate by
measuring the sensitivities ofmu
2. The detection function of the attacked signal always greater than 0 ( F > 0).
This means the sensitivity attack cannot remove the embedded watermark.
17
Experimental resultsImage Detection
function F
Original -1.7104
Watermarked
1.5104
A 960 1280 still image captured by a digital camera wasused as the original test signal. The system parameter M=189
18
Conclusions
1. The proposed watermarking scheme is capable of defeating the sensitivity attack.
2. The corresponding detection mechanism can mislead the attackers.
3. The output of detector cannot be used to remove watermark with low distortion.