Transcript 下載/瀏覽
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
received : April 19, 2006
revised : July 16, 2006
1
Xinpeng Zhang
2001, Communication and Information Engineering, Shanghai
University ,Master's Degree
2004, Communication and Information Engineering, Shanghai
University ,Ph.D. degree
2
Shuozhong Wang
1966, Graduated from Department of Radio and Electronics,
Peking University
1982, Received Ph.D. from University of Birmingham, UK
1983-1985, Research Fellow, Institute of Acoustics, Chinese
Academy of Sciences
1993-1994, Visiting Associate Scientist, EECS, University of
Michigan, USA
1985-present, Associate Professor, Professor, School of
Communication and Information Engineering, Shanghai
University
3
Outline
1.
2.
3.
4.
5.
6.
7.
8.
Introduction
Sensitivity attack
Watermark detector
Embedding algorithm
Detection algorithm
Security analysis
Experimental results
Conclusions
4
Introduction
1.
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
5
Sensitivity attack(1/3)
1.
Attacker possesses a watermarked image and an
available detector
Sensitivity
attack
Original image
Watermarked image
Watermark
embedding
Watermark
2.
watermark
detector
Not watermarked
Remove or change the embedded without causing
serious distortion
6
Sensitivity attack(2/3)
Decision boundary :
between the “Watermarked” and
“Not watermarked” regions is a
hyper-plane in a multidimensional
space.
Not watermarked
Watermarked
Decision boundary
7
Sensitivity attack(3/3)
N
A (n n / n) : perpendicular to the decision boundary
n 1
1/ n : shows how sensitive the detector is to modification
in the direction of each vector
n : is either +1 or -1 indicates addition or subtraction
Subtracts A from the watermarked copy with an increasing
strength A until the detector reports that no watermark is present.
Thus, the embedded watermark is removed.
8
Watermark detector
Public watermark detector
Detection
function F
Output 1
(Watermarked)
> Threshold
≤ Threshold
Test image
Black box
Output 0
(Not watermarked)
Watermark detector : provide adequate information about an
embedded watermark
9
Embedding algorithm(1/6)
C2,3 C2,0
DWT
3-levels
C2,2 C2,1
C1,2
C1,0
C0,0
C1,1
C0,2
C0,1
IDWT
Watermarked image
Watermark
10
Embedding algorithm(2/6)
Cl,θ p,q
N l,θ
C l,θ
63
-34
49
10
7
13
-12
7
63
-34
-31
23
14
-13
3
4
6
-1
-31
23
15
14
3
-12
5
-7
3
9
-9
-7
-14
8
4
-2
3
2
-5
9
-1
47
4
6
-2
2
3
0
-3
2
3
-2
0
4
2
-3
6
-4
3
6
3
6
5
11
5
6
0
3
-4
4
3.25
15
2.75
-3.75
5.17
1
1
1
1
4
16
4
2.25
4
16
16
11
Embedding algorithm(3/6)
Wl,θ ={
0.16
0.16
0.16
0.22
6
1.00, if l =0
0.32, if l =1
0.16, if l=2
0.32
0.32
, if θ =1
} { 12, otherwise
}
1
0.452
1
1.414
12
Embedding algorithm(4/6)
1. Generate( M 1 )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 :
m
p,q ,
Sl,θ
0mM
mutually independent and satisfy a standard Gaussian
distribution with zero mean and unit standard deviation
13
Embedding algorithm(5/6)
um C m
C p,q Cl,θ p,q -
Tl,θ p,q : modified DWT coefficients
m 0 Am
M
'
l,θ
where Tl,θ
m
m
p,q
Sl,θ
p,q
Wl,θ
N l,θ
2
l
θ Wl,θ
Am Tl,θm p,q
θ
l
p
θ
2
q
um C
l
p
C
l,θ
p,q -C l,θ
T p,q
m
l,θ
q
All modified DWT coefficients are inversely transformed to yield
a watermarked copy
14
Embedding algorithm(6/6)
1.
2.
According to the central limit theorem
Am is very close to its mean 1
All um C are approximately 0
Standard deviation of um C
σ u C
C
l,θ p,q -C l,θ Wl,θ
l
θ
p
2
q
N
l
l,θ
Wl,θ2
θ
2552 N 1N 2
PSNRw 10 log 10 2
(
M
1
)
u
15
Detection algorithm (1/2)
F U
E
2
U M u0 C
- u C
M
"
"
m 1
m
E 0.8 M- M σu C"
1. If F 0
F 0
output “ Watermarked ”
output “ Not watermarked ”
16
Detection algorithm (2/2)
1.
If test image contains watermark, all u m close to 0
U 0
E
0
2
F
2.
If test image contains no watermark
U
M -M σ u C"
-
t
2π
-
t2
2
e dt 0.8
M -M σ u C" -E
E
0
2
To ensure error < 10-9, M 189 avoid excessive distortion
F -
3.
17
Security analysis
1.
Attacker does not know u m
and is impossible to estimate T m by measuring the
sensitivities of u m
2.
The detection function of the attacked signal always
greater than 0 ( F > 0).
This means the sensitivity attack cannot remove the
embedded watermark.
18
Experimental results
Image
Detection function
F
Original
-1.7104
Watermarked
1.5104
A 9601280 still image captured
by a digital camera was
used as the original test signal.
The system parameter M=189
19
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.
20