A Novel Copyright Protection Scheme based on Visual Secret Sharing

IEEE-20180

A Novel Copyright Protection Scheme based on Visual Secret Sharing Surekhl1,Dr GN Swamy*2, Dr KRama Linga Redd/3

B

Associate Professor, Department of ECE, TRR College of Engineering, Patancheru, Hyderabad, Andhra Pradesh, INDIA

-

502 3i9

[email protected] *

Professor, Department of ECE, VR Siddhartha Engineering College, Kanuru, Vijayawada, Andhra Pradesh, iNDiA

-

520007

2gavini [email protected] I

Professor and HOD, Department of ETM, G.Narayanamma Institute of Technology

&

Science

Shai/pet, Hyderabad, INDIA -500008 [email protected]

Abstract-

In this paper the concept of Visual Secret Sharing

Visual Secret Sharing (VSS) is an interesting idea

and Discrete Wavelet Transform (DWT), are used to split the

proposed by Naor and Shamir [I] to share a secret binary

watermark into two random binary images called shares. One share is generated during watermark embedding phase and is kept secret with an arbitrator. The other share can be extracted from the controversial image whenever needed. Both the shares can be combined to decode the original watermark. The proposed scheme aims at re ducing the size of shares, improving the quality of extracted watermark, and decreasing the probability of false positives. Hence it offers

image among be recovered

n

participants such that the secret image can

without

any computations. A codebook

involving pixel expansion is used to split a secret image into

n

random looking images called shares. These shares

are printed onto transparencies and are distributed to the

n

participants. Simple stacking of all these transparencies at a later time can visually recover the secret.

better security when compared to the related schemes. The

Recently, many researchers used the concept of basic

simulation results reveal that the proposed scheme is robust

VSS with two participants to protect the copyrights of

to several image processing attacks.

digital images. The VSS based watermarking techniques defmed in [2]-[4] embeds the secret share in frequency

Keywords-

Copyright Protection, Digital Watermarking,

Discrete Wavelet Transform, Visual Secret Sharing.

domain version of the host image to result high quality watermarked images and to have good resilience to attacks. These techniques are sim ilar to traditional watermarking

I.

techniques in the way they satisfy the performance criteria.

INTRODUCTION

For example high robustness is achieved at the cost of

Due to rapid growth in computer and communication

sacrificing the payload and imperceptibility.

technologies, a variety of multimedia data is available on

To resolve this tradeoff, researchers in [5]-[ 12] have

the internet for open access. Many multimedia agencies are

proposed another category of VSS based watermarking

now depending on the internet for their commercial

schemes which doesn't alter the host image at all. Before

purposes. The ultimate availability of their data on the

publishing the host image these schemes first construct one

internet leads to data piracy. Therefore many people are

random image called an ownership share using the original

interested in protecting their intellectual data by adapting

watermark image, a secret key and some features extracted

copyright

protection

techniques.

Digital

image

from the host image. The ownership share is confidentially

watermarking is one such technique. In this process, before

time stamped and is kept secret with the arbitrator. During

an image is published, the copyright information of the

verification, a second random image called verification

owner

share is extracted from the controversial image using the

is

embedded

into

it

by

using

embedding algorithm

and

a secret

a

watermark

key. Whenever a

same secret key. The verification share is then overlaid on

controversy happens, the watermark can be extracted from

the ownership share to extract the watermark. Due to some

the controversial image using the same secret key and a

kind of pixel expansion used in creating shares the

watermark

extracted watermark have large size and low contrast.

extraction

algorithm.

The

watermark

embedding and extraction algorithms should be designed,

Since shares are needed to be saved by the arbitrator for

such that the hidden watermark can't be tampered after

copyright verification, the actual size of the shares should

attacks on the copyrighted image. The term robustness in

be as small as possible. This problem is more pronounced

watermarking

Other

when multiple watermarks are to be embedded into the

watermarking

same host image. In this case multiple shares (one for each

important

refers

criteria

to

to

this

be

attack

satisfied

resilience. by

algorithms are simplicity, imperceptibility, high capacity

owner) are to be generated and are to be registered with the

and security.

arbitrator. If the shares are large, it becomes heavy burden for the arbitrator to store all the shares. Hence, it is

ICCCNT'12 26 th_28th July 2012, Coimbatore, India

IEEE-20180

important to reduce the size of the shares as much as possible. In this paper, a novel watennark hiding scheme based on modified VSS and Discrete Wavelet Transfonn (DWT) is proposed. This scheme works in the same way as specified in the previous paragraph. When compared to the related

works,

the

proposed scheme has

(a)

three main

(b)

advantages. 1) The quality of extracted watennark is good. 2) The scheme results in no pixel expansion while creating the shares. 3) It reduces the probability of false positives. In addition to these advantages, the proposed scheme achieves

high robustness to several

image processing

attacks. The rest of the paper is organized as follows. In Section 2, we give the preliminaries needed in understanding the proposed watennarking scheme. Section3 describes the proposed

watermark

Experimental

results

hiding and

and

verification

comparisons

are

phases. given

II. VISUAL SECRET SHARING (VSS)

(c) Share2 (d) Decoded image The results of basic VSS with two participants are shown

in

Fig.1.

independent

Here

random

all

the

selection

pixels of

are

coded

by

Thus

no

columns.

infonnation is obtained by observing any group of pixe Is

A. Basic Visual Secret Sharing ( VSS) Scheme 2-o{-2

(d)

Fig. 1 Example of basic VSS scheme (a) Secret image (b) Sharel

in

Section4. Finally, Section 5 concludes the paper.

A

(e)

visual secret sharing is the basic model. It

splits a secret image into two random images called shares. The splitting is done in the following way. For each pixel in the secret image, a code consisting of four sub-pixels is substituted in each of the shares using a codebook given in Table 1. Each code has half white and half black sub pixels, independent of whether the corresponding pixel in the secret image is black or white. A white pixel is shared into two identical codes. A black pixel is shared into two complemental)' codes. While creating the shares, if the given pixel p in the original image is black, then the encoder randomly chooses one of the first two columns of Table.1. If the given pixel p is white, then the encoder randomly chooses one of the last two columns of Table. 1. The security of VSS lies in the random selection of these columns. To achieve high security the probability of selecting each column, for either pixel color should be same.

on each share. To decode the secret image, each of these shares has to be xeroxed onto transparent sheets. Stacking both these sheets will reveal the original secret. When the two shares are overlaid one above the other, as in Fig.I.d, the black pixels in the original image remain black and the white pixels turns gray. This contrast loss is due to the process of pixel expansion during share creation.

B. Modified Visual Secret Sharing ( VSS) Scheme In the basic VSS, each pixel in the original image is replaced with a code consisting of four sub-pixels in each share. This increases the size of each share to four times the original image and results in loss of contrast in the recovered proposed

image.

To

watermarking

overcome scheme

these

problems

exploits

a

codebook which is shown in Table 2. Here the codes are one pixel size and the decoding operation used is logical XOR. The results of using a modified codebook are shown in Fig. 2. Note that the decoded image in Fig. 2d is exactly

TABLE I

same in size and contrast as the original secret image.

CODEBOOK OF BASIC VSS SCHEME

TABLE 2

Pixel

White

CODEBOOK OF MODIFIED VSS SCHEME

Blac k

Pixel Prob.

Share I

Share2

Sharel Share2

+

the

modified

50%

50%

50%

50%

� � � � � � � � � � II II

Black

White

Prob.

50%

50%

50%

Sharel

•

D

•

D

Share2

•

D

D

•

EB

D

D

•

•

Sharel Share2


50%

IEEE-20180

Pixel in watermark

(a)

Black

White

1

Element in Y matrix

0

Ownership share

•

D

0

1

D

•

(b)

B. Watermark Extraction Phase The inputs to the watennark extraction algorithm are a gray level controversial image and the ownership share image. The corresponding output is a binary watennark image.

(c)

To extract a secret binary image Y from the features of

(d)

controversial image, the owner uses the same process and secret key which is used in the watennark hiding process.

Fig. 2 Example of modified VSS scheme (a) Secret image (b) Sharel

A verification share is constructed using the rules given in

(c) Share2 (d) Decoded image

Table4.

III. THE PROPOSED WATERMARKING SCHEME Un like

traditional

watennarking

schemes,

the

watennark is not embedded physically into the digital image.

Instead,

the

proposed

method

A

bitwise

Exclusive

OR

constructs

an

verification share and the extracted watennark is exactly

TABLE 4

VERIFICATION SHARE CONSTRUCTION RULES

A. Watermark Hiding Phase

Element in Y matrix

0

Verification share

•

The inputs to the watermark hiding algorithm are a gray and a binary watennark

then

same since there is no pixel expansion.

of the host image to hide a binary watermark.

H

is

the secret. Note that, the size of the ownership share,

ownership share and a verification share from the features

level host image

operation

perfonned on ownership and verification shares to reveal

B.

The

1

D

corresponding output is a binary image called ownership share. The size of the ownership share is same as the size IV. SIMULATION RESULTS

of watermark image. The host image

H is

first decomposed into} DWT levels

such that the size of each sub-band in the lowest DWT level is larger than the size of the watennark. A secret key

K

is used as a seed to generate a random list of

positions from the LL} sub-band, where watermark.

A

feature

image

P

F with

P

pixel

is the size of the

P

elements

is

constructed, by performing the average on a window of size 5x5 pixels centred at each selected pixel position Let

M be

Pi.

the population mean obtained by averaging all

the sample averages in the feature image.

For each

element in the feature image, if the sample average value is greater than or equal to the population mean

M,

then assign

logic I as the corresponding element in a binary matrix Y, otherwise assign logic

O.

To

verify

the

effectiveness

of

the

proposed

watennarking scheme a sequence of simulations were perfonned using MA TLAB Image Processing Toolbox. Fig.3 (a)-(c) shows three gray level test images (512x512) which are selected as host images. The binary watennark image to be hidden into the host image is of size 150x200 and is shown in Fig.3 (d). For the host image shown in Fig. 3(a) the resultant ownership share, verification share and the

extracted

watermark

for the proposed watermark

hiding scheme are shown in Fig.4.a-c. Note that the size of all these images is same as the original watermark. Also the extracted watennark quality is exactly same as the original watermark.

Finally an ownership share is constructed using the rules given in Table 3. This ownership share is time-stamped and is confidentially kept secret at arbitrator. During verification of copyright, the owner should provide the same secret key to the arbitrator, to retrieve another share called verification share. When this share is overlaid on the ownership share, the watermark can be revealed.

(a)

(b)

(c)

Fig. 3 Test images used in simulations

TABLE 3

OWNERSHIP SHARE CONSTRUCTION RULES


(d)

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The effectiveness comparison of the proposed scheme with some similar VSS-based watermarking schemes in the literature is given in Table 6. The comparison is mainly focused on the following properties: pixel expansion, extracted watermark quality and the probability of false

(a)

positives or indirectly security. Note that the scheme is

(c)

(b)

ideal if there is no pixel expansion, no contrast loss and if the probability of false positives is less. A false positive is

Fig. 4 Results of simulations (a) Ownership share (b) Verification share (c) Extracted watermark Peak Signal to Noise Ratio Correlation

a result of extraction of a watermark from an unauthorized image, which doesn't actually belong to the owner. Since, false positives encourage the malicious owners in claiming

(PNSR)

and Normalized

other unauthorized images, this problem should be avoided.

are used to evaluate performance of this

The proposed method of watermark hiding utilizes sample

watermarking scheme. PSNR is used to evaluate the

averages and central limit theorem to reduce false alarm

similarity of original and attacked gray level images. It is

probability.

(NC)

defined in terms of Mean Square Error

PSNR =10xlog

2 255

(MSE)

as follows:

From the results in Table 6, it is clear that only the proposed scheme satisfies all the criteria mentioned above.

--

MSE

V. CONCLUSIONS

(1) r

MSE =

and

H'iJ

c

1 -2: 2: (Hi,) _H\})2 rxc

(2)

Where

The concept of Visual Secret Sharing (VSS) is used to

HiJ

hide a digital watermark into Discrete Wavelet Transform of a host image. The features of the image are used to split

i�l }�l

the watermark into two random binary images called

denotes pixel color of original host image

denotes a pixel color of attacked watermarked

image, and

r x c

denotes the image size.

Normalized Correlation

(NC)

is used to measure the

similarity between the original and extracted watermark. It is defined as follows: w

=

One

share

during

watermark

other share is extracted from the controversial image combined to extract the original watermark. Unlike, the existing schemes, the proposed scheme don't expand the In the proposed watermarking method, the shares hide the

watermark without altering the host image. The simulation

_i_�l---,.l�_l

results reveal that the proposed scheme has satisfactory

______

robustness to several image processing attacks.

wxh

Bi,i

generated

during watermark extraction phase. Both the shares are

(3) Where

is

embedding phase and is kept secret with an arbitrator. The

shares. It also results in high quality extracted watermarks.

h

2:2: (Bi,) ffi B'i,)

NC

shares.

denotes pixel color of extracted w atermark

image from the original host when it is not altered and

B'iJ

denotes a pixel color of extracted watermark image when it is altered. To check attack resilience of the proposed scheme, some common image processing attacks were performed on the three host images. All the attacks were performed using MA TLAB software. The corresponding PSNR and NC values are listed in Table 5. The JPEG compression attack is performed by compressing the image with a quality factor 10. The blurring, sharpening and median filtering of the images were done with a window of size 3x3. A noise added image is obtained by adding 20% salt and pepper noise to the host image. The scaling of an image is done by first reducing the original host image size from 512x512 pixels to 256x256 pixels, and then zoomed to its original size by means of pixel replication. The cropped image is obtained by cropping 25% of the original host image. To test the robustness against rotation attack the original host image is rotated 10° in counter clock wise direction. From Table 5 it is clear that the proposed scheme results in most NC values closer to 1, indicating satisfactory

REFERENCES [1] M. Naor and A. Shamir, "Visual Cryptography," in Proceedings of Advances in Cryptology : Eurpocrypt '94, vol. 950, Springer,

Berlin, pp. 1-12, 1995. [2] C.S. Hsu and S.F. Tu, "Digital Watermarking Scheme with Visual Cryptography", in Proceedings of The International Multi Conference of Engineers and Computer Scientists, Hong Kong, China, 2008., pp. 659-66, [3] S-F Tu, and C-S Hsu, "Digital Watermarking Method Based on Image Size Invariant Visual Cryptographic Scheme", in IEEE Symposia and Workshops on Ubiquitous, Autonomic and Trusted Computing, 2009, pp.362-366. [4] Nagaraj V. Dharwadkar and B.B.Amberker, "Watermarking Scheme for Color Images using Wavelet Transform based Texture Properties and Secret Sharing", International Journal of Signal Processing, vol.6, no.2, pp. 93-100, 2010. [5] Hwang, R., "A Digital Image Copyright Protection Scheme based on Visual Cryptography," Tamkang Journal of science and Engineering, vol.3, no.2, pp. 97 - 106, 2002. [6] C-c. Chang and J-c. Chuang" "An image intellectual property protection scheme for gray-level images using visual secret sharing Strategy," Pattern Recognition Letters, vol. 23, no. 8. pp.931-941,2002. [7] M Hassan A, and M Khalili A, "Self Watermarking based on Visual Cryptography," in proc. of World Academy of SCience, Engineering and Technology, Oct 2005, vol. 8, pp. 159-162. [8] B Surekha , GN Swamy , K Srinivasa Rao , and A Ravi Kumar , "A Watermarking Technique based on Visual Cryptography," Int.

robustness for the given attacks.


IEEE-20180

Journal of Information Assurance and Security, voL 4, no,6, pp, 470-473, 2009, [9] D,C Lou, H,I(, Tso, and J,L Liu, "A copyright protection scheme for digital images using visual cryptography technique," Computer Standards and Interfaces, voL29, no,I, pp,125-131, 2007, [10] G'o'Park, EL Yoon, and KY Yoo, "A new copyright protection scheme with visual cryptography," inProc' of the Second Inl, Con! on Future

Generation Communication and Networking Symposia, 2008, pp, 60-63, [II] Y Xing, and JH He, "A new robust copyright protection scheme for digital images based on visual cryptography," in Proc,of the 2010 International Conference on Wavelet Analysis and Pattern Recognition,Qingdao, 11-14 July 2010, pp,6-1 \, [12] Chen TH, Chang CC, Wu CS, and Lou nc, 'On the security of a copyright protection scheme based on visual cryptography', Computer Standards & Inteifaces, voL 31, no,l, pp, 1-5, 2009,

TABLES

SIMULATION RESULTS OF PROPOSED WATERMARKING SCHEME Mandril

Boat

Lena

PSNR

NC

PSNR

NC

PSNR

NC

(dB)

(%)

(dB)

(%)

(dB)

(%)

Attacks JPEG (QF- I O%)

32.93

0.9842

30.42

0.9812

35.36

0.9752

Blurring (3x3)

30.52

0.9532

29.12

0.9427

32.64

0.9654

Sharpening (3x3)

29.61

0.9876

28.29

0.9749

32.54

0.9898

Histogram Equalization

26.97

0.8704

27.57

0.9842

4l.94

0.9630

Median Filter (3x3)

36.42

0.9943

31.69

0.9882

40.71

0.9972

Salt & Pepper Noise

34.05

0.9514

34.12

0.9383

34.20

0.9386

Scaling (1/2)

33.60

0.9843

30.99

0.9752

36.81

0.9876

Rotation (3° left)

29.59

0.8433

28.69

0.8483

30.68

0.8678

Cropping (10%)

36.11

0.8774

36.11

0.8546

36.21

0.9255

TABLE 6

COMPARISON OF VARIOUS SCHEMES

Domain

Pixel Expansion

Contrast loss

Frob, of false positives

Security

Hwang [5]

Spatial

2

Yes

Low

No

Chang and Chuang [6]

Spatial

9

Yes

High

High

Hassan and Khalili [7]

Spatial

2

Yes

Low

High

Surekha and Swamy[8]

Spatial

2

Yes

High

Low

Lou, Tso and Liu[9]

Frequency

2

Yes

Very high

No

Park, Yoon and Yoo[lO]

Frequency

No

No

Low

No

Xing and He[ll]

Frequency

2

Yes

High

Yes

Proposed Scheme

Frequency

No

No

Very low

High

� Schem e
