) , k= 1, 2, 3,4....N (1)International Journal of Scientific & Engineering Research, Volume 4, Issue 8, August-2013 930
ISSN 2229-5518
Security of Medical Images by Discrete Sine
Transform Encryption Algorithm
Shaifi Goyal, Reecha Sharma
Index Terms— DST, Medical image, watermarking, chaotic table.
—————————— ——————————
Medical image watermarking algorithm is suitable method used for enhancing security, authentication, reliability and confidentiality of medical data, which is crucial and used for further diagnosis and reference. Image encryption algorithm protects the data from an unauthorized access. Encryption is a tool of security that aims to provide protection in the ciphers of any kind of messages. The applications of digital multime- dia have grown tremendously in the last five years, security and legal issues became more and more important. Water- marking, which is the embedding of a signal (known as the watermark) into the original multimedia element is one meth- od that has been proposed for the protection of digital media elements such as audio, video, and images. [2]
Chaotic systems are nonlinear dynamic behaviour;
they are sensitivity to the initialize conditions and generate highly complicated signals. Because chaotic systems have good properties, chaotic systems are widely used in commu- nications, optimization, control and image processing et al. In
1989, Matthews used discrete chaotic dynamical systems in cryptography firstly [1]. He derived a one-dimension chaotic
map, which is used to generate a sequence of pseudo-random numbers. Image encryption has its own specifications such as en-cryption speed, compatibility to image format and com- pression standards, and real-time implementation etc., there- fore requires a special design of the encryption algorithm.
In this paper, I propose an encryption algorithm based on im- age watermarking with encryption by DST domain. By setting the key to prevent recover and repair the watermark in the unauthorized situation. This transform helps in the selection of regions on basis of their sine energies. Data is hidden be- hind the region of not interest (RONI).
The simulation results show that the encrypted images are
robustness for noise disturbing and geometrical attack. We
have also improved the normalised cross- correlation of an
image based on chaotic system.
The proposed study aims to explore the possibility of using
chaotic or chaos-based encryption techniques by DST to pro- tect medical images and provides high level of security in effi- cient and reliable way.
The rest of the paper is organized as follows. Section 2
gives detailed analysis of the proposed algorithm. The effect of noise on the decryption process is discussed in Section5. The last section gives the concluding remarks.
Loaded the image of CT brain in the matlab. Here we use brain image as a binary medical image and is of size 128×128.
Logical data is a binary data which have been hide using orig- inal image. Here ‘copy right’ image is a logical image of size
32×32.
In the sine transform values in the chaotic table can be regard-
ed as a feature vector of the medical image.DST coefficients
reflects the visual characteristics of medical image.
DST presents a new approach for image encryption based on
the chaotic table. Discrete sine transform is energy based theo-
ry. It is well known for analysis of signal or images in ROI and RONI. Region of interest contains useful information and must be secured from attacks or noises.
For medical images DST is defined as:
N
y(k)=∑ x(n) sin(π ) , k= 1, 2, 3,4....N (1)
n=1
Here n is pixel number, k is number of pixels in a size of im- age, N is natural number.
For both joint photographic group(JPEG) and moving ex- pert group(MPEG) we use DST.A watermarking algorithm that uses DST is more compatible.
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International Journal of Scientific & Engineering Research, Volume 4, Issue 8, August-2013 931
ISSN 2229-5518
Chaotic sequence is related to the position of pixels. Chaotic table have a addresses of the pixel of two dimensional image. Binary encrypted image can be achieved as the chaotic se- quence by mathematical computation. Position of the pixel
(2)
stores sine energy values of an image. Sortrows of an image sine values in ascending order.
Acquire even feature vector of original medical image.
Empty the LSB for hiding the data. Even feature vector is cal-
culated by taking the mod of a two dimensional image.
Now scrambled the image by taking the difference between the image and mod image. Absolute the image for positive values.
The proposed algorithm flowchart
Fgure1. The diagram of watermarking algorithm with en- cryption by DST.
Decrypt the original watermarking image
The original image can be extracted from watermarked image.
Chaotic sequence can be deciphered with the private key. By
using HASH function of cryptography we can recover the
original watermarking image. Hidden information can be re-
store without any distortion which is large advantage to safety
of the medical image.
The Normalised cross-correlation(NC) is used to measure the
quantitative similarity between the extracted and embedded wa-
termarking which is defined as
where W denotes the embedded original watermarking and
w’ denotes extracted image. Higher the value of NC , more
will be the similarity between the extracted and original im-
age.
The peak signal to noise ratio is defined as:
(3)
where I(i,j), I’(i,j) denote the pixel value of coordinates(i,j) in the original image and watermarked image respectively .M,N represents the rows and the columns of pixel respectively.
To verify our proposed algorithm, we carried out are simula- tion in Matlab2011b platform. We have choosen medical im- age as original image (1≤i≤128,1≤j≤128).The size of the logical image (binary image) as(1≤i≤32,1≤j≤32).
Without any common attacks and geometric attacks the
difference between the embedded watermarking image and
original image is of ideal case. The quality of embedded image
has hardly any change.
1) When no attack
The encrypted image is the exact replica of original image.
Figure2: (a) Encrypted image (b) The Watermarked image without attacks.
The following are common attacks added to medical image.
2) Rotation attack
The rotation attack at 20 degree is added to watermarked im-
age to check the scheme is good robust against the common
attacks.This parameter helps to validate the effectiveness of
proposed algorithm.Figure3 shows that medical image is ro-
tated at 200.Furthermore, fig.(b) depicts that the watermarked
image can be extracted with NC=1.It proves that our proposed
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International Journal of Scientific & Engineering Research, Volume 4, Issue 8, August-2013 932
ISSN 2229-5518
algorithm has a strong robustness against rotation attack.
Figure3 .under rotation attack (200 ) (a) an image with rotation attack;(b)
the decrypted image.
(3) JPEG attack
The JPEG compression process is done by using a percentage of image quality as a parameter to measure. The medical im- age undergoes our proposed algorithm that is by discrete sine transform. Brain image with PSNR=40.3350 under JPEG attack
(8%) is shown in figure (a).Here decrypted image is extracted with NC=1.This shows that our scheme can resist against JPEG attack.
Figure4. under JPEG attack(8%) (a) an image under JPEG attack;(b) the decrypted watermarked image with NC=1.
(4) Median 3×3 attack
In a watermarked image, median filter (3×3) attack is added to
validate the effectiveness of our proposed algorithm. Figure
(a) shows that that medical image undergoes median attack.
Moreover fig(b) that watermarked image can be extracted
with NC=1. It states that there is similarity between the em-
bedded watermarking image and the original image and
hence proposed algorithm has strong robustness against me- dian(3×3) attacks.
Figure5. under Median 3×3 attack (a) an image under Median 3×3 at- tack;(b) the decrypted watermarked image with NC=1
TABLE I
Change of NC by DST to different attacks
No attack 0 Infinite 1
In this paper, encryption with DST achieves maximum degree of robustness against various attacks. we present an image encryption algorithm based on chaotic systems by discrete sine transform. The proposed algorithm has enough cipher key space to resist different kinds of attacks.It achieves maxi- mum degree of robustness in the encrypted data. Medical Images often are attacked by the noises and a series of other attacks in the transmission or other processes. From the de- crypted images, it can be seen that this algorithm has good anti-attack capability for the Rotation, JPEG compression and median filter. The algorithm has good encryption efficiency and safety seen from the simulation results.
I would like to thank Reecha Sharma from the Faculty of Elec- tronic Engineering UCoE, Punjabi University, Patiala for her efforts during the course of this work and the arrangement of this paper.
[1] Jiu-Lun FAN , Xue-Feng ZHANG1,2 ,” Image Encryption Algorithm Based on Chaotic System”.
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[4] Meghdad Ashtiyani, Parmida Moradi Birgani , Hesam M. Hosseini,” Chaos- Based Medical Image Encryption Using Symmetric Cryptography”.
[5] Shanshan Zhang, Xiaohong Wang, Shizheng Zhou, “The Research of Image Watermarking Encryption Algorithm ,”2011 Fourth international Joint Con- ference on Computational Sciences and Optimization,pp.821-824.
[6] Weiwei Xiao, Zhen Ji. Jihong Zhang. Weiying Wu, “A watermarking algo- rithm based on chaotic encryption,” Proceedings of IEEE Ten- con02,pp.545-548.
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Image Processing | MSE | PSNR | NC |
Original image | 0.0305 | 63.2940 | 1 |
Rotation(200) | 6.0606e+003 | 10.3056 | 1 |
JPEG compression | 6.0198 | 40.3350 | 1 |
Median filter (3×3) | 184.6567 | 25.4672 | 1 |
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