A SECURE AND EFFECTIVE ALGORITHM FOR VIDEO VISUAL
CRYPTOGRAPHY
1Maya Chouksey,2Prof.Shanu K. Rakesh
1M.Tech. Scholar,2Asst.Professor 1Department of CSE,2Department of CSE
1Chouksey Engineering College,2Chouksey Engineering College, Bilaspur, India
Abstract
Conversion of visual information such as any text, picture, image, hand written notes or even video into a encrypted forms which can only be decrypted by human visual system instead of computer based algorithm is called visual cryptography system. Since long attempt has been made to encrypt the data which can be decrypted with least computational cost or without the application of computer. In this paper author has attempted to devise efficient and effective method of visual cryptography which can be used to encrypt the color image visually. This method is efficient in the sense that it can be able to encrypt multiple image in a single image. Various parameters for performance analysis also reveal the effectiveness and security of this scheme.
Keywords: visual cryptography scheme (VCS), pixel expansion, accuracy,
contrast-level, security, computational complexity. (VCS), pixel expansion, contrast-level, security, accuracy, computational complexity.
I. INTRODUCTION
The rapid advancement in the communication technology in last decades has made the high speed and error free communication possible. Each and every organization is now seeking this opportunity to communicate with each other using this technology.
In the last couples of years, lot of work has been done to improve the performance of electronics communication. Two major areas where significant improvement has been done are error free communication and achieving high speed communication. Now, with high
speed data transfer techniques, it is possible to send even multimedia based information error free and great speed. Military organization in various countries also using these techniques to send confidential information across the world which include confidential and secret information , data and maps. Apart form military organization, various other organization also send their confidential information to other organization in the world.These information goes through the internet and internet is open to all. Such kind of confidential information can also be leaked from here and put the organization and country under the threat.
It is very important to secure such confidential information before sending them across the world via internet.Often confidential information includes videos and images. For protecting such kind of information various secret image sharing techniques have been proposed and developed in the last decades.
are first encrypted and encryption process is applied in such a way that decryption process does not need any kind of computational complexity. In fact , in visual cryptography, a simple stack operation is used for decryption purpose making it free from any kind of complex computation. Low computational cost is one of the most important advantage of this scheme and makes it very useful for low computational requirement.
The history of visual cryptography began from the scheme of Naor and Shamir[1]. They proposed a scheme which shared the image of binary format in to two secret
shares i.e. share1 and share2.
Superimposing these two secret shares reveals the secret image. Disadvantage of this scheme is that its generated shares are meaningless.
Chin-chen Chang et al [5] developed schemes which can generate two meaningful shares which contain the secret image within the shares. In his scheme, secret image is hidden by using the spatial domain method. Two gray level images are taken to hide the shares generated in this sheme.
Liguo Fang [6], proposed a method of visual cryptography which was based on the pixel expansion method and contrast level manipulation.
Xiao-qing and Tan [16] introduced XOR and OR operation based visual secret sharing scheme. This scheme also made use of binary correcting code for getting back the secret image.
Wu and Chen [2], first introduced multiple
secret sharing scheme they successfully generated two shares for two secret images. This scheme generates two randomly generated shares from the two secret images. Image rotation and XOR operation is used in their scheme for encryption purpose. Two drawback of this scheme is that it is used only for black and white image and limited angle of rotation. Wu and Chen [2], introduced a method of visual cryptography which is free from angle restriction generating two rectangle shares of two secret images by having any rotating angle.
pixel expansion effect. Zhengxin Fu et al [14] came up with the idea of another rotation based visial cryptography scheme. This scheme first encode the four secrets into two different shares. This scheme was able to reconstruct the image without any distortion. Correlative matrix is used in most of the rotation based visual cryptography scheme along with the random permutation for converting the four secrets in to two different shares.Master key based secret sharing scheme was was introduced by Jonathan Weir et al [15].
Secret sharing schemes for color image was first proposed by Verheul and Van Tilborg [17], which was based on the concept of arcs. Later on an improved version of color image based secret sharing scheme was introduced by Yang and Laih [18].
Chang and Tsai [19] introduced another scheme which is able to create meaningful shares of the color image to be transmitted.
Comparatively more efficient scheme was proposed by Chin-Chen Chang et al [20]. Lukac and Plataniotis [21] , later on introduced the scheme good for true color image.Some other notably contribution were proposed in this field by R.Youmaran et al [22], S.J.Shyu [23], Mohsen Heidari nejad et al[24], Haibo Zhang et al [25], F. Liu et al [26], Wei Qiao et al [27], Du-Shiau Tsai et al [28].Some other noteworthy contribution in multiple sharing schemes were introduced by Tzung-Her Chen et al [12], Daoshun Wang et al [29],
IV. PROPOSED METHODOLOGY
In this work, a new scheme of video visual cryptography is presented. This scheme is able to encrypt the video using video visual cryptography. In this scheme two different encryption algorithm is applied after carrying out the visual cryptography operation in the video. The purpose of using two more encryption method is basically to enhance the security of the visual cryptography.
[image:3.595.321.580.361.630.2]The block diagram approach of this scheme is shown in the figure given below.
Figure 4.1 Block Diagram of the proposed Method
A. Steps of algorithm for Video Visual Cryptography.
Step2- Get the number of frames of video. Step3 – Convert video into frame by applying the filter for Red, green and blue channel.
Step4- Apply visual crypto scheme among Red frames of secret video and random video.
Step5- Apply visual crypto scheme among Green frames of secret video and Random video.
Step6- Apply visual crypto scheme among Blue frames of secret video and Random video.
Step7- With the help of key1 apply random pixel shifting scheme of Red frames obtained in the step6.
Step8- Similarly with the help of same key1 apply random pixel shifting scheme on green frames obtained in step6 . Step9- with the help of secret key1, encrypt the blue frame of secret video by applying the random pixel shifting scheme.
Step10- Apply chaos based encryption scheme to the encrypted red channel obtained in step 7 by using key2.
Step11- Apply Chaos based encryption scheme to the encrypted green channel obtained in step8 by using key2. Step12- Apply the Chaos based
encryption scheme to the encrypted blue channel obtained in step 9 by using key2.
Step13- Combine all the double
encrypted Red, green and blue channel to form the crypto frames.
Step14- Convert the crypto frames to video to get the encrypted video.
This phase of the encryption algorithm gives one random video and one crypto video. These two video then can be sent to the desired location at different times. Both the video along with the key1 and key2 only make any one able to decipher the secret video.
B. Steps of algorithm for generating the visual cryptography
frames-Step1- Get the secret video and convert it into a frames.
Step2- Get the Random video and convert it also into frames.
Step3- Apply the XOR operation to get the cryptographic frames or two different shares i.e. share1 and share2.
encryption scheme is applied to enhance the security.
C Steps of algorithm for Chaos based encryption scheme.
Step1- Input the Encrypted frame one by one .
[image:5.595.77.275.230.554.2]Step2- Obtain the dimension (row and column) of current frame, i.e. a,b.
Figure 4.3 Block Diagram of Chaos Algorithm
Step3- Now let N=axb and input the value of m=0.4 ( work as key2)
Step4- Now obtain the new value of m by using below operation.
m(i+1)=4*m(i)-4*m(i)^2 for all N. Step5- Now obtain the new value of m by m= mod(1000*m,256) where m are the value obtained in the step 4.
Step6- Apply the XOR operation between m and every pixel of current frame to get the encrypted frame.
D Steps of Algorithm Steps for Decryption Scheme
Step1- Get the crypto video share i.e. share1 video and share2 video.
Step2- Convert these share videos into frames.
Step3- Apply the Chaos based decryption method on the frames found in step2 to get the decrypted frames using key2. Step4- Apply the reverse of random shifting operation to obtain the decrypted Frames obtained in the step 3.
Step5- Get the Random video and convert in to frames.
Step6- Apply the Visual cryptography scheme on the frames produced at the step4 and step5 to get back the original frames of the secret video.
Step7- Apply frame to video conversion algorithm to get back the secret video.
Figure 5.1 Histogram Analysis
Histogram analysis, correlation coefficient analysis, entropy analysis, plain image sensitivity, Key sensitivity analysis has been performed for checking the effectiveness of this algorithm.
A. Histogram Analysis
Histogram is one of the tool to analyze the security strength of the encryption algorithm. Histogram is basically the
graph between the number of pixel versus intensity level of the pixel. For a strong encryption algorithm, the histogram of encrypted share frame and original video frame must be different and the histogram encrypted share frame must be similar. In this figure 5.1(a) shows the secret video, 5.1(b) shows the random video. Figure 5.1(c) and figure 5.1(e) shows the original video frames of two video share while figure 5.1(d) and 5.1(f) shows the corresponding histogram of figure 5(c) and 5.1(e). figure 5.1(g) and figure 5.1(i) shows the encrypted video share and their corresponding histogram is shown in the figure 5.1(h) and 5.1(j).
From these figure it is clear that the histogram of original and encrypted frames are different but histogram of encrypted frames are similar.
B. Correlation Coefficient Analysis
In this formula, x and y represent the gray scale pixel value of two adjacent pixel in the image.
Table 5.1 Correlation coefficient between Original and Encrypted Frame
The value of correlation coefficient for the pixel among the original frames is very close to 1 which signifies strong correlation between the pixels of original frames. While the correlation value is very close to 0 among the pixels of encrypted frame, which signifies that there are lmost no correlation among the pixels of the encrypted frames and hance encrypted image bear very high randomness among their pixels.
C. Plain Image Sensitivity
Plain image sensitivity means resistance offered by the cipher to differential attacks.
NPCR and UACI test are used for this kind of analysis. Basically NPCR and UACI metrics are used to check the number of changing pixel in cipher image and also averaged changed intensity among the encrypted images considering very subtle change in plain image.
In order to understand how these metrics works, lets consider plain image and its corresponding cipher image and if Ip represent the plain image and Icip represent the cipher image, if there is a array called U whose size is same as that of plain image then U is defined as
U(i,j)=0 if Ip(i,j)=Icip(i,j)
U(i,j)=1, Otherwise
So NPCR can be given as
So from this formula it is clear that NPCR gives the percentage of number of pixel which are different in plain image and the cipher image.
This scheme of visual cryptography in video is able to achieve over 98% and UACI over 35% which clearly give the indication that this method is very sensitive to even small pixel change in plain image.
Table 5.2 NPCR and UACI Metrics for Selected video
Video Name Frames NPCR(in %) UACI(in
%) Newsreader.avi Share 1
and Encrypted share1
99.5722 40.002
Share2 and Encrypted share2
99.5285 35.6133
D. Key Sensitivity
Any encryption algorithm is considered to be the ideal one if it is very sensitive to a little change in the key i.e a very small change like one bit change in the key may lead to a totally different outcome. In this analysis, a one bit change in the key was made deliberately and then encrypted frames was then decrypted with this change key. The decrypted frame obtained with this changed key was found to be totally different from the original video frame. Video frames generated with original key and the changed key is shown in the figure 5.2(a) and 5.2(b). the results
[image:8.595.318.520.148.340.2]obtained for two different key are found to be totally different.
Figure 5.2 Key Sensitivity
5.2 (a) and (b) shows the video share obtained from original and the changed key. While the figure 5.2 (c) and (d) shows the encrypted frame obtained by original key and the changed key.
E. Entropy Analysis
Entropy is given by the following formula
data. Table 5.3 shows the entropy value for the encrypted frames.From the table, we can see that the value is very close to 8 for the encrypted image.
Table 5.3 Entropy for original and encrypted frames
V. CONCLUSION
In this work, visual cryptography of image has been taken to the next level by applying this scheme on the color video. In this project work MATLAB platform is used for implementation of this scheme.
Experimental results shows that the scheme present in this project work is capable of performing the encryption –decryption operation very effectively.
Various kind of analysis and parameter reveals the efficiency and effectiveness of this scheme in the frontier of encryption.
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