Essay: Dissertation: An integrated approach for visual cryptography schemes using compressed random shares

 
ABSTRACT
Visual cryptography is one of the most secure techniques that allows the user to encrypt the secret images by transforming them into printable transparent sheets and these sheets can be distributed to different intended person through various mediums (physically, internet). On receiving the intended person may regenerate the original image by stacking all transparent sheets on each other. There are many visual cryptography schemes available that facilitates user to encrypt and decrypt various type and formats of images. This thesis presents a visual cryptography scheme that can generate n number of transparent shares with reduced size and supports a variety of image formats and presents an integrated approach for binary, grey and color image visual cryptography by maintaining the good visual quality and minimal pixel expansion.
CHAPTER ‘ 1
1 INTRODUCTION
With the rapid advancement of internet, multimedia content is transmitted over the Internet conveniently. A number of secret information such as military orders and commercial prints are transmitted on the web. While using confidential images, security threats should be taken into consideration because hackers may utilize weak links over network to steal information that they want .To deal with the security problems of secret images, various image cryptography techniques have been developed. This work is an effort to extend the capabilities and useful implementation of these schemes.
1.1 Scope
The first Visual cryptography scheme was introduced by Noar and Shamir [5] in 1995. Visual cryptography is a cryptographic technique, which allows encryption of visual information like printed text, handwritten text and pictures in such a way that the decryption can be performed by the human visually, without knowing any help of computers. Visual cryptography scheme avoids heavy computation problem in decoding original image, and the secret images can be regenerated by stacking encrypted shares.
This feature makes visual cryptography especially useful for the low computation load requirement. This section presents an overview of various visual cryptography schemes and its applications. Taking limited bandwidth and storage into consideration two criteria pixel expansion and number of shares encoded is of importance. Less pixel expansion reduces size of encrypted share. Encoding multiple secret images into the same shares requires less overhead. Meaningful shares keep away from attention of hacker. To meet today’s multimedia requirements, gray and color image format should be encoded by secure schemes. Other performance factors such as contrast, accuracy, security and computational complexity that affect the efficiency of visual cryptography are also to be considered.
This thesis work is organized in four parts: part 1 provides overview of previous work done by various scholars, in part 2 the proposed methodology is discussed, in part 3, the system implementation is explained and last part analyses the results of the implementation. At last the conclusion and future work are presented.
1.2 Applications
VCS has many special applications, such as, transmitting military orders for soldiers, who may not have any cryptographic knowledge or computation devices in the battle ground. Many other applications of VCS, other than its original objective (i.e., sharing secret image), have been identified, for example, authentication and identification, transmitting passwords and watermarking etc. The associated secret sharing problem and its physical properties like contrast, pixel expansion, and color are broadly studied by researchers worldwide.
1.3 Objective of the thesis
The objective of this thesis is to design an application to provide construction and compression for secret images with random shares (transparencies) using half toning (for grey scale images) and LZW compression technique. This helps in maintaining better visual quality of the recovered secret image and at the same time also aims to provide the security mechanism for secret images.
1.4 Summary
One of the main challenges of the current image security systems is dealing with large amounts of data acquired by the modern modalities and maintaining the confidentiality of Images at the same time. Indeed, one of the most important demands toward dealing with image data is to provide a way for fast and secure data transmission over physical and electronic media. The most common approach toward enhancing the speed of data transmission is using compression techniques.
CHAPTER ‘ 2
2 LITERATURE SURVEY
The secret sharing problem and its properties such as contrast, pixel expansion, and color were broadly studied by researchers globally. For example, Naor et al and Blundo et al. proposed constructions of threshold VCS with perfect regeneration of the black pixels. Ateniese et al. showed constructions of VCS for the general access structure. Krishna et al and Liu et al. developed color VCSs. Shyu et al. suggested a scheme that can share multiple secret images [13]. Furthermore, Eisen et al. proposed a construction of threshold VCS for given whiteness levels of the recovered pixels.
All the VCS schemes are broadly categorized in following categories:
(i) Black and White VCS (Single / Multiple secret sharing)
(ii) Colored VCS (Single / Multiple secret sharing)
(iii) Extended VCS
(iv) VCS for general access structures.
These secret sharing schemes are discussed in subsequent sections
2.1 BLACK AND WHITE VISUAL CRYPTOGRAPHY SCHEMES
2.1.1 Sharing single secret
Naor and Shamir’s [5] proposed an encryption scheme to secure a binary image by converting it into two shares as shown in fig2.1. If pixel is white one of the above two rows of Table 1 is chosen to generate share (a) and Share (b). Similarly If pixel is black one of the below two rows of Table 1 is chosen to generate share (a) and Share (b). Each share pixel p is encoded into two white and two black pixels and every share alone reveal any information about the pixel p whether it is white or black. Secret image is revealed only when both shares are stacked on each other.
To hide a binary image into two meaningful shares Chin-Chen Chang et al [38] suggested an image hiding schemes based on spatial-domain. In this scheme two secret shares are embedded into two gray- level cover images. To decrypt the hidden messages, embedded covering shares can be superimposed. Liguo Fang [6] recommend a (2, n) scheme based on combination by Balancing the performance between pixel expansion and contrast. Threshold visual secret sharing schemes mixed XOR and OR operation with reversing and based on binary linear error- correcting code was suggested by Xiao-qing and Tan [16].
(a)
(b)
(c)
Figure 2.1 Basic VCS proposed by Naor & Shamir
The main drawbacks of the above schemes is that only one set of confidential messages can be embedded, so to share large amounts of confidential messages several shares have to be generated.
2.1.2 Sharing Multiple Secrets
The multiple secrets sharing technique in visual cryptography was proposed by S J Shyu et al [7]. This scheme encodes a set of n’ 2 secrets into two shares as a circle. The n secrets can be obtained one by one by stacking the first share and the by rotating second shares with n different rotated angles. To encode unlimited shapes of image and to remove the limitation of transparencies to be circular, Fang [8] suggested reversible VCS technique. In this suggested scheme two secret images that are encrypted into two shares; one secret image appears with just stacking two shares and the other secret image appears with stack two shares after reversing one of them. Jen-Bang Feng et al [9] developed a visual secret sharing scheme for hiding multiple secret images into two shares. This suggested scheme analyzes the secret pixels and the corresponding share blocks to construct a stacking relationship graph, in which the shared blocks are denoted by vertices and the edges denote two blocks stacked together at the desired decoding angle. Two shares are generated according to this graph and the pre-defined visual pattern set.
Wu and Chen [10] were first researchers to present the visual cryptography schemes to share two secret images in two shares. This scheme hides two secret binary images into two random shares, for example; A and B, such that the first secret can be seen by stacking the two shares, denoted by A??B, and the second secret can be obtained by first rotating A ?? anti-clockwise. They designed the rotation angle ?? to be 90′.
Figure 2.1 Pixel Distribution probability
However, it is easy to obtain that ?? can be 180′ or 270′. To overcome the angle restriction of Wu and Chen’s scheme [10], Hsu et al. [3] proposed a scheme to hide two secret images in two rectangular share images with arbitrary rotating angles. Wu and Chang [4] also refined the idea of Wu and Chen [10] by encoding shares to be circles so that the restrictions to the rotating angles (?? = 90′, 180′ or 270′) can be removed.
To provide more randomness for generating the shares Mustafa Ulutas et al [2] advised secret sharing scheme based on the share rotation. This scheme shares are rectangular in shape and are generated in an entirety random manner. Stacking of two shares reveals the first secret. By rotating the first share by 90?? counterclockwise and stacking it with the second share reveals the second secret. Tzung-Her Chen et al [11] offered the multiple image encoding VCS by rotating random grids, with no pixel expansion and codebook redesign. A no pixel expansion reversible visual secret sharing method that does not need to define the lookup table was offered by Fang [13]. To encode four secrets into two shares and recovering the reconstructed images without distortions Zhengxin Fu et al [14] intended a rotation VCS. Rotation visual cryptography scheme construction was based on correlative matrices set and random permutation basis, which can be used to encrypt four secret images into two shares. Jonathan Weir et al [15] suggested a scheme for sharing multiple secrets using visual cryptography. In this scheme, a master key is generated for all secrets; likewise, secrets are shared using the master key and multiple shares are regenerated.
All the above schemes can be used only to share the black and white images, but it is requirement of time that schemes should also support color images. To meet this requirement researches have been made efforts to share the color secret images.
2.2 COLOR VISUAL CRYPTOGRAPHY SCHEMES
2.2.1 Sharing Single Secret
Until the year 1997 visual cryptography schemes were applied to only black and white images. First colored visual cryptography scheme was developed by Verheul and Van Tilborg [17]. Colored secret images can be shared with the concept of arcs to construct a colored visual cryptography scheme. In this colorful visual cryptography scheme one pixel is converted into m subpixels, out of which, each subpixel is separated into c color areas. In each subpixel, there is exactly one color area colored, and all the other color areas are black. The color of one pixel depends on the relationship between the stacked subpixels. For a colored visual cryptography scheme with c colors, the pixel expansion m is c?? 3. Yang and Laih [18] improved the pixel expansion to c ?? 2 of Verheul and Van Tilborg [17]. But in both of these schemes share generated were meaningless.
For sharing a secret color image and also to generate the meaningful share for transmitting secret color image Chang and Tsai [19] anticipated color visual cryptography scheme. For a secret color image two significant color images are selected as cover images, which are the same size as the secret color image. According to a predefined Color Index Table, the secret color image will be hidden into two cover images. One drawback of this scheme is that extra space is required to build up the Color Index Table. In this scheme also number of subpixels is in proportional to the number of colors in the secret image as in Verheul and Van Tilborg [17] Yang and Laih [18] schemes.
When more colors are there in the secret image the larger the size of shares will become. To overcome this limitation Chin- Chen Chang et al [20] developed a secret color image-sharing scheme based on modified visual cryptography scheme. This scheme presents a more efficient way to hide a gray image in separate shares. The size of the shares in this scheme is fixed; it does not change when the number of colors appearing in the secret image differs. This Scheme does not require any predefined Color Index Table. Though pixel expansion is a fixed in [20] this scheme is not suitable for true color image. To share true-color image Lukac and Plataniotis [21] introduced bit-level based scheme by operating directly on S-bit planes of a secret image.
To hide a color secret image into multiple colored images it is desired that the generated camouflage images contain less noise. For this purpose R. Youmaran et al [22] invented an improved visual cryptography scheme for hiding a colored image into multiple colored cover images. This scheme provides improvement in the signal to noise ratio of the camouflage images by producing images with similar quality to the originals. For reducing pixel expansion in color visual cryptography scheme S.J. Shyu [23] advised a more efficient colored visual secret sharing scheme with pixel expansion of log2 c*m where m is the pixel expansion of the exploited binary scheme. For color image transmission over bandwidth constraint channels a cost effective visual cryptography scheme was invented by Mohsen Heidarinejad et al [24]. The solution offers perfect reconstruction while producing shares with size smaller than that of the input image using maximum distance separable. This scheme provides pixel expansion less than one.
For increasing the speed of encoding Haibo Zhang et al [25] presented a multi-pixel encoding which can encode variable number of pixels for each run. F. Liu et al [26] developed a color visual cryptography scheme under the visual cryptography model of Naor and Shamir with no pixel expansion. The increase in the number of colors of recovered secret image in this scheme does not increase pixel expansion. Wei Qiao et al [27] suggested visual cryptography scheme for color images based on halftone technique. A secret image-sharing scheme for true-color secret images was devised by Du-Shiau Tsai et al [40]. In the proposed scheme through combination of neural networks and variant VCS, the quality of the regenerated secret image and camouflage images are visually the same as the corresponding original images. For encoding multiple color images using visual cryptography little researches have been carried out that are discussed here.
2.2.2 Sharing Multiple Secrets
Tzung-Her Chen et al [12] proposed a multi-secrets visual cryptography, which is improved from traditional VCS. The codebook of conventional visual secret sharing was created to generate share images macro block by macro block in such a way that multiple secret images are turned into only two share images and decode all the secrets one by one by stacking two of share images in a way of shifting. This scheme can be used for multiple secret images with pixel expansion of 4.
Daoshun Wang et al [29] provided general construction for extended visual cryptography schemes using matrix extension scheme. A general creation method for single or multiple and binary, gray scale, color secret images using matrix extension utilizing meaningful shares was proposed. Using matrix extension scheme, any existing visual cryptography scheme with random-looking shares can be easily modified to utilize meaningful shares.
The basic principle of the visual cryptography scheme (VCS) was first introduced by Naor and Shamir. VCS is a secret sharing scheme that concentrates on sharing secret images. The idea of the visual cryptography scheme proposed in is to split a secret image into two random shares (printed on transparent sheets) which individually reveals no information about the secret image except the size of the secret image. The secret image can be regenerated by stacking the two shares. The basic operation of this scheme is logical operation OR.
In this work, we call a VCS with random shares the traditional VCS (Visual Cryptography Scheme). Normally, a traditional VCS takes a secret image as input, and generates secret shares as output that satisfies two conditions: 1) any qualified subset of shares can recover the secret image; 2) any banned subset of shares cannot obtain any information of the secret image other than the size of the secret image. An example of traditional (2,2)-VCS can be found in Fig. 1, where, a VCS means any out of shares could recover the secret image. In the scheme of Fig. 1, shares (a) and (b) are distributed to two intended users secretly, and each user cannot get any information about the secret image, but after stacking shares (a) and (b), the secret image can be seen visually by the users.
2.3 EXTENDED VISUAL CRYPTOGRAPHY SCHEMES
The term of extended visual cryptography scheme (EVCS) was first introduced by Naor et al. in [31], where a simple example of (2,2)-EVCS was presented. When we relate to a corresponding VCS of an EVCS, we mean a conventional VCS that have the same working with the EVCS. Normally, an EVCS takes a secret image and original share images as inputs, and generates shares that satisfy the following three conditions:
(i) Any qualified subset of shares can recover the secret image;
(ii) any forbidden subset of shares cannot obtain any information of the secret image other than the size of the secret image;
(iii) Generally, all the shares are meaningful images.
One scenario of the applications of EVCS is to avoid the routine inspections, because the shares of EVCS are meaningful images, therefore there are fewer chances for the shares to be detected. Many EVCSs have been presented in the literature. Droste [32], Ateniese et al. [33], and Wang et al. [29] developed three EVCSs, respectively, by manipulating the share matrices.
Nakajima et al. [34] proposed a (2,2)-EVCS for natural images. Tsai et al. [35] proposed a simple EVCS, where its shares were simply generated by replacing the white and black sub pixels in a traditional VCS share with transparent pixels and pixels from the cover images, respectively. Furthermore, Zhou et al. [37] presented an EVCS by using half toning techniques; it can handle gray-scale secret images. Their algorithms made use of the complementary images to cover share images. Recently, Wang et al. suggested three EVCS’s by using an error diffusion half toning technique to get nice looking shares. Their first EVCS also used complementary shares to cover the secret shares as the way proposed in [37]. Their second EVCS imported auxiliary black pixels to cover the secret shares. In such a way, each qualified user did not necessarily require a pair of complementary share images. Their third EVCS customized the half toned share images and imported extra black pixels to cover secret shares.
2.4 VCS for General Access Structure
VCS for general access structure with Multi-pixel encoding [8] is on of the emerging method in visual cryptography that can encode more than one pixel for each run. However, its encoding efficiency is not fast enough. This scheme offers a novel multi-pixel encoding that can encode variable number of pixels for each run. The encoding length at one run is equal to the number of the successive same pixels met during scanning the secret image. Proposed scheme works well for general access structure for chromatic images without pixel expansion. The experimental result shows that it can achieve high efficiency for encoding and good quality for overlapped images.
.
Sr.
No. Authors Year Number
of Secret
Images Pixel
Expa nsion Image Format Type of
Share
generated
1 Naor and Shamir [5] 1995 1 4 Binary Random
2 Verheul Tilborg [17] 1997 1 c*3 Color Random
3 Wu and Chen [10] 1998 2 4 Binary Random
4 Yang & Liah [18] 2000 1 c*2 Color Random
5 Chang and Tsai [19] 2000 1 529 Color Meaningful
6 Chin Chen Chang et al [20] 2002 1 9 Gray Meaningful
7 Hsu et al [3] 2004 2 4 Binary Random
8 Wu and Chang [4] 2005 2 4 Binary Random
9 Chin-Chen Chang et al [38] 2005 1 4 Binary Meaningful
10 Lukac and Plataniotis[21] 2005 1 2 Color Random
11 Liguo Fang et al [6] 2006 1 2 Binary Random
12 R.Youmaran et al [22] 2006 1 9 Color Meaningful
13 S.J.Shyu [23] 2006 1 log2 m*c Color Random
14 S. J. Shyu et al [7] 2007 n(n>=2) 2n Binary Random
15 W. P. Fang [8] 2007 2 9 Binary Random
16 Jen-Bang Fenget al[9] 2008 n(n>=2) 3n Binary Random
17 Mustafa Ulutas [2] 2008 2 4 Binary Random
18 Tzung-Her Chen et al in [11] 2008 2 1 Binary Random
19 Tzung-Her Chen et al[12] 2008 n(n>=2) 4 b, g, c Random
20 Mohsen Heidarinejad etal[24] 2008 1 16 Color Random
21 Haibo Zhang et al [25] 2008 1 1 Gray Random
22 F. Liu et al [26] 2008 1 1 Color Random
23 Wen-Pinn Fang [13] 2009 2 1 Binary Random
24 Zhengxin Fu[14] 2009 4 9 Binary Random
25 Jonathan Weir et al[15] 2009 n 4 Binary Random
26 Xiao-qing Tan [16] 2009 1 1 Binary Random
27 Wei Qiao et al [27] 2009 1 m Color Random
28 Du-Shiau Tsai et al [40] 2009 1 9 Color Meaningful
29 Feng Liu and C Wu [1] 2011 1 9 Gray Meaningful
30 S. J. Lin & W. H.Chung [41] 2012 1 1 Binary Random
Table 2.1 Brief Review of various VCS Schemes
2.6 Existing Systems
All the schemes discussed above have some noticeable drawbacks like large pixel expansion, low contrast etc. Most of above schemes support only one type of encryption scheme i.e. binary, grey or color. Existing applications supports only one kind of image formats
Proposed application supports .gif and .png (portable network graphics) formatted images and our application have been developed using Java technologies that provide a friendly interface to users. Table 2.1 provides a brief list of previous word done in the field of VCS.
2.7 Limitations of Existing Systems
The existing system provides specific cryptography schemes e.g. some provides VCS for binary images, some provides VCS for gray scale images and some provides VCS for color images by different methodologies and none of them provide a friendly interface to encrypt or decrypt the data (images).
2.8 Summary
The security implementation process in the proposed system consists of efficient and accurate algorithms to distinguish areas with and without textual information in digital or digitized images.
CHAPTER ‘ 3
3 PROPOSED SYSTEM
The proposed system provides a friendly interface to deal with secret images. Generally cryptography tools supports only one kind of image formats. Our application supports .gif and .png (portable network graphics) formatted images and our application has been developed using Java technologies that provides a friendly interface to users. Proposed VCS system is reasonably flexible for share pixel expansion and the visual quality of the shares and regenerated image.
This flexibility allows the dealer to choose the proper parameters for different applications. Experimental results of proposed system show that the visual quality of the share of the proposed VCS is competitive with many of the well-known VCSs in the literature.
Figure 3.1 Proposed System Architecture
The proposed system is implemented in four phases. In first phase the user interface is designed to interact with the user. In second phase visual cryptography scheme is implemented and integrated in the user interface. The encoding and decoding process is done in the third and fourth phases respectively.
3.1 User Interface Design
This is the first phase of the proposed system, in this phase we design user interface design using applet framework. The user interface is very easy and unambiguous to user. Anyone can access and create transparency and send them to the receiver using our system and it is supportable using designed GUI. The user interface also consists of help file. Interface assists on every concepts of the visual cryptography, it clearly depict the details of the system as it is developed in simple language.
3.2 Visual Cryptography Implementation
This module is the core of the proposed system, where we implement the Visual Cryptography. A well known LZW Data Compression algorithm is used to provide reduced size and data security. The LZW data compression algorithm is used for the gray scale image. A dictionary is prepared for the gray scale image. The string replaces characters with single quotes in this dictionary. Calculations are completed by dynamic Huffman coding. In compression of grayscale image, select the information pixels. Then produce halftone shares by error diffusion method. Finally filter process is applied for the output gray scale images. To improve the quality of regenerated image filters are used to minimize the noises for sharpening the input secret image.
3.3 Encoding
Encoding is done in three different phases for binary, grey scale and colored images to generate encrypted transparent shares. These encrypted shares are then reduced by applying LZW algorithm. The encoding for all the types are implemented as follows:
3.3.1 Binary Images
This cryptographic scheme is perfectly secure and can be encoded without any computations directly by the visual system. It conceals a picture by generating two transparent shares which look like random noise [5]. But overlaying of these transparencies leads to a clear image, which contains the original information for more possible schemes with more features look at the mode menu. Each pixel is divided into 4 sub pixels, which can be black or white. There are always 2 black and 2 white sub pixels. For displaying a white pixel, the sequence of the sub pixel on the first and on the second transparent share are identically Overlaying leads to 2 black and 2 white sub pixel. For displaying a black sub pixel the sequences of the sub pixel are different, so that you get 4 black sub pixels by overlaying.
3.3.2 Grey Scale Images
Proposed scheme can also handle grey scale images. This is done by using a well known technique called half toning. Half toning is the process of converting grey scale image to binary image [39]. After conversion, image may be encoded by using the same scheme used for binary scheme. The encoding scheme creates two transparencies for the visual cryptography with grayscales. The original picture is taken and for each pixel is decided which luminance it has. With this scheme, 4 different grayscales (white, light grey, dark grey, black) can be achieved. For each pixel there is decided which luminance it has and then a special matrix is assigned to it.
3.3.3 Color Images
Color images are encoded by defining some colors and deleting some colors through the overlaying process [18], whenever a black pixel is shown. For example:
red and black = black
and
red and red = red
This scheme creates two transparencies for the visual cryptography with colors. The original picture taken and for each pixel is decided which elementary color (red, green, blue or black) it has. Each pixel contains 1 red, 1 green, 1 blue and 3 black sub pixel. By overlaying the transparencies the black color dominates all others and is shown. For displaying a concrete color (for example red) all sub pixel except the red one overlayed with a black sub pixel. The red pixel is overlayed with a red sub pixel. So you achieve 5 black and a red sub pixel, and for the human visual system it appears as a (dark) red pixel.
3.3.4 General Access Structure
With this scheme you can generate 3 transparencies, whereas you can specify by the checkboxes (beside the original image) which group(s) of participants are allowed to decode [30]. For an application you can consider the example of a president and two generals. To fire a missile you need always president and one of the generals. So you would mark [President-1 and General-2] and [President-1 and & General-3] where 1 is the president, 2 and 3 are the generals. If all checkboxes are marked, then you get the same result as if you did a 2 out of 3 scheme. If no checkbox was selected then you get a 3 out of 3 scheme, since 2 participants are not privileged to decode.
3.3.5 Same Random Key Structure
This scheme shows the effect whenever a key is used two times for encryption [15]. It generates a random transparency serving as a key and then encrypts the right and the left image with a simple 2 out of 2 scheme. By overlaying the transparencies without the key you get a symmetrical difference and can achieve a lot of information about the two encrypted pictures. So what to do, only use a random key once (similar to a one-time-pad)”.
3.3.6 Compression
After the encoding, the encoded shares are compressed by using a well known technique called LZW compression [28]. A high level view of the LZW algorithm is shown here:
1. Initialize the dictionary to contain all strings of length one.
2. Find the longest string W in the dictionary that matches the current input.
3. Emit the dictionary index for W to output and remove W from the input.
4. Add W followed by the next symbol in the input to the dictionary.
5. Go to Step 2.
A dictionary is initialized to contain the single-character strings corresponding to all the possible input characters (and nothing else except the clear and stop codes if these are used). The algorithm works by scanning input string for successively longer substrings until it finds one that is not in the dictionary. If such a string is found, the index for the string less the last character (i.e., the longest substring that is in the dictionary) is retrieved from the dictionary and sent to output, and the new string (including the last character) is added to the dictionary with the next existing code. The last input character is used as the next starting point to scan for substrings.
3.4 Decoding
Decoding is a very simple process by reading a value from the encrypted input and producing the related string form the generated dictionary. During this the next value from the input is obtained and added to the dictionary by concatenation of the string and the first character of the string accessed by decoding the next value. This process is continued for the next input value and repeated the process until all inputs are finished. Decoder creates a dictionary that is identical to that used by the encoder; this dictionary is used to decode subsequent input values. The advantage of this scheme is that the full dictionary is not required to send with encoded data.
3.5 Creating Transparencies
This scheme provides supposedly perfect confidentiality. An attacker who accessed either the transparency image or the screen image cannot get any information at all about the encoded image as a black-white square on either image is equally likely to encode a clear or dark square in the original image. Another important property of VCS is that we can create the second layer after distributing the first layer to generate any image we want. Given a known transparent share image, we can select a screen image by selecting the proper squares to generate the desired image. One of the most noticeable limitations of using visual cryptography in the past was the difficulty of the decoded image containing an overall gray effect due to the extra black sub pixel from encoding. This happened because the decoded image is not a correct preproduction, but an expansion of original image, with extra black pixel. Black pixel in the original image remains black pixel in the decoded image, but White pixel becomes gray. This gives a lot of contrast to the entire image. The additional black sub pixel in the image leads the image to become distorted.
Divide data I (Secret Image) into n (Number of shares generated from I) pieces in such a way that I is easily reconstruct able from any N pieces, but even complete knowledge of any N-1 pieces reveals no information about I. Stacking two pixels (each consists of four sub-pixels) can occur for example the following two cases: Secret sharing scheme is a method of sharing secret information among a group of users. In a secret sharing scheme, each user gets a piece of secret image, called a share. When intended coalitions of the users pool their shares, they can recover the shared secret image; in other words, any other subsets, namely forbidden coalitions, cannot recover the secret image by pooling their share images. In the last decade, many secret sharing schemes have been proposed, but many of them need a lot of calculation to decode the shared secret information.
The basic 2 out of 2 VCS model consist of secret image encoded into two transparent shares, one transparent share representing the cipher text and the other acting as a secret key. Both transparent shares appear to be random dots when inspected individually and provide no idea about the original image. However, by careful alignment, the transparent shares, the original secret message is regenerated. The actual decoding is done by the human visual system. The original image is encrypted into 2 transparent shares; user needs both transparencies to decode the message.
3.6 Un-hiding Image from Transparency
The simplest form of visual cryptography divides an image into two layers so that either layer by itself gives no information about secret image, but when the layers are combined the image is displayed. One layer can be printed on a transparent share, and the other layer displayed on a monitor. When the share is placed on top of the monitor and aligned correctly, the image is shown. For each pixel of image, one of the two encoding options is randomly selected with equal probability. Then, the proper colorings of the share and screen squares are revealed based on the color of the pixel in the image.
3.7 Integration
This is the final phase, which consists of integration of Visual cryptography implementation developed in different phases into interface design using Java programming language. Then we need to test with various images and formation of transparent shares. The shares should be able to save and load into the user interface.
3.8 Advantages of Proposed System
Proposed scheme has many specific advantages against different well-known schemes that proposed scheme supports gray images and has smaller pixel expansion. This scheme is perfectly secure that nobody can find the actual image without having needed number of qualified shares. In the proposed scheme the covering shares images are not required and it also works for general access structures. One user only needs to carry one share.
CHAPTER ‘ 4
4 SYSTEM IMPLEMENTATION
4.1 Hardware Requirements
The proposed system is implemented with following Hardware Support
‘ System : Pentium IV 2.4 GHz.
‘ Hard Disk : 40 GB.
‘ RAM : 512 MB
‘ Monitor : 15’ VGA Colour.
‘ Mouse : Logitech.
‘ Ram : 512 Mb.
‘ Printer : Laser Printer
4.2 Software Requirements
The proposed system is implemented with following Software Support
‘ Operating System : Windows XP.
‘ Coding Language : JDK 1.6.
‘ Tools : Net beans 6.9
4.3 Functional Requirements
Functional requirements specify which output file should be produced from the given file they describe the relationship between the input and output of the system, for each functional requirement a detailed description of all data inputs and their source and the range of valid inputs must be specified.
4.4 Non Functional Requirements
Describe user-visible aspects of the system that are not directly related with the functional behavior of system. Non-Functional requirements include quantitative constraints, such as response time (i.e. how fast the system reacts to user commands.) or accuracy ((.e. how precise are the systems numerical answers.)
4.5 Pseudo Requirements
The client that restricts the implementation of the system imposes these requirements. Typical pseudo requirements are the implementation language and the platform on which the system is to be implemented. These have usually no direct effect on the user’s view of the system.
4.6 User Interface
The user interface of the proposed system is shown in Fig.4.1. The client that restricts the implementation of the system imposes these requirements. Typical pseudo requirements are the implementation language and the platform on which the system is to be implemented. These have usually no direct effect on the user’s view of the system.
Figure 4.2 User Interface of proposed system
4.6.1 Input Panel
This panel contains the secret image that is to be encrypted by selected scheme.
Initially there is a default image (LIOS.gif). User can load his own image by using File > Load image menu.
4.6.2 Encrypted Shares Panel
This panel shows all the transparencies generated by encrypting the secret image using selected VCS scheme. These shares are shown one by one using previous (<) and next (>) buttons.
4.6.3 Output Panel
This panel shows the output based on the selected number of shares by stacking one over another. The results depend on the number of shares generated by the VCS encryption scheme.
Figure 4.2 (a) File Menu, (b) Encryptor Menu (c) About Menu
4.6.4 File Menu
The user interface of the proposed system is shown in Fig.4.1. The client that restricts the implementation of the system imposes these requirements. Typical pseudo requirements are the implementation language and the platform on which the system is to be implemented. These have usually no direct effect on the user’s view of the system.
4.6.5 Encryption Mode Menu
The user interface of the proposed system is shown in Fig.4.1. The client that restricts the implementation of the system imposes these requirements.
Figure 4.3 Encryption Mode Menu
Typical pseudo requirements are the implementation language and the platform on which the system is to be implemented. These have usually no direct effect on the user’s view of the system.
4.6.6 Encryptor Menu
Encryptor menu provides the option to apply selected encryption scheme and encrypt the secret image loaded in the input panel. The generated encrypted transparencies are loaded in the Encrypted transparencies panel. These transparent shares are compressed using a well known LZW compression scheme and saved as .gif or .png image format.
4.6.7 About Menu
About menu provides details about the application and the scheme proposed in a submenu called about.
4.7 Summary
The system is implemented in such a way that it provides a very simple view to the user so that he can use it efficiently. Java Technology has enhanced the user experience in addition.
CHAPTER ‘ 5
5 RESULTS AND DISCUSSIONS
5.1 Images used for Implementation
The Images used in this project are shown in the Figure 5.1 below. The Images for VCS implementation are taken from the various research papers and other sites for the purpose of easy comparison of the quality of regenerated images using the proposed application. Size and the format of all the images is 225×225 and .jpg respectively
(a) LIOS
(b)LENA
(c) SHOMES
(d) QUESTION
(e) INDIA
(f) ITLY
Figure 5.1 Images used for implementation
Here comes the implementation part to see how the outputs look like. The secret image is loaded on the input panel and all the transparent shares are generated by selecting encryption option and placed in the encrypted panel. The results of regenerated secret image are shown in the result panel and it can be manipulated using the available checkboxes.
5.2 Results
Let’s see the implementation of some selected features of the proposed system.
Figure 5.2 Screenshots of Basic 2 out of 2 VCS
Figure 5.3 Screenshots of Basic 2 out of 3 VCS
Figure 5.4 Screenshots of Basic 3 out of 3 VCS
Figure 5.5 Screenshots of Basic 2 out of 2 Gray VCS
Figure 5.6 Screenshots of Basic 3 out of 3 Colored VCS
Figure 5.7 Screenshots of Basic 3 out of 3 with same random key VCS
Figure 5.8 Screenshots of Basic 3 out of 3 VCS with general access
5.3 Performance Evaluation
On the basis of the observations of various Images, the following results are observed:
5.3.1 Basic 2 out of 2 VCS Scheme for binary images
Image MSE ANALYSIS
Share 1 Share 2 Recovered
Image
Lios 7076.62 7168.98 7544.32
Question 2313.75 2350.96 2380.35
Sherlock 2175.76 2143.53 2809.90
Smile 2103.56 2180.66 1581.96
Table 5.1 MSE Analysis of binary images
Image SNR ANALYSIS
Share 1 Share 2 Recovered
Image
Lios 8.3294 8.2731 8.0514
Question 14.1167 14.0474 13.9935
Sherlock 14.2199 14.2847 13.1091
Smile 14.4724 14.3211 15.1980
Table 5.2 SNR Analysis of binary images
Image PSNR ANALYSIS
Share 1 Share 2 Recovered
Image
Lios 9.63 9.57 9.35
Question 14.48 14.41 14.36
Sherlock 14.75 14.81 13.64
Smile 14.90 14.74 15.62
Table 5.3 PSNR Analysis of binary images
5.3.2 Results of VCS Scheme for grey scale images
Image MSE ANALYSIS
Share 1 Share 2 Recovered
Image
LENA 9625.84 9583.11 9815.08
Monalisa 27376.9 27361.22 28406.3
Baboon 18551.18 18496.83 18773.55
Boat 16362.46 16423.40 16504.01
Table 5.4 MSE Analysis of Grey Scale images
Image SNR ANALYSIS
Share 1 Share 2 Recovered
Image
LENA 6.4516 6.4709 6.3671
Monalisa 2.3743 2.3718 4.5346
Baboon 1.8713 1.8841 1.8196
Boat 2.8716 2.8554 2.8341
Table 5.5 SNR Analysis of Grey Scale images
Image PSNR ANALYSIS
Share 1 Share 2 Recovered
Image
LENA 8.2964 8.3157 8.2119
Monalisa 3.7570 3.7594 3.5967
Baboon 5.4471 5.4598 5.3953
Boat 5.9923 5.9762 5.9549
Table 5.6 PSNR Analysis of grey scale images
5.3.3 Results of VCS Scheme for color images
Image MSE ANALYSIS
Share 1 Share 2 Recovered
Image
Italy 19893.00 19894.30 21809.70
Flag1 19189.20 19187.70 21554.10
Flag2 18176.10 18178.10 20394.00
Flag3 15115.30 15126.10 16157.80
Table 5.6 MSE Analysis of color images
Image PSNR ANALYSIS
Share 1 Share 2 Recovered
Image
Italy 5.17 5.17 4.77
Flag1 5.33 5.33 4.82
Flag2 5.56 5.56 5.06
Flag3 6.37 6.36 6.08
Table 5.6 PSNR Analysis of color images
5.3.4 VCS Scheme results for same / random key
S. NO IMAGE TYPE OF IMAGE MSE SNR PSNR
1 Question
&
lios question 2261.1591 14.2166 14.5875
lios 4342.0487 10.9279 11.7539
2 Question
&
Sherlock question 2260.1676 14.2185 14.5894
sherlock 9245.4246 7.0726 8.4715
Table 5.7 Analysis of VCS Scheme with same / random key
5.3.5 VCS Scheme results for general access
S. NO IMAGE TYPE OF IMAGE MSE SNR PSNR
1 LIOS Share 1 3933.1460 11.3574 12.1834
Share 2 3910.4130 11.3826 12.2086
Share 3 3933.3103 11.3572 12.1832
Recovered Image by S1 + S2 4228.1658 11.0433 11.8693
Recovered Image by S1 + S2 + S3 4498.8580 10.7738 11.5998
Table 5.8 Analysis of VCS Scheme for general access
5.4 Analysis of MSE and PSNR
There are two metrics that are used to compare different image processing methods. They are Mean Square-Error (MSE) and Peak Signal-to-Noise Ratio (PSNR). The cumulative squared error between the original and the compressed image is shown by MSE and the peak error is shown by the PSNR. Mathematically, they are written as follows,
And
Where I(x,y) denotes the original image and I'(x,y) denotes the approximation to the original image which is also called as the decompressed image. M, N is the image dimensions.
The lower value of MSE says that the errors are less. Due to inverse relation of MSE and PSNR, the errors will be less when the PSNR is high. Logically, signal is the image and noise is the errors produced in the reconstructed image. So, if signal to noise ratio is peak and MSE is less for an image when comparison then one can make a confirmation that this is the better one. The term PSNR is an engineering term for the ratio of the maximum possible power of the signal to the power of corrupting noise that affects the fidelity of its representation. Since many signals have a wide dynamic range, PSNR is expressed in logarithmic decibel scale.
PSNR is the measure of the quality of reconstruction of the compressed image. It can be easily defined through the MSE which for two m X n monochrome images I and K where one of them is assumed as the noisy approximation to the other and is defined as,
The PSNR is defined as:
The maximum possible pixel value is defined by MAX I .When the pixels are 8 bits per sample then it is 255. (i.e) if the pixels are represented by PCM with B bits per sample then MAX I is 2B- 1.
The color images have three RGB values per pixel, for which the PSNR is defined as the same except the Mean Square-Error (MSE) is the sum over all squared value differences divided by image size and by three. Typically, in lossy image and video compression, the PSNR values are from 30 to 50 dB, where higher is always better for PSNR.
5.5 Comparative Analysis
According the collection of data from various schemes, proposed scheme provides competitive visual quality and pixel expansion of encrypted secret image. The noble feature is that it provides an integrated interface for all binary, grey and color visual cryptography at single place.
The common parameters that effect visual quality and security like pixel expansion, number of share generation, and size of generated shares etc. have been tested and observations shows that proposed scheme maintains these parameters competitive with previously proposed schemes in following manner:
(i) No extra pixel expansion occurs such that the proposed scheme does not worsen the drawback of traditional VSS.
(ii) Since, the proposed scheme can be used to encode not only binary images but also gray-level or color images that the present scheme is, thus, of wide use.
Proposed scheme have pixel expansion of 4 in normal case, the type of shares generated are random and square and it supports wide image format (binary, grey and color images). By comparing with table 2.1, it can be easily observed that proposed scheme provides very competitive features.
Following results have been observed for binary images:
PSNR ANALYSIS
Scheme Share 1 Share 2
Wang[29] 3.19 3.77
Zhao[37] 9.54 0.51
ZM Wang[42] 3.16 4.08
ZM Wang[42] 4.62 4.11
Proposed 8.29 8.31
Table 5.9 PSNR comparison of some well known schemes
5.6 Summary
The results found in previous sections shows that the proposed scheme is very competitive with other well known schemes found in literature. In addition, proposed scheme provides all VCS schemes for binary, gray scale and color secret images under the single application to get the benefit of it.
CHAPTER ‘ 6
6 CONCLUSION AND FUTURE WORK
6.1 Conclusion
In this thesis, the VCS construction is proposed which was generated to secure the secret image by dividing it into the random shares. The proposed system fulfils the requirement to secure a secret image with required level of security and size limitations. After implementation of proposed system, it is concluded that:
‘ The shares of the proposed scheme are random images, and the stacking of a qualified subset of shares will recover the secret image visually.
‘ According to comparisons with many of the well-known EVCS in the literature the proposed scheme has many specific advantages against different well-known schemes that proposed scheme supports gray images and has smaller pixel expansion.
‘ This scheme is perfectly secure in the sense that nobody can find the actual image without having required number of qualified shares.
‘ In the proposed scheme the complementary shares images are not required and it also works for general access structures. One participant only needs to carry one share.
Furthermore, the proposed system is very easy to use and anybody can use this system without having any cryptographic knowledge. This system can be used in both ways i.e. shares can be printed on the transparent sheet and carried by users or it may be transmitted by the network and secret image may be regenerated by the system using required number of qualified shares.
6.2 Future Work
The proposed system is competitive with some well known visual cryptography schemes and it also provides a user friendly environment for the implementation of the system. This system produces reasonable quality of reproduced secret images which can further be improved.
CHAPTER ‘ 7
7 REFERENCES
[1] Feng Liu and Chuankun Wu, ‘Embedded Extended Visual Cryptography Schemes’, IEEE TRANSACTIONS ON INFORMATION FORENSICS AND SECURITY, VOL. 6, NO. 2, JUNE 2011.
[2] Mustafa Ulutas, R??fat Yaz??c??, Vasif V. Nabiyev, G??zin Ulutas, (2,2)- ‘Secret Sharing Scheme With Improved Share Randomness’, 978-1-4244-2881-6/08, IEEE, 2008.
[3] H.-C. Hsu, T.-S. Chen, Y.-H. Lin, ‘The Ring Shadow Image Technology Of Visual Cryptography By Applying Diverse Rotating Angles To Hide The Secret Sharing’, in Proceedings of the 2004 IEEE International Conference on Networking, Sensing & Control, Taipei, Taiwan, pp. 996’1001, March 2004.
[4] H.-C. Wu, C.-C. Chang, ‘Sharing Visual Multi-Secrets Using Circle Shares’, Comput. Stand. Interfaces 134 (28) ,pp. 123’135, (2005).
[5] Moni Naor, Adi Shamir, ‘Visual Cryptography’, advances in cryptology’ Eurocrypt, Berlin, Germany, 1995, vol. 950,pp 1-12. Springer-Verlag, LNCS.
[6] Liguo Fang, BinYu, ‘Research On Pixel Expansion Of (2,n) Visual Threshold Scheme’, 1st International Symposium on Pervasive Computing and Applications ,pp. 856-860, IEEE. 2006.
[7] S. J. Shyu, S. Y. Huanga,Y. K. Lee, R. Z. Wang, and K. Chen, ‘Sharing multiple secrets in visual cryptography’, Pattern Recognition, Vol. 40, Issue 12, pp. 3633 – 3651, 2007.
[8] Wen-Pinn Fang, ‘Visual Cryptography In Reversible Style’, IEEE Proceeding on the Third International Conference on Intelligent Information Hiding and Multimedia Signal Processing (IIHMSP2007), Kaohsiung, Taiwan, R.O.C, 2007.
[9] Jen-Bang Feng, Hsien-Chu Wu, Chwei-Shyong Tsai, Ya-Fen Chang, Yen-Ping Chu, ‘Visual Secret Sharing For Multiple Secrets’, Pattern Recognition 41 ,pp. 3572 ‘ 3581, 2008.
[10] C.C. Wu, L.H. Chen, ‘A Study On Visual Cryptography’, Master Thesis, Institute of Computer and Information Science, National Chiao Tung University, Taiwan, 1998.
[11] Tzung-Her Chen, Kai-Hsiang Tsao, and Kuo-Chen Wei, ‘Multiple-Image Encryption By Rotating Random Grids’, Eighth International Conference on Intelligent Systems Design and Applications, pp. 252-256 , 2008.
[12] Tzung-Her Chen, Kai-Hsiang Tsao, and Kuo-Chen Wei, ‘Multi-Secrets Visual Secret Sharing’, Proceedings of APCC2008, IEICE, 2008.
[13] Wen-Pinn Fang, ‘Non-Expansion Visual Secret Sharing In Reversible Style’, IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.2, February 2009.
[14] Zhengxin Fu, Bin Yu, ‘Research On Rotation Visual Cryptography Scheme’, International Symposium on Information Engineering and Electronic Commerce, pp 533-536, 2009.
[15] Jonathan Weir, WeiQi Yan, ‘Sharing Multiple Secrets Using Visual Cryptography’, 978-1-4244-3828-0/09, IEEE, pp 509-512, 2009.
[16] Xiao-qing Tan, ‘Two Kinds of Ideal Contrast Visual Cryptography Schemes’, International Conference on Signal Processing Systems, pp. 450-453, 2009.
[17] E. Verheul and H. V. Tilborg, ‘Constructions And Properties Of K Out Of N Visual Secret Sharing Schemes.’ Designs, Codes and Cryptography, 11(2) , pp.179’196, 1997.
[18] C. Yang and C. Laih, ‘New Colored Visual Secret Sharing Schemes’. Designs, Codes and cryptography, 20, pp. 325’335, 2000.
[19] C. Chang, C. Tsai, and T. Chen. ‘A New Scheme For Sharing Secret Color Images In Computer Network’, Proceedings of International Conference on Parallel and Distributed Systems, pp. 21’27, July 2000.
[20] Chin-Chen Chang, Tai-Xing Yu , ‘Sharing A Secret Gray Image In Multiple Images’, Proceedings of the First International Symposium on Cyber Worlds (CW.02), 2002.
[21] R. Lukac, K.N. Plataniotis, ‘Bit-Level Based Secret Sharing For Image Encryption’, Pattern Recognition 38 (5), pp. 767’772, 2005.
[22] R.Youmaran, A. Adler, A. Miri , ‘An Improved Visual Cryptography Scheme For Secret Hiding’, 23rd Biennial Symposium on Communications, pp. 340-343, 2006.
[23] S.J. Shyu, ‘Efficient Visual Secret Sharing Scheme For Color Images’, Pattern Recognition 39 (5) ,pp. 866′ 880, 2006.
[24] Mohsen Heidarinejad, Amirhossein Alamdar Yazdi and Konstantinos N, Plataniotis ‘Algebraic Visual Cryptography Scheme For Color Images’, ICASSP, pp. 1761-1764, 2008.
[25] Haibo Zhang, Xiaofei Wang, Wanhua Cao, Youpeng Huang , ‘Visual Cryptography For General Access Structures By Multi-Pixel Encoding With Variable Block Size’, International Symposium on Knowledge Acquisition and Modeling, pp. 340-344, 2008.
[26] F. Liu, C.K. Wu X.J. Lin , ‘Colour Visual Cryptography Schemes’, IET Information Security, vol. 2, No. 4, pp 151-165, 2008.
[27] Wei Qiao, Hongdong Yin, Huaqing Liang , ‘A Kind Of Visual Cryptography Scheme For Color Images Based On Halftone Technique’, International Conference on Measuring Technology and Mechatronics Automation 978-0-7695-3583-8/09, pp. 393-395, 2009.
[28] Welch, Terry, “A Technique for High-Performance Data Compression”. 0018-9162/84/0600-0008, IEEE, June, 1984.
[29] Daoshun Wang, FengYi, XiaoboLi, ‘On General Construction For Extended Visual Cryptography Schemes’, Pattern Recognition 42 (2009),pp 3071 ‘ 3082, 2009
[30] Giuseppe Ateniese, Carlo Blundo, Alfredo De Santis, Douglas R. Stinson, ‘Visual Cryptography for General Access Structures’, Information and Computation 129, 86-106, 1996.
[31] M. Naor and A Shamir, ‘Visual Cryptography’, in Proc. EUROCRYPT’94, Berlin, Germany, 1995, vol.950,pp. 1-12, Springer-Verlag,LNCS.
[32] S. Droste, ‘New results on visual cryptography,’ in Proc. CRYPTO’96,1996, vol. 1109, pp. 401’415, Springer-Verlag Berlin LNCS.
[33] G. Ateniese, C. Blundo, A. De Santis, and D. R. Stinson, ‘Extended capabilities for visual cryptography,’ ACM Theoretical Comput. Sci.,vol. 250, no. 1’2, pp. 143’161, 2001.
[34] M. Nakajima and Y. Yamaguchi, ‘Extended visual cryptography for natural images,’ in Proc. WSCG Conf. 2002, 2002, pp. 303’412.
[35] D. S. Tsai, T. Chenc, and G. Horng, ‘On generating meaningful shares in visual secret sharing scheme,’ Imag. Sci. J., vol. 56, pp. 49’55, 2008.
[36] Daoshun Wang, FengYi, XiaoboLi, ‘On General Construction For Extended Visual Cryptography Schemes’, Pattern Recognition 42 (2009),pp 3071 ‘ 3082, 2009.
[37] Z. Zhou, G. R. Arce, and G. Di Crescenzo, ‘Halftone visual cryptography’, IEEE Trans. Image Process., vol. 15, no. 8, pp. 2441’2453,Aug. 2006.
[38] Chin-Chen Chang, Jun-Chou Chuang, Pei-Yu Lin, ‘Sharing A Secret Two-Tone Image In Two Gray-Level Images’, Proceedings of the 11th International Conference on Parallel and Distributed Systems (ICPADS’05), 2005.
[39] C. C. Lin, W. S. Tsai, ‘Visual cryptography for gray-level images by dithering techniques’, Pattern Recognit. Lett., vol 24, no 1-3, pp 349-358, 2003.
[40] Du-Shiau Tsai , Gwoboa Horng , Tzung-Her Chen , Yao-Te Huang , ‘A Novel Secret Image Sharing Scheme For True-Color Images With Size Constraint’, Information Sciences 179 3247’3254 Elsevier, 2009.
[41] S. J. Lin and W. H. Chung, ‘A Probabilistic Model of (t,n) Visual Cryptography Scheme With Dynamic Group.’, IEEE Transactions, Vol. 7, No.1, Feb.2012.
[42] Z.M.Wang, G. R. Arce, and G. Di Crescenzo, ‘Halftone visual cryptography via error diffusion,’ IEEE Trans. Inf. Forensics Security, vol.4, no. 3, pp. 383’396, Sep. 2009.
PAPERS PUBLISHED
[1] L. N. Pandey, Neeraj Shukla, ‘Visual Cryptography Schemes Using Compressed Random Shares ‘, International Journal of Advance Research in Computer Science and Management Studies Volume 1, Issue 4, pp. 62 ‘ 66,Sep 2013.
[2] L. N. Pandey, Mukta Bhatele, ‘Visual Cryptography Schemes: A Comparative Survey’, Volume 1 Issue 2. pp. 34 ‘ 40, in International Journal of Modern Engineering & Management Research, July 2013.
[3] L. N. Pandey, Mukta Bhatele, ‘Online Social Networks: A Survey on Security Challenges’, National Conference on Emerging Trends in Computational Science. MANIT, Bhopal (MP) 8-9th March 2013.