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Visual Information Encryption

Visual Information Encryption

Abstract

Visual cryptography provides secured digital transmission which is used only for one time. In order to make visual cryptography reusable Diffie and Hellman (D-H) key is used. The original images can be reuse by using this scheme. It is effortless and uncomplicated technique to execute the secret image for shadow images. The shadow images are the shrunken version of the original image, in which the secret image share is embedded. These are used to guard the data and secret images in the internet so that it is not accessed by any unauthorized persons. Visual cryptography divides the image into secret shadow images. After this these shadow images are distributed in the original image. Recovering of secret image is done by human visual system by piling all the shadow images. As this Visual cryptography is used only once D-H key agreement was used to make it reusable by using D-H key scheme in it.

Objectives:

* Provision of security for hidden images

* Reusing of the original image is possible by this technology

* Images should be visible only to human visual system

Literature Review

In this project a visual cryptography scheme is used for encrypting the information. Visual cryptography is an encryption method which is used to hide the information in an image, decrypted can be done by human visual system. By using only this scheme the reusing is not possible. The image which is recovered after decryption will not be same as original image so it cannot be reused. For the reuse of the visual cryptography Diffie and Hellman (D-H) key agreement method and Toral Automorphism (TA) can be used. In this both secret and symmetry-key representation can be used (Chao-Wen Chan and Yi-Da Wu, 2008). Visual cryptography is the scheme which facilities the secret sharing of the pictures or data. The pixels of the pictures or data that need to be transmitted secretly will be treated as an individual secret which can be shared using a secret sharing scheme. The picture is first split into two or more shared images the secret data are embedded. At the decryption side images are joined on the transparent paper to get the secret picture or data. This is the way in which the first visual cryptography was started (Borivoje Furht, Edin Muharemagic and Daniel Socek, 2005). Using current methods the Visual cryptography scheme will allow the encoding of the secret image into shares; this is done in the form of transparencies. These shares are distributed to the participants, such that only the qualified subsets of participants can recover the secret image visually. This is done by superimposing the share images one over the other which are obtained from the original image (Carlo Blundo and Stelvio Cimato, 2005). In this scheme the devices are used for encoding of secret information and the decoding is done with human vision directly. For encoding, the visual cryptography will cryptographically encode the binary secret data into shares of the pattern which will be random. Then the shares are copied on to the transparencies with the same number of transparencies as shares. The transparencies are distributed among the participants, one for each participant. The decoding of the data or picture is done only when all of the participants superimpose their transparencies (Alan Conrad Bovik, 2005). The importance of this scheme is that there is no need for data expansion. The resolution of the data will not be lost by using this scheme. By using this scheme the image will be secure against the most important cryptanalytic attacks. The computation complexity will be less since it involves only XOR operations. By using XOR operations the share images are combined to form the encrypted images. The authentication of the image will be based on the global visual effect, so local defects due to noise will not affect the final result. The most important aspect of this scheme is that the decoding of the secret data or image can be done with human vision without any decoding equipment (Kiyoharu Aizawa, Yuichi Nakamura and Shinichi Satoh, 2004). The previous technologies that came into existing before visual cryptography are two-out-of two visual threshold schemes, two-out-of-n visual-threshold scheme. In a two-out-of two visual threshold scheme the secret can be any type of data (Abhishek Parakh and Subhash Kak, 2006, p.1). For an image comprising of white and black pixels, this image can be encoded as a binary string. In this scheme the 0 will represent a white pixel and 1 represents a black pixel and the result will be sent in two shares. The security problem by this is having only 50 percent of resolution will be obtained because the image is divided into only two shares and if the new shares of data are found the image can be decrypted very easily. A two-out-of-n visual-threshold scheme is more secure when compared with the first. In this scheme also the pixels are divided into two, but the shares will be ‘n'. By this the security will increase. When compared with the D-H key agreement the resolution of these schemes will be less and security will also be less (Doug Stinson, 1999).

The D-H key agreement is used to make possible the reuse of visual cryptography. The Diffie-Hellman key agreement used an interface known as D-H key interface. This interface is used for password based Encryption. These interfaces typically can be used by the programmer who is implementing a Cryptographic provider or who wants to implement a cryptography algorithm (David Flanagan, 2005). Diffie- Hellman Key agreement is also known as exponential key exchange. This key provides the solution to the key distribution problems, allowing two parties, never having met in advance to share key material for establishing a shared secret by exchanging messages over an open channel. This is a fundamental technique providing unauthenticated key agreement. The main goal of an authenticated Key establishment protocol is to distribute key of data. The established key should have precisely the same attributes as a key established face to face, it should be distributed uniformly at random from the key space, and an unauthorized entity will not be able to learn anything about the key (Alfred J.Menezes, Paul C. Van Oorschot, and Scott A. Vanstone, 1997). D-H key agreement protocols involve the derivation of the shared secret information based on compatible D-H keys between the sender and recipient. The information is then converted into the cryptographic keying material for other algorithms. A variation of the Diffie-Hellman is used for converting the shared secret data into an arbitrary amount of keying materials (Manuel Mogollon, 2008). According to Michael Baake and John A G Roberts (2001, p.1) “Toral Automorphisms will be represented by the uni-modular integer matrices, are investigated with the help of symmetries and also reversing symmetries group of matrices with a simple spectrum through their connection with unit groups in orders of algebraic number fields. The reversibility will derive the necessary conditions in terms of the distinctive polynomial and the polynomial invariants”. This shows that the Voiculescu- Brown entropy of the non-commutative toral automorphism arising from a matrix S in is at least half the value of the topological entropy of the corresponding classical toral automorphism. This is a new method used to prove the position limit laws in the theory of dynamical systems, which is based on the Chen-Stein method combined with the analysis of the homo clinic Laplace operator and some other homo clinic considerations (Massimo Franceschetti and Ronald Meester, 2002, p.2). The main use of this is to generate a disorder in the arrangement of digital images. The equation (1) define the two dimensional matrix.

………………. (1)

The coordinates (x', y') denotes the new position of the two dimensional matrix after randomly selecting its permutation, matrix is denoted as the size of the image, is denotes the secret key of the Toral Automorphism matrix. Let assume that secret image size is pixels, and is 4 (Chao-Wen and Yi-Da Wu, 2008). Then the Toral Automorphisms matrix and the pixels value of the image are given as:

- represent the TA matrix.

The new technology that can be used for the visual cryptography is adaptive order dithering technique. By using this technique the decrypted image size can be reduced and also the quality of decryption image can be improved. In this technique the technique will get adaptive to the data that is used (Nagaraj V. Dharwadkar, B.B. Amberker and Sushil Raj Joshi, 2009). From the above context it can be understood that visual cryptography is a scheme in which the secret data can be transmitted without getting decoded by others.

Chapter 1: Introduction

1.1. Overview

Visual Information system significantly enlarges the applications scope of information systems and typically deals with the general purpose multimedia operating system that is supported by multimedia hardware and high bandwidth network. Visual information system involves variety of facilities for efficient visual information presentation and visualization. This system actually provides inter related visual and multimedia information to support the operations, management and decision making functions in an organization. These are text oriented which provides reports, decision-making information and documents for all levels of hierarchy in the organization. With the increase in multimedia platforms, visual information has become more available (Clement H. C. Leung, 1997). In recent years, there has been a rapid growth of information technology for human to communication on the Internet. Since Internet is public, with the advancement of information technology, communication through internet has increased rapidly. As internet can be accessed by everyone and anyone can easily access the information and transmit it without any protection there is possibility of grabbing the information as it became secondary data. So in order to avoid hacking of sensitive information, it should be encrypted before transmission. In order to protect the information Diffie and Helman (D-H) proposed a key agreement scheme that is implemented when two parties agree on a common session key. This key agreement also helps in improving the reusable process. This method is used to compute a common image for encryption and decryption with two parties (Chao-Wen Chan and Yi-Da Wu, 2008). The D-H algorithm does not encrypt data or make a digital signature. This is exclusively used for the generation of shred secrets. The DH key agreement can be split into three parts; they are parameter generation that generates non secret public value and is expensive process, next is phase1generatres two key exchange values for the parties and phase2 is the originator and recipient that computes the functions in the given image (Blake Dournaee, 2002). DH key agreement has a nice property that it is not sensitive to off-line attacks but it is sensitive to man-in-the-middle attacks (Christian Gehmann, Joakim Persson and Ben Smeets, 2004). In Diffie and Hellman (D-H) key agreement method both the secret and symmetry key are represented in binary image. It is simple and easy to be implemented especially for shadow images. Thus, it can be applied in many electronic business applications. There after Naor and Shamir proposed a methodology named visual secret sharing that provides secrecy to the information and avoids illegal activities; this process is called as Visual Cryptography. This process provides secrecy by partitioning the secret digital image into several shadow images that are recovered by the human visual system by piling all those images together (Jeng-Shyang Pan, Hsiang-Cheh Huang and L. C. Jain, 2004). Hence it can be stated that in order to safeguard the images visual cryptography and DH key agreement are used where the images are split into shadow images and sent which then will be combines and viewed by the human visual system. It is secured by encryption and decryption of images with a key to be presented. Visual cryptography is seen as a one - time pad system that cannot be reused, in further sections of the study the implementation of Diffie and Hellman (D-H) key agreement method is researched in detail so that visual cryptography can be reused.

1.2. Aims and Objectives

Aim:

To research on visual information encryption by D-H Key agreement and visual Cryptography

Objectives:

* Provision of security for hidden images

* Reusing of the technology again and again

* Images should be visible only to human visual system

1.3. Purpose of Study

The main purpose of studying the Visual Encryption is to provide a unified overview of techniques for the encryption of the image and video data, ranging from commercial applications like DVD or DVB to more research oriented topic and recently published material. To serve this purpose of Visual Encryption has the different techniques of a unified viewpoint, it provide an extensive use of Visual Encryption. Digital visual data is usually organized in a rectangular arrays denoted as frames, the elements of these array are denoted as pixels. Each pixel is a numerical value specifies the intensity of the pixels (Andreas Uhl and Andreas Pommer, 2005). In the latest year, there has been a rapid growth of the information technology for the human to communication on the Internet. As Internet has become the open public, anyone can easily read information and perform the successful transmission of the information without protection. In order to provide the proper security to the information, Visual Information Encryption by D-H Key study is necessary (chao-Wen and Yi-Da Wu, 2008). Visual Information Encryption provides the secure connection and protects data from unexpected modification by hackers or other outsiders. In D-H key encryption a common password is required for all the attendees to participate in the same conference, which gives more security to the information (Encryption, 2008). Visual information Encryption provides the Encryption formats as a standard function. Thus, the main purpose of the study is to implement a visual secret sharing scheme through visual cryptography in order to avoid sensitive information being illegally read or modified because the observations made from the recent electronic business applications on the Internet reveal that the amount of data exchanged is small and the exchanged data requires secrecy.

1.4. Research Context

With the rapid increase in visual information, the digital and video encryption approaches are widely studied upon various resources like visual net meetings. This application mostly requires ultra high security to keep the images and video dat confidential among users; nobody can retrieve the content without a key for decryption. Thus, from this point of view image encryption is considered as a basis for visual encryption. Visual Cryptography is a topic that finds its way into every nook and cranny of the networking world. Everyone has their own ideas of how it should work and their own understanding of how it does work. The problem with the encryption is that there are several different types, and these type works in several different ways. And most companies want encryption, they don't necessarily know what type of encryption they want, and what the difference are between the types. Here this is designed to give a good overview of the current encryption technology (Eric Quinn, 2009). The visual cryptography is mainly used in maintaining images secretly for not to be accessed by the unauthorized persons. By using this technology the images can be visual by the user but it cannot be accessed by unauthorized persons. As there is increasing growth in the computer networks and in distributed a computing application visual cryptography plays an important role in providing security (visual cryptography, 2009). In binary images scheme the visual cryptography helps in maintaining the secrecy for not providing authorization to intruders. The visual cryptography provides an infinite computation power that messages cannot be identified. This visual cryptography is in identification of bank customers, verification of electronic voting and anti spam bot measures for maintaining the secrecy to avoid intruder's Visual cryptography provides a way for secretly maintaining the information and data. Visual cryptography is used in many applications for maintaining data secretly for not be authorized by the intruders (Nagaraj V. Dharwadhakar, Amberker and susil Raj Joshi, 2009). This system actually supplies inter related visual and multimedia information to support the operations, management and decision making functions in an organization. This process provides confidentiality by dividing the secret digital image into several images that are healthier by the human visual system by those images together. Visual cryptography strategy is suggested to combine the key agreement scheme with a shadow image without building a secure connection. Thus, visual cryptology uses public key algorithm for having maintain secretly (Kiyoharu Aizawa, Yuichi nakamura and shinichi satoh, 2004). Many organizations are using this methodology for not having interruptions in data. Visual cryptography uses different encryption and decryption techniques and many authentications for not be accessed by unauthorized persons and maintains secrecy. In this research D-H key algorithm is used for having secrecy and privacy can be maintained. By implementation of new encryption schemes provides secrecy in an effective manner.

1.5. Research Method

Qualitative approach is appropriate for this research method. Qualitative Research Practice starts with the premise that one can improve their research skills by seeing what researchers actually do in particular projects and by adding their actions and plans into their own research practice. It actually demonstrates the benefits of using practical methods from real-life knowledge and will be necessary reading for anyone interested in the process of doing social research (Clive Seale, 2004). It is a field of inquisition that explains discipline and subject matters. It is called as ethnographic research. This ethnographic research involves the collection of description data in a natural setting in order to gain insights into phenomenon of interest. This research studies many variables over an extensive period of time to find out the way things are, how and why they came to be that way and what it all means. Qualitative researchers do not want to interfere or control anything. The most common method of data collection involves participant observation (Michael Huberman Matthew and Miles, 2002). Qualitative analysis offers a cluster of very useful procedures like guidelines, techniques etc. It actually refers to the educational issues and the understanding of learning and cognition (Pamela S. Maykut and Richard Morehouse, 1994). Hence, it can be said that the secondary data is preferred for this research while searching the related information to it as the other approaches cannot provide a better data to the research.

Chapter 2: Literature Review

2.1. Overview

Visual Cryptography is a particular encryption method used to hide information in images in such a way that it can be decrypted by the human visual system if the correct key image is applied. This method was suggested by Naor and Shamir in 1994. Visual Cryptography applies two transparent images. One image consist random pixels and the other image consist of the secret information. In visual cryptography it is not possible to recollect the secret information from one of the images. Both transparent images and layers are involved to reveal the information (Kiyoharu Aizawa, yuichi Nakamura and shichi satoh, 2004). The simplest method to implement Visual Cryptography is to bring out the two layers against a transparent sheet. When the random image contains genuinely random pixels then it can be seen as a onetime pad system and will offer infrangibly encryption. In visual cryptography pixel is divided into white and black blocks. In this chapter, importance of visual cryptography is discussed and a New Visual information Encryption Scheme is proposed followed by the explanation of Security analysis on images with the previous technologies.

2.2. Visual Cryptography

Visual Cryptography refers to a secret sharing method that will encrypt the secret message into a number of shares and does not require any computer or calculations for decrypting the secret image rather the secret message will be reconstructed visually by overlaying the encrypted shares the secret image will become clearly visible. Visual cryptography scheme on a set P of n participants can be defined as a method of encoding the secret image into n shares so that the original image will be obtained by stacking specific combination of shares onto each other. Visual cryptography technique was initiated by the Naor and Shamiri at Eurocrypt '94. It is a process used for separating one image into various shares. Visual cryptography solutions functions on binary inputs. Visual cryptography is a special technique used to hide information in images in such a way that it can be decrypted by the human vision when the correct image is used. It uses two images one image contains secret information, in visual cryptography it is not possible to retrieve the secret information from one of the images, both transparent images are required to reveal the information. To print two layers into the transparent sheet is the simplest way to implement Visual cryptography (jeng shying pan, Hsiang cheh Huang and L. C. Jain, 2004). If the random image contains random pixel then it can be seen as a onetime pad system and will offer unbreakable encryption. These two layers slide over each other until they are correctly aligned where the hidden information appears. This type of visual cryptography which restores the image by stacking some significant images together is known as extended visual cryptography. Generally, visual cryptography suffers from the deterioration of image quality. The basic two cryptography models consists of a secret message encoded into two transparencies', one transparency representing the cipher text and the other acting as a secret key. Both transparencies appear to random dots when inspected individually and does not provide any information about the original clear text. By carefully aligning the transparencies the original message is reproduced (Borivoje Furht, Edin Muharemagic and Daniel socek, 2005). The original decoding is accomplished by the human visual system. Visual cryptography scheme is a visual secret sharing problem in which the secret message is viewed only in black and white pixels. Each pixel in the original image is represented by at least one sub pixel in each of the n transparencies or shares generated. Each share is comprised of collection of m black and white sub pixels where each collection represents a particular original pixel. The contrast of Visual Cryptography Scheme is the difference between the minimum number of black sub pixels in a reconstructed (secret) black pixel and the maximum number of black sub pixels in a reconstructed (secret) white pixel (Kiyoharu Aizawa, Yuchi Nakamura and Shinichi Satoh, 2004). The main instantiation of visual cryptographic realizes a cryptographic protocol called secret sharing. The important thing in secret sharing is it relies on a human visual system to perform the decryption. In a conventional secret sharing a secret shared among n participants can pull their shares and recover the secret but the subsets of the forbidden can obtain no information about that. Visual secret sharing schemes inherits all applications of conventional secret sharing schemes most notably access control.

An example of the encoding of white and black pixels in a 2 out of 2 scheme can be seen in 1. Here two shares out of the two generated would be needed to recover the original image. Since only two shares are generated, n = 2. White box represents a single white or black pixel in the original image. Sub pixel assignments that would be given to shares #1 and #2 respectively. The number of sub pixels per share used to represent the original pixel is four Finally, the overall visual effect when shares #1 and #2 are correctly aligned on top of one another. Notice that when the shares in this example are combined the original black pixel is viewed as black; however, the original white pixel takes on a grey scale. The structure obtained from either white or black pixel representation can be described by an n. Similar to the area of the secret sharing, more generally structures have been studied in the visual cryptography. The basic model of the visual cryptography consists of a several umber of transparency sheets. On each transparency a cipher text is printed which is identical from random noise. The hidden message is reconstructed by stacking a certain number of the transparencies and viewing them. The system can be used by anyone without any knowledge of cryptography and without performing any cryptographic computations. Naor and Shamir have developed the Visual Secret Sharing Scheme (VSSS) to implement this model [Naor95] (Mizuho Nakajima and Yasushi Yamaguchi, 2002). Thus, from the above discursion it can be stated that Visual cryptography is a special technique used to hide information in images in such a way that it can be decrypted by the human vision when the correct image is used. It is a simple and clear scheme that can partition the secret image into a number of shadow images and the dealers can distribute these shadow images to participants. The Visual cryptography scheme makes use of human visual system for recovering secret images by staking various shadow images.

2.3. Importance of Visual Cryptography

Visual Information system importantly elaborates the diligences scope of information systems and deals with the multimedia operating system which is supported by multimedia hardware and high bandwidth network. These are text oriented which provides reports, decision-making information and documents for all levels of hierarchy in the organization (Carlo Blundo and Stelvio, 2005). With the increase in multimedia platforms, visual information has become more available with the advancement of information technology; contact through internet has increased rapidly. Visual information system requires many kinds of facilities for effective visual information presentation and visualization. This system actually supplies inter related visual and multimedia information to support the operations, management and decision making functions in an organization. As internet can be accessed by everyone and anyone can easily access the information and transmit it without any protection there is possibility of grabbing the information as it became secondary data. So in order to avoid hacking of sensitive information, it should be encrypted before transmission (Yongfei Han, 1997). In order to protect the information Diffie and Helman (D-H) proposed a key agreement scheme that is implemented when two parties agree on a common session key. This key agreement also helps in improving the reusable process. This technique is utilized to calculate a common image for encryption and decryption with two parties. The D-H algorithm does not encrypt data or make a digital signature. This is exclusively used for the generation of shred secrets. The DH key agreement can be split into three parts; they are parameter generation that generates non secret public value and is expensive process, next is phase1generatres two key exchange values for the parties and phase2 is the originator and recipient that computes the functions in the given image. DH key agreement has a nice property that it is not sensitive to off-line attacks but it is sensitive to man-in-the-middle attacks. There after Naor and Shamir proposed a methodology named visual secret sharing that provides secrecy to the information and avoids illegal activities (Jeng-Shyang Pan, Hsiang-Cheh Huang and L. C. Jain, 2004). This process is called as Visual Cryptography. This process provides secrecy by partitioning the secret digital image into several shadow images that are recovered by the human visual system by piling all those images together. It is secured technique where the data cannot be traced by others. In classic secret sharing, algorithms for splitting and sharing secret information are a stem of cryptography. In the most general case, their objective is to generate such parts for the data and that could be shared by multiple authorized persons. This problem of splitting information in a manner allowing its reconstruction by a certain n-person group interested in the reconstruction of the split information. Algorithm solutions developed to achieve this objective and at the same time none of the groups of participants in such a protocol, whose number is lesser than the required m persons. It leads to opposing to read the split message. The algorithms for dividing information make it possible to split it into chunks known as shadows that are later distributed among the participants of the protocol. So that the shares of certain subsets of users collective together and these are capable of reconstructing the original information. There are two groups of algorithms for dividing information, namely, secret splitting and secret sharing. In the first technique, information is distributed among the participants of the protocol, and all the participants are required to put together their parts to have it reconstructed. A more universal method of splitting information is the latter method, i.e. secret sharing (Marek R. Ogiela and Urszula Ogiela, 2009). Thus, from the above discursion it can be stated that visual cryptography plays a vital role in securing the data and also in sharing the secret message as the data transferred through internet has been increased. rapidly.

Advantages of visual cryptography

1. Visual cryptography is simple to be implemented.

2. Encryption incase of visual cryptography does not require any hard problem dependency.

3. Specifically decryption algorithms are not required because a person aware of cryptography can easily decrypt the message.

4. Cipher text can be Fax or e-mail in case of visual cryptography

2.4. Security analysis on images with the previous technologies

The security analysis is the major aspect of the encryption. Analysis to the field of security will encounter the serious obstacle that deal is by nature not an exact science. The previous technologies which where there before the D-H key agreement encryption are manual encryption, transparent encryption, symmetric encryption and asymmetric encryption (Fedora Documentation Project, 2009). Visual cryptography can be seen as a one-time pad system. Then, it cannot be reused. Diffie and Hellman (D-H) key agreement method and Toral Automorphism (TA) such that visual cryptography can be reused. Both secret and symmetry-key are represented in binary image. The proposed scheme is simple and easy to be implemented for shadow images. Therefore, it can be used in many electronic business applications (Chao-Wen Chan and Yi-Da Wu, 2008). The Manual Encryption is a technique that will involve the use of encryption software. In this computer programs are used for encrypt various bits of information digitally. In this technique the encryption key is provided later in the process. The main security issues are the potential leakage through security insensible program and also the bad implementation may lead to re-encrypt with same key for same password (Bruice Schneier, 2007). Transparent Encryption is another type of computer software encryption. In this technique the data can be downloaded onto a computer to encrypt automatically. Every executable application and file created in the computer has an encrypted copy that can withstand power surges and protects information in case a computer is stolen. The security issues is the data which is automatically encrypted can be taken if the key provided is known (Cetin K. Koc, David Naccache and Christof Paar, 2001). The Symmetric Encryption is in which a letter or number coincides with another letter or number in the encryption code. This technique is commonly referred to as secret-key encryption. In this only single key is used for encrypting and decryption. In a situation where large numbers of people want to communicate securely, like modern internet commerce it is impossible for everyone to share a secret key. So the security of the data will not be possible in this type of technique (Ivan Ristic, 2005). The Asymmetric Encryption is a technique which is generally done electronically. This is also called as public key encryption. This will involves pairs of keys: a public key which can be made openly available, and a private key. Once information has been encrypted with the public key, nobody but the holder of the private key can decrypt it. In reverse, if the private key is used for encryption, anyone with the public key can decrypt it. Asymmetric encryption has a property that figuring out the key from the other should be as hard as decrypting the message without the key. Asymmetric encryption is slower than symmetric encryption, even on fast computers, so most modern encryption uses a combination of both methods (Eric Cole, Ronald Krutz, 2005). When compared with the asymmetric encryption D-H key agreement is the technique which is more advantages is security issues. Hence from the above context it can be understood that the manual encryption, transparent encryption, symmetric encryption and asymmetric encryption are the technique which are many security issues, so the advantage technique in this is D-H key agreement encryption. This technique has the les security problems when compared with the other techniques. Hence from the above discussion it can be understood that security analysis is the important aspect in encryption process. D-H key agreement is the fundamental technology in image encryption process. The main security problems are the potential leakage during security insensible program and the bad implementation may lead to re-encrypt with same key for same password. So many techniques are used to encrypt the image. Transparent Encryption is most important type of computer software encryption. In this technique the data can be downloaded onto a computer to encrypt automatically. D-H key agreement is the best technique; it provides more advantages are security issues.

The overlapping of image in the space is the basic operation of visual secret sharing scheme. The effect of persistence of vision in human vision system will bring the stacking while fast showing two images in order. The human vision property is utilized by proposed in video secret sharing scheme. A sequence of frames are expected after the video secret sharing process, that reveal nothing individually but display a secret while playing successive frames speedily. By knowing the frames an eyedropper can't get information that is discontinuous.fi is a processed from ith frame, the frame which is reconstructed from the ith is frei (fi is analogous to shares in VSS.)

For implementing the concept, a VSS is applied for for each frame in original video sequence, such that fi + fi+1 = frei.

The secret will be reconstructed by the required scheme which is shown in the experimental results and will also the pixels are randomly distributed so that they reveal nothing about the original secret. This scheme also has some weakness. First, video file size is quite large after this process. The worse, thing is compression don't work since the random distribution nature of pixels in these frames (Horst Reichel and Sophie Tison, 2000). Second, a small amount of information leakage occurs due to the dependency between fi and fi+2.

2.5. Proposing a New Visual information Encryption Scheme

Visual encryption schemes can described as determistic and probabilistic. The determistic schemes are public keys where the plain same text will always encrypted to the same cipher text the problem is obtaining with the subset of message space. In encryption schemes consists of pair of decryption which is applied by the sender in order to send the message and the sender attach the algorithm to the message and sends the result called chipper text (Oded Goldreich, 2007). To the received cipher text the receiver applies the decryption algorithm to it and sends the original message. It is provided with secret communication where it can receive communication by the wire tapping otherwise the wire tapper can decrypt the cipher text exactly done by the receiver. Here, two schemes such as D-H key agreement and toral automosrphism are proposed. This arrangement was developed by Whitfield Diffie and Martin Hellman. The D-H keying is an algorithm which has a number of secret connectivity protocols. This means of securely transmitting a secret to be which can be shared between two parties. The transmission is done un-trusted network in real time. A shared secret is critical for two parties who likely have not communicated before; it is used so that they will be able to encrypt communications. D-H is used by protocols such as Internet Protocol Security (IPSec), Secure Shell (SSH), and Secure Sockets Layer (SSL) (Carts, D., 2001). In D-H key agreement it is problem with symmetric encryption is it is much difficult to share the encryption key with symmetric encryption (David Flanagan, 2005). If the user1 want to send the secret message to user2 then both the users should contain same encryption key. Toral automorphism represents unimodular integer matrices which are investigated with reference to the symmetric and reversing symmetric. Symmetric group metrics form through their connection with unit groups in order to algebraic number field. Reversing symmetric within affine transformation metrics are the general settings of integer matrices beyond the unimodular ones. Toral automorphisms as chaotic 2-D integer vector generators which is used for manipulate digital image watermarking. This is an embedding algorithm that can be used for providing the robustness under the condition when the filtering and compression is required.

We propose also an embedding algorithm which provides robustness under filtering and compression

Another proposed solution for visual information system is a new scheme for visual cryptography which will use DHCOD technique to embed the generated shares into some cover image. It has several phases those are listed below (Oded Goldreich, 2007):

Visual Cryptographic Encryption

In this very first phase, the researcher will do visual cryptography encryption. It consists generation of shares using any basic visual cryptography model. Encryption is done by scrambling the visual data into a form in which the data cannot be recognizable and meaningless variants. Visual cryptographic solutions operate on binary inputs (Oded Goldreich, 2007). Therefore, natural (continuous-tone) images must be first converted into halftone images by using the density of the net dots to simulate the original gray or color levels in the target binary representation.

Generation of Watermarked Shares using

DHCOD: This is the three phase of our approach which will embed shares generated from the first phase into some cover images. DHCOD technique is used to hide a binary visual pattern in which the two or more ordered dither halftone images are used. These are the images which can be taken from the same or different multi-tine images. In this scheme shall generate the shares using basic visual cryptography model and then embed them into a cover image using a DHCOD technique, so that the shares will be more secure and meaningful (Debasish Jena and Sanjay Kumar Jena, 2009). For watermarking we will use DHCOD algorithm discussed under section 3.

Visual Cryptographic Decryption: This is the last phase of proposed scheme. In this phase we will do visual cryptographic decryption. In this scheme the information can be reconstructed with the human visual system directly. The devices need not be used for the decryption of the information. So the design of decryption will become to easy (Oded Goldreich, 2007). Visual cryptographic decryption does not need any type of decryption algorithm or computation.

2.6. D-H key Agreement

The DH key interface represents Diffie-Hellman public/private key pair used in the Diffie-Hellman key- agreement protocol. This interface is for password based Encryption. These interface are typically has interest only in programmer who are implementing a Cryptographic provider or who want to implement cryptography algorithm (David Flanagan, 2005). Diffie- Hellman Key agreement is also called as Exponential key exchange. This is a fundamental technique providing unauthenticated key agreement. This key provide the first practical solution to the key distribution problems, allowing two parties, never having meet in advance or shared key material to establish a shared secret by exchanging messages over an open channel. The security rests on the intractability of the Diffie-Hellman problem and related problem of computing discrete logarithms provides protection of the resulting key from passive adversaries (Alfred J.Menezes, Paul C. Van Oorschot, and Scott A. Vanstone, 1997). The main goal of authenticated Key establishment protocol is to distribute keying data. Ideally, the established key should have precisely the same attributes as a key established face to face, it should be distributed uniformly at random from the key space, and unauthorized entity should learn anything about the key. The key agreement protocols which provide the service of the implicit key authentication or explicit key authentication are provided only on one rather than other Encryption application (Stafford Tavares and Henk Meijer, 1999). The main key agreement features are the pairing procedure and updates of link keys. The pairing principle with manual assisted key agreement is the most suitable for the hoc creation of security associations. Even if the existing pairing principle is nice for the hoc creation of the secure connections, it gives no flexibility n terms of the key agreement. It might very well be the case that the user would like to avoid the pairing procedure and instead use precond security association based on the secret or public keys (Christan Gehrmann, Joakim Persson and Ben Smeets, 2004). The agreement method elements appear as the content of the key information element because, like key information, it yields a key. This key information is in turn, of a child of an Encrypted data, encrypted key, or Signature element. The key agreement protocols base their security on the computational complexity of an underlying mathematical problem. One such problem is the discrete logarithm problem, which is on the basis of the several key agreement protocols in the literature (Yang Xiao, 2007). The most common problem with group key management schemes is during the process of rekeying, all member stop the data communication until the new group key is distributed called block. The basic idea about the Diffie-Hellman key agreement is there are two types of keys: front end keys and back end keys. The front end keys are computed by all group members where as in back end keys, each member have had their own keys. So that no one can compute the data without their presence (Xukai Zou, Byrav Ramamurthy and Spyros Simos Magliveras, 2005). DH key aggrement protocols involves in the derivation of the shared secret information based on compatible DH keys from the sender and recipient. The variation of the Diffie-Hellman is used for converting the shared secret data into an arbitrary amount of keying materials (Manuel Mogollon, 2008). The DH key agreement protocol can be extended to a multi parity key agreement using tree based structure. This requires several rounds of interaction among the involved parties. It is very interesting key agreement protocol. In this protocol, any number of parties can agree a common secret key in just two rounds. This DH key protocol is insecure against the adversary because of a man in the middle of the attacks (Nicolas Sklavos and Xinmiao Zhang, 2007). In this attack the adversary establishment separates the common key with Alice and Bob, or vice versa. The key agreement protocol removes the problem by using some kind of authentication measures.

2.7. Toral Automorphism

Toral Automorphisms, represented by the unimodular integer matrices, are investigated with respect to their symmetries and reversing symmetries group of matrices with a simple spectrum through their connection with unit groups in orders of algebraic number fields. For the question of reversibility, this derives the necessary conditions in terms of the distinctive polynomial and the polynomial invariants. This shows that the Voiculescu- Brown entropy of the non-commutative toral automorphism arising from a matrix S in is at least half the value of the topological entropy of the corresponding classical toral automorphism. This is a new method used to prove the position limit laws in the theory of dynamical systems, which is based on the Chen-Stien method combined with the analysis of the homoclinic laplace operator and some other homoclinic considerations ( Manfred Denker, Mikhail and Anastasya sharova, 2002). This is a two dimensional matrix which permutes a set of coordinates. The main use of this is to generate a disorder in the arrangement of digital images. The equation (1) define the two dimensional matrix.

………………. (1)

The coordinates (x', y') denotes the new position of the two dimensional matrix after randomly selecting its permutation, matrix is denoted as the size of the image, is denotes the secret key of the Toral Automorphism matrix (Chao-Wen and Yi-Da Wu, 2008). Let assume that secret image size is pixels, and is 4. Then the Toral Automorphisms matrix and the pixels value of the image are given as:

- represent the TA matrix.

- represent the pixels value of image before using the TA matrix.

- represent the Pixels value of image after using TA matrix.

The pixels value of the image is at the location before using the TA. After using TA the location moves to location. The prefix- suffix automation induce the natural partition of the fundamental domain such that the action of toral automorphism associated with the incidence of the matrix the substitution is coded, with respect of the partition, by set of the prefix-suffix automation (Pytheas Fogg, N. and Valerie Berthe, 2002). The main use of the toral automorphisms is as chaotic 2-D integer vector generators in order to manipulate digital image watermarking. It can also be propose for embedding algorithm which provides robustness under filtering and compression. Hence this is a two dimensional matrix which is more preferable for finding the position limits in the pixels images. This also focus it view on the geometric construction of Rauzy fractals that gives the Markov partitions and the related substitution tilling.

2.8. Summary

Visual cryptography strategy is suggested to combine the key agreement scheme with a shadow image without building a secure connection. It is permanent solution for the image encryption to secure it. Visual cryptography is a cryptographic technique that allows visual information to be encrypted in such a way that the decryption can be performed by the human visual system, without the aid of computers. When compared with other threshold schemes, visual cryptography is used to protect secrecy and can also be used to ensure that a given subset of principals can neither retrieve the secret nor they can prevent the principals from retrieving the secret. Visual cryptography is applied for encrypting the things like handwritten notes, graphic images, and pictures as well as typed text stored as a graphic image. The encryption procedure encrypts a secret image among the shares in secret sharing concept which are so called noise like secure images which can be transmitted or distributed through an illegal communication channel. By making use of properties present in the human visual system it can be forced to know the recognition of a secret message from the shares which are overlapping and the secret image is decrypted without using any additional computations and without any knowledge of cryptography. The schemes that are used is Daffier and Hellman key agreement and total auto Orphism such that it can be reused. Hence, the given and proposed scheme is flexible, which can be implemented easily and is much secure for shadow images.

Chapter 3: Research Methodology

Visual Cryptography is a type of cryptography which encodes a number of images in the way that when the images on transparencies are stacked together, the hidden message appears without a trace of original images. The decryption is done directly by the human visual system with no special cryptographic calculations. There are varieties of techniques used for this encryption process (Chemnitz, 2003). Visual cryptographic technique is applied to provide privacy protection while transmitting sensitive data between offices and this technique will also make it quiet difficult for the recipient to modify the source thereby providing authenticity for the source.

The one of the main process proposed in this topic for encrypting the image to retrieve the data is D-H Keys agreement. The notations used for encrypting the image in this proposed scheme for the D-H Keys are given below:

Denotes the large prime integer such as discrete logarithm problem in is hard.

It is public primitive integer in Modular, where g is not equal to 1.

It is a secret integer appearing in the shadow image chosen by both sandy and Zen.

This denotes a secret integer randomly selected by sandy.

This denotes a secret integer randomly selected by Zen.

Denotes a common image selected by the two parties, and denotes the pixels value of the image at location.

This denotes the two dimensional Toral Aotomorphism (TA) matrix, where is equals to.

This denotes the image permutated times by TA, where k is the secret key for the TA matrix.

This equation denotes an image permutation function derived from n and, and it its permuted coordinates of the image n time with the TA algorithm. Where

“ “

and

For all

This scheme consist of the three phase for encrypting the image which is sent to Zen by Sandy. The four phases are:

* Initialization Phase

* Session key generation phase.

* Encryption phase.

* Decryption Phase

Initialization phase

This is the first phase in the proposed scheme for the image encryption. Sandy and Zen agree with the common image of having the property of two dimensions that is and a secret integer k, where I include block. In that each block consist of pixels arranged in a random way, then the pixels in the corresponding two blocks are black and other two blocks are white.

This hides the image in the black and white blocks correspondingly (Debasish Jena and Sanjay Kumar Jena, 2006). The black block represents the zeros and white blocks represent ones. Phase initialization is a 6-tuple scheme; it assumes that each pixel appears as n version called shares one for each transparency.

Session Key Generation Phase

This phase is base on the D-H key agreement scheme. Diffie-Hellman key agreement solves the problem of establishing a shared secret key among multiple parties who have no prior knowledge of each other. It is the first public key distribution protocol that gave a new direction to the cryptography. It is an important key distribution protocol, two entities Sandy and Zen after having agreed to primary number N and g is the primitive group, can generate a secret session key (Ioannis G. Askoxylakis, Damien Sauveron and Konstantinos Markantonakis, 2006). Following are the steps involve in the generating a session key.

* Sandy selects a random integer calculates and Sandy sends sandy, to Zen. The entity of sandy's image is sent to Zen.

* Zen selects a random integer and calculates Zen uses the shared image I to decrypt and calculates

* The session key is derived from this value by selecting a certain number of bits. Finally, a random image is challenged, is generated. Then Zen transmits:

* Sandy uses image I to decrypt from this quantity the value of K is calculated. K is in turn used to decrypt. Sandy then generates a random image.. Sandy sends).

* Zen decrypts, and verifies that is correct. Zen sends

* Sandy decrypts the image to obtain the. And verifies that it matches the original Image.

After performing all the steps mentioned above, Sandy and Zen can obtain a common session key or that is Now sandy and Zen keep this common session key K for the image encryption and decryption.

Encryption Phase

This encryption phase is based on the Visual Cryptography. The image which is to be send as a secret image a (2, 2) threshold visual cryptographic image can be partitioned into two shadow images. If only one shadow image is selected randomly then the other image can be determined uniquely (Bruice Schneier, 2007). In this proposed scheme if sandy wants to send the secret image as image A to Zen. Then Sandy computes a common shadow image as:

The common shadow image that is is computed by computer. According to the threshold value (2, 2) visual cryptography, then the other image that is can be computed by image and common shadow image that is as the formula shown below:

This gives the result such as and equals or. The can be deduced from. By using this process the shadow can also be computed by computer. Then Sandy sends the to Zen.

Decryption Phase

When the encrypted shadow comes to Zen, then this secret image can be recovered by the Zen by stacking, where Alfred J.Menezes, Paul C. Van Oorschot, and Scott A. Vanstone, 1997). The formula given below shows the decryption phase.

That is image =.

So, in order to achieve both properties of the encryption and decryption in this study it has been propose to use adaptive order dally technique during half toning and then apply existing Visual Cryptography Scheme for binary image to accomplish the creation of shadow image. It should be noted that although the use of binary phase masks for the key and the encrypted information. The encryption technique which is presented in this study could equally well be applied to systems in which multiple phase levels are used for the masks and keys. However, the fabrication issues involved in the production of a multiple phase level fixed phase mask are more complicated than for the production of a binary mask, so for the purposes of the experimental demonstration of decryption binary input and output phase masks and phase keys have been used for decrypted the original image.

Chapter 4: Results

MATLAB (MATrix LABratory) is an interactive software system for computing numerical and graphic functions. From the name itself it shows that, MATLAB is especially designed for matrix computations for solving the problems in linear equations, computing Eigen values and Eigen vectors, factoring matrices, and so forth. A variety of graphical capabilities and extension through program written in its programming language are the additional features present in it. Many such programs come in evaluating the system, a number of these extend MATLAB'S capabilities to nonlinear problems, such as the solution of initial value problems for ordinary differential equations (Richard Johnson, 2002) MATLAB is designed to solve problems numerically, that is, in finite-precision arithmetic. Therefore it produces approximate rather than exact solutions, and should not be confused with a symbolic computation system (SCS) such as Mathematical or Maple. It should be understood that this does not make MATLAB better or worse than the Symbolic Computation Systems; MATLAB is a tool designed for different tasks and is therefore not directly comparable with any other computational programs. In the following sections, it gives an introduction to some of the most useful features of MALAB (David Hiebeler, 2009). MATLAB includes plenty of examples to learn and use the MATLAB in the best way, while running MALAB. MATLAB can be benefited by, Engineering personnel responsible for studies of electric power systems, control systems, and power electronics circuits will benefit from this course. This course will be also useful for engineers, researchers and educators involved in research and development for electrical engineering applications.

In this project MATLAB software has been used for implementing programs because of its versatile advantages when compare to other software tools. In MATLAB it has already inbuilt image processing tools so it can be easy to run the program. This has a simple programming environment including control structures like loops and selections. It can solve the linear algebraic system for vectors, matrices and functionality like computing products and inverses, scaling, summing, multiplications, factorizations, and so on, as in this project matrix and logical operation are used so MATLAB is preferred. It has the simple property of graphic interface for visualization and simulation Open component system based on toolboxes which can be created, modified, customized and shared by the users.

This Visual Information encryption has the original image which sandy has to be sent to Zen. This is the secret image that is to be embedded with the shadow image. The D-H Keys is used to generate the shadow image for this original image. This is developed in the Initialization Phase of the Cryptography. Initially the image which is to send in the secret form is chosen and then it is converted in the binary form with the help of two dimensional matrixes. Now the original image is ready to embed with the covered image that is common image. Hence it can be stated that the original image used for the security which is to be sent from Sandy to Zen.

As the common image shown below in the 2 is a two dimensional image used to cover the original image. This image is having the property of the, it is formed by black and white blocks, the black block is least significant bit and white blocks are most significant bit. The pixels are divided n the format of the n version shares. This image is developed by the session key generation phase. This phase uses the Diffie-Hellman key agreement to generate the secret two shadow image. The common image is nothing but it is a shadow image of the original image in the same two dimensional matrix forms. So that it is easy to embed the two images for the security. Hence this states that the common image is used for hiding the original image in the form of two dimensional image.

After hiding the original image with the help of the common shadow image then the image which is obtained is the secret image. There are two secret integers selected by the two parties Sandy and Zen. The two secret integers are selected by Sandy and Zen. With the help of the secret key generation this image is generated as. This is the secret image which is send by the sandy to Zen. This equation shows the image permuted function. The secret image is shown in the 3. From the above context it can be understood that the two image are combined for forming the secret image.

Reconstructed binary image is shown in the 4. This binary image is developed in the Encryption phase. In this reconstructed binary image, if the image is selected randomly then the other image can be determined uniquely. By using some binary function to the image. The common image is computed with the help of computer. In this image the common image and binary image are seen partially. The encrypted image means removing of the shadow image from the original image, so that the encrypted image is not viewed clearly. To view this image clearly, this image should be decrypted. From the above context it can be understood that that reconstructed binary image is the image same as the watermarking format.

To add color to the image decryption phase must be used in this stage. The image is decrypted by using the XOR operation at the decryption phase. At this stage the image can be viewed very clearly. This is the secret image obtained at the final stage of decryption. Although it is known fact that MATLAB is generally reliable, but crashes are possible when using third party MEX functions or extremely memory intensive operations, for example, with video and very large arrays. This can handle the two parties very easily. So while running the program must take care of the coding implemented.

Effectiveness of Proposed scheme

The effectiveness of this visual information encryption is proposed in a very efficient way this has many advantages such as:

Recording of the processing image is easy - By using the MATLAB in this proposed scheme it has a very simple general purpose programming language. When it is used to process images one generally writes function files, or script files to perform the operations. These image files form a formal record of the processing used and ensures that the final results can be tested and replicated by others in very easy way.

Access to implementation details - With the help of MATLAB this scheme provides many functions for image processing and other tasks. Most of these functions are written in the MATLAB language and are publicly readable as plain text files. Thus the implementation details of these functions are accessible and open to inspection. The defense can examine the processing used in complete detail, and any challenges raised can be responded to the image in an informed way by the prosecution. This makes the Visual information encryption very different from other image security applications, such as watermarking. It should be noted that some visual information functions cannot be viewed. These are generally lower level functions that are computationally expensive and are hence provided as code functions running as native code. These functions are heavily used and tested and can be trusted on this proposed scheme with considerable confidence.

Numerical Accuracy - In general, the image files store data to 8 bit precision. This corresponds to a range of integer values from 0-255 that is 256 bits. A pixel in a color image may be represented by three 8 bit numbers, each representing the red, green and blue components as an integer value between 0 and 255. Typically this is liberal precision for representing normal images. However as soon as one reads this image data into memory and starts to process it is very easy to generate values that lie outside the range 0-255. For example, to double the contrast of an image one multiplies the intensity values by 2. An image value of 200 will become 400 and numerical overflow will result. How this is dealt with will vary between image processing programs. Some may shorten the results to an integer in the range 0-255; others may perform the mathematical operations in floating point arithmetic and then rescale the final results to an integer in the range 0-255.

It is here that numerical precision, and hence image fidelity, may be lost. Some image processing algorithms result in some pixel values with very large magnitudes that is positive or negative. Typically these large values occur at points in the image where intensity discontinuities occur, the edges of the image are common sources of this problem. When this image with widely varying values is rescaled to integers in the range 0-255 much of this range may be used just to represent the few pixels with the large values. The bulk of the image data may then have to be represented within a small range of integer values, say from 0-50. Clearly this represents a considerable loss of image information. If another process is then applied to this image the problems can then accumulate. Trying to establish the extent of this problem, if any, is hard if one is using proprietary software. Being a general programming language it is possible to have complete control of the precision with which one represents data in MATLAB. An image can be read into memory and the data cast into double precision floating point values. All image processing steps can then be performed in double precision floating point arithmetic, and at no intermediate stage does one need to rescale the results to integers in the range 0-255. Only at the final point when the image is to be displayed and/or written to file does it need to be rescaled. Here one can use histogram truncation to eliminate extreme pixel values so that the bulk of the image data is properly represented. Only prime numbers are used to develop the secret key algorithm. A random 10digit number is used as standard recommendations. A limitation was placed on the size of the prime number, in order to prevent the algorithm in taking several universe lifetimes in finding out the magnitude. The security will get reduced by implementing this. This reduction in number of prime number can be used for chat applications. The limitation which is specified above that is secret value calculated by both parties at the end of the algorithm was not an adequate key length. So the image taken is treating the value as a secret image and using it to derive the encryption key. Since both parties have the same secret value they will derive the same encryption key. This is a new visual cryptography scheme which combines the key agreement scheme with a shadow image without building a secure connection. Even if many eavesdroppers listen over the public communication channel, we can immediately transmit a secret message to others. The possible solution to this encryption is to use the visual data in the form of progressive, scalable, or embedded bit streams. In such bit streams the data is already organized in layers according to its visual importance due to the compression procedure and the bit streams do not have to be parsed to identify the parts that should be protected by the encryption process. In previous work, several suggestions have been made to exploit the base and enhancement layer structure of the scalable profiles as well as to use embedded bit streams and to construct efficient selective encryption schemes. Among various advantages of Visual Cryptography Schemes is the property that Visual Cryptography Scheme decoding relies purely on human visual system, which leads to a lot of interesting applications in private and public sectors of the society. Visual Cryptography is used with image, therefore giving the crypto analyst little to work with. As with any analysis techniques, having little cipher text inhibits the effectiveness of a technique being used to break an encryption. Hence the Visual Cryptography uses short image, public keys can be encrypted using this method. Visual Cryptography has proved that security can be attained with even simple encryption schemes.

In any key agreement protocol secrecy is an important security property and when compared to other protocols a new authenticated Diffie-Hellman key agreement protocol with half forward secrecy is proposed. It is based upon a single cryptographic assumption and it is user authentication and shared key authentication. This method efficiently provides forward secrecy when compared to other parties, it also reduces the damages resulted from the disclosure of the user's secret key and it is very beneficial for today's communication with portable devices. Die-Hellman key exchange protocol with the digital signature algorithm (DSA) is used to achieve mutual authentication of the established key. One of the parties may choose to reuse public keys in Die-Hellman key agreement protocol for reducing the computational workload and to mitigate against denial of service attacks. Key agreement is basically an essential in secure communication for establishing session keys. The proposed Die-Hellman key agreement protocol is effective based on a single cryptographic assumption and being user authentication as well as shared key authentication.

Chapter 5: Discussion

The scope of applications is very high for visual information systems and will deal with applications which are related to multimedia hardware and bandwidth. The availability of the visual information will be high as the number of multimedia platforms. The secret information can be hacked in the internet because it is been used by many of the people. This can be avoided by encrypting the data before the transmission is being done. The technologies that were used before the D-H key agreement are all manual encryption, transparent encryption, symmetric encryption and asymmetric encryption. Symmetric Encryption is in which a letter or number coincides with another letter or number in the encrypted form. This technique is commonly referred to as secret-key encryption. The Asymmetric Encryption is a technique which is generally done electronically. This is also called as public key encryption. Diffie and Helman key agreement is widely used because it is the advanced version and has no drawbacks in this process. This also enables to reuse the information again and again. When compared with the asymmetric encryption D-H key agreement is the technique which is more advantages is security issues. This technique has the less security problems when compared with the other techniques. The main goal of authenticated Key establishment protocol is to distribute keying data. Ideally, the established key should have precisely the same attributes as a key established face to face, it should be distributed uniformly at random from the key space, and unauthorized entity should learn anything about the key. Encryption and digital signatures are used in this process. It has an advantage that it is not sensitive to off-line attacks. This is sensitive only to manmade attacks. Visual secret sharing came into existence with the advancements of technologies. Visual secret sharing provides secrecy to the information and is completely out of illegal activities. This process is called as Visual Cryptography. This provides secrecy by portioning the secret digital images into several shadow images that recovered by human visual systems. All these are achieved by using MATLAB software which is a high level language with many tool boxes. All numerical and graphical computations are covered using this software. This helps by encrypting the secret image in the shadow images. This makes use of D-H key agreement. The Manual Encryption is a technique that will involve the use of encryption software. In this computer programs are used for encrypt various bits of information digitally. In this technique the encryption key is provided later in the process. The DH key agreement protocol can be extended to a multi parity key agreement using tree based structure. This requires several rounds of interaction among the involved parties. It is very interesting key agreement protocol. In this protocol, any number of parties can agree a common secret key in just two rounds.

With the growth of information technology, communication through internet has increased. With the increase of this usage the communication and transmission of data has increased, but without security. To provide security, visual information with D-H key is necessary. This protects the data from unexpected modifications from hackers. This process involves password to be entered by all the attendees to get participated in the conference which adds security to the data. Qualitative approach is used to analyze this project. With this approach one can improve their research skills. This helps in using practical methods from real life knowledge. Qualitative researchers do not want to interfere or control anything. The most common method of data collection involves participant observation. The main purpose of this project is to hide the information in the images by encryption. This hidden image can be viewed by the human visual system only by decryption. In this process the two layers are brought against a transparent sheet and the image is divided into black and white blocks. The black block represents the zeros and white blocks represent ones. Two images are produced and one image is not sufficient to retrieve the secret information and both the transparent images are required to retrieve the secret information. These two images should be placed over one another and should slide over the other till it is correctly aligned and the secret image appears. This process is called as extended visual cryptography. This is a visual secret sharing problem in which the secret image is viewed only in black and white pixels. Here each pixel in the original image is represented by at least one sub pixel in each of the n transparencies or shares generated. The basic model of visual cryptography consists of several number of transparency sheets. Each transparency sheets consists of cipher text which is identical from random noise which is reconstructed by stacking a certain number of the transparencies and viewing them. The algorithms for dividing information make it possible to split it into chunks known as shadows that are later distributed among the participants of the protocol. So that the shares of certain subsets of users collective together and these are capable of reconstructing the original information. The algorithms are of two groups namely secret splitting and secret sharing where in first case the information is distributed among the participants of the protocol and all the participants who have to put them together to reconstruct it. The key agreement protocols base their security on the computational complexity of an underlying mathematical problem. One such problem is the discrete logarithm problem, which is on the basis of the several key agreement protocols in the literature. In order to achieve both properties of the encryption and decryption in this study it has been propose to use adaptive order dally technique during half toning and then apply existing Visual Cryptography Scheme for binary image to accomplish the creation of shadow image.

Chapter 6: Conclusion and Recommendations

6.1. Conclusion

Visual cryptography raised the scope of the information system where it can be handled with the usual multimedia operating system which is supported by the bandwidth and hardware network. Visual cryptography system requires the mixture of conveniences for efficient visual information presentation and visualization. This method basically provides interrelated visual and multimedia information for supporting the operations, management and decision making functions in the organization. These are content oriented which provide reports and documents for the all the levels of the hierarchy in the organization. Visual information has become more available with the increase in multimedia platform. New cryptography scheme combines the key agreement scheme using shadow image without building a secure connection. If the many listeners listen over the public communication channel it can be immediately transmit the secret image to the other. Multi pixel encoding is an emerging method in visual cryptography where it can encode more than one pixel for encoding each encoding run. Due to the encoding length variable and small for the individual run the efficiency of encoding is still very low. Here the shadow image structure reduces the chances for an attacker to identify the secret. This given scheme involves the Deffie and Hellman and Toral autimorphism where it can be re utilized. This scheme is comfortable, easy to carry out and is safer for the shadow image. The pixel block aware encoding method is a novel multi pixel encoding method. From the experimental results it can be seen that it can easily work for the chromatic images and for the general access structure. It is provided with the excellent quality for the overlapped images and is provided high efficiency for encoding. All the discussed advantages will bring into wider applications in reality. To safeguard the images visual cryptography and the DH key agreements are used in the images which split into shadow images and will be combined rather it will transmitted this can be viewed by visual human system. This method is very secured which is provided with the encryption and decryption of images with the given key that is presented. The secondary data is preferred for the visual information while searching the related information to it where the other provided approaches cannot prove a better data. Security analysis is the important aspect in encryption process. D-H key agreement is the fundamental technology in image encryption process. The main security problems are the potential leakage during security insensible program and the bad implementation may lead to re-encrypt with same key for same password. So many proficiencies are used to encrypt the image. Transparent Encryption is most important type of computer software encryption. In this technique the data can be downloaded onto a computer to encrypt automatically. D-H key agreement is the best technique; it provides more advantages are security issues.This is a two dimensional matrix which is more preferred for detecting the locating limits in the pixels images. This also stress it view on the geometric construction of Rauzy fractals that gives the Markov partitions and the associated exchange processing.

6.2. Recommendations

Visual cryptography is a way of encrypting visual information with the help of human visual without any computer support. By this human visual system security is not provided in a proper and efficient way. More security is provided with the using encryption and decryption algorithm. Security in visual cryptography is provided by cryptographic methods with the help of visual secret key. The encryption is computationally rigorous and is done with the help of computer and the decryption is performed with little conscious effort of human visual system. For having a good encryption the image or data is divided into two parts which makes the encryption easy (Igor Fischer, 2007). As D-H key is a cool algorithm but it has no authentication. No authentication exists between sender and receiver which lead to loss of data and information can be hacked easily as both sender and receiver do not have any authentication about data. To avoid this it has to include Hash Based Message Authentication Code (HMAC) and digital signatures. The HMAC is used for calculating message authentication codes with the involvement of cryptographic hash function and secret keys. This techniques is not ideally suited for producing key which is used for encrypt data that is stored. Digital signatures help in authenticating the digital messages with some keys, by this technique the sender can send acknowledgment to the receiver about the data and vices versa (Derek Smyth, 2007). The security in D-H key exchange is given by identification of discrete logarithm problems, Diffie- hellman problems and decision Diffie hellman problems. By having a two way two way authentication securities is provided more efficiently in diffie hellman key agreement. Hence from the above context it can be concluded that more security is provided in visual cryptography by using encryption and decryption methods. Authentication is provided in D-H algorithm with the help of HMAC and with the help of digital signatures.

6.3 Future Work

As visual cryptography is type of cryptography which encodes a number of images when the images are stacked together, this can be further modified and made to more complicated way of hiding the secret images. This can be implemented by extending the scheme for color images and more flexible combination of sheets and the resulting targets. This is direct way to extend this scheme to color images. The color images can be separated to three primary colors cyan, magenta and yellow and each channel can be treated as an independent grayscale image. In a very immature approach, the system applies the encryption to each channel and merges the result to get the colored output (Mizuho Nakajima, 2002). Further applications of such schemes would be in secure distributed storage of information over a network using secret sharing to enable storage of extra information in the shares, thereby decreasing network load and increasing efficiency. Another extension is to allow flexible combination of sheets and the target images. Another best way to develop is to reverse the style of visual cryptography. For any two given secret images, two corresponding transparencies S1 and S2 which are called as shares can be produced. Both the transparencies look noisy. And then these two transparencies are stacked from front view then the first secret image in unveiled. Similarly if S1 is stacked with the back view of S2 then the second secret image is unveiled (Wen Pinn Fang, 2007). Hence it can be understood that it can be well modified and developed if it is followed as mentioned above.

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