Secret Image Transmission through Image Sharing using ...transmission: key encryption, steganography and visual cryptography. Visual Cryptography is used to encrypt a secret image

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Technovision-2014: 1st International Conference at SITS, Narhe, Pune on April 5-6, 2014

All copyrights Reserved by Technovision-2014, Department of Electronics and Telecommunication Engineering,Sinhgad Institute of Technology and Science, Narhe, PunePublished by IJECCE (www.ijecce.org) 114

International Journal of Electronics Communication and Computer EngineeringVolume 5, Issue (4) July, Technovision-2014, ISSN 2249–071X

Secret Image Transmission through Image Sharingusing Secret Key and LSB EmbeddingPoonam Bidgar

M. E. Student, Department of E & TC EngineeringSITS, Narhe, Pune-41, University of Pune, India

Email: [email protected]

Neha ShahareAsst. Prof., Department of E & TC Engg.

SITS, Narhe, Pune-41, University of Pune, IndiaEmail: [email protected]

Abstract – Distribution of multimedia contents, confidentialor secret data such as military information, financialdocuments, etc has become a common practice over internet.Along with this, many malicious applications are alsoworking that are targeting financial account information anddocuments, secret images, etc. To counter such attacks, thereare three possible major common approaches for securetransmission: key encryption, steganography and visualcryptography. Visual Cryptography is used to encrypt asecret image into customized versions of the original imagewhich leads to computational complexity and also generateshares like noisy images. Steganography hides the secretimage into one innocent cover image. But, entire secret datais kept in single cover image. Combination of these threemajor approaches is also possible. So, in this paper newalgorithm is proposed which combines all these threeapproaches that will overcome problems associated withthese and provide additional security. This scheme use asymmetric secret key to encrypt the image and then secretshares of cipher image are generated by secret sharingalgorithm with steganography. So, finally experimentalresults produces meaningful stego shares of input secretimage and experimental results also show that this schemeobtains better quality of recovered original image. Use ofsecret key will ensure the security of scheme. So, this schemecan become a reliable solution suitable for today’sauthentication challenges.

Keywords – Visual Cryptography, Secure Transmission,Symmetric Key, Stego Share Images, Information Security.

I. INTRODUCTION

The Internet has become a popular communicationnetwork where the distribution of multimedia content,confidential data such as military information, financialdocuments, etc. has become a common practice. But, overInternet the information is viewed to many users. As,image is viewed by many users anyone can steal themfrom sources. In today’s information age, security of datahas become an emerging area of research that deals withall aspects of secure data communication. Hence, now thesecurity of visual information has become more and moreimportant in many real applications. To fulfill such anincreasing demand of security, many security providingtools are there in this scenario and Visual cryptography isone of them. This is introduced by Naor & Shamir in 1979to provide confidentiality and security when secret visualinformation is transmitted through unsecured

communication channels. Using secret sharing concepts,the encryption procedure encrypts a secret image intonumber of shares (printed on transparencies) which can bedistributed among group members or transmitted ordistributed over number of an untrusted communicationchannels such that only stacking of these shares can revealthe information otherwise not. Then the idea of secretsharing was also separately proposed by Adi Shamir andG. Blakley in 1979. In 1983 another method of secretsharing was proposed by Asmuth and Bloom. Shamir’sscheme is based on Polynomial Interpolation [5]. Blakleysecret sharing is based on hyper plane geometry [6].Asmuth-Bloom secret sharing scheme is based on ChineseRemainder theorem [7]. Then there are many methods toprotect sensitive data in image and Steganography is alsoone of them. This method hides a secret message in ainnocent cover medium which could be a digital image,video, audio; etc. but, the weakness of this technique isthat an entire secret data is kept in a single cover mediumand if this cover medium get lost or corrupted then thathidden data may also get corrupted. In 2004, Lin and Tsaiproposed a method that used Steganography for generationof meaningful shares with secret image sharing [8]. Thisscheme also used polynomial-based secret sharingapproach proposed by Shamir which leads to highcomputational complexity. As the decryption process isdone by human visual system, secret information can beretrieved by anyone if the person gets at least k number ofshares. So that simple visual cryptography became veryinsecure.

In this paper, a new idea is suggested which is a secretsharing method different from any of the methodsdiscussed previously. In this new method, original imagehaving secret information is going through two levels ofencryption. In first level, secret image is encrypted byusing a symmetric key based visual cryptography resultinginto new cipher image. In second level, cipher image isthen divided into no. of meaningful shares by applyingsecret sharing with steganography algorithm. Theremaining paper is organized as follows: Section 2describes related work about various previous visualcryptography schemes. Section 3 describes our proposedvisual cryptography scheme in detail. Experimental resultsare included in Section 4 and finally, Section 5 draws theconclusion.

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II. PREVIOUS WORKS

Possible ways to protect secret image based informationagainst interceptor are encryption with shared key, secretsharing of image or hiding image information in othermultimedia contents. As our new proposed idea iscombination of key encryption based visual cryptographyapproach and secret sharing with steganography approachwe briefly reviewed some of visual cryptography schemesin this section as follows. Previously, Naor and Shamirintroduced secret sharing approach [4]. Afterwards,Asmuth and Bloom proposed another secret sharingalgorithm [7]. Shamir’s secret sharing scheme is based onLagrange’s Polynomial Interpolation theorem. Thisscheme divides a secret data image into n number ofshares share1, share2……share n and these n shares areXeroxed onto n transparencies, respectively, anddistributed amongst n participants, one for eachparticipant. Such that: i) By superimposing any k or moreshares among share i transparencies together can revealthe secret information. ii) Less than k shares reveals noinformation about the secret share. This technique is called(k, n) threshold secret sharing. The (k, n) secret sharingcomes from the concept that k points are necessary todefine a polynomial of degree (k−1). Blakley Secretsharing scheme is based on hyper plane geometry [6]. It isknown that non-parallel planes intersect at a singlespecific point. This secret sharing scheme says that: i)Secret is a single point in m-dimensional space. ii) Sharecorresponds to a hyper plane. iii) Intersection of thresholdplanes gives the secret. iv) Less than threshold planes willnot reveal secret. In Asmuth-Bloom secret sharing schemeshares are created on the basis of Chinese Remaindertheorem [7]. In this, shares are generated by reductionmodulo operation and the secret is recovered by solvingthe system of congruence using the Chinese RemainderTheorem. Previously, visual cryptography was restrictedto binary images and because of this; it became inefficientin real time applications. Chang- ChouLin, Wen-HsiangTsai proposed visual cryptography for gray level imagesby dithering techniques [23]. A dithering technique is usedto convert gray level images into approximate binaryimages. Then shares are created by applying existingvisual cryptography schemes for binary images. Thelimitation in this is that all generated shares are randompatterns carrying no visual information, look like noisyimages. This scheme is still satisfactory in the aspects ofincrease in relative size and decoded image quality, evenwhen the number of gray levels in the original image stillreaches 256. Halftone Visual Cryptography was proposedby Zhi Zhou, Gonzalo R. Arce, and Giovanni DiCrescenzo [9]. In this paper, a general framework ofhalftone visual cryptography is proposed by whichvisually pleasing halftone shares, carrying significantvisual information are generated. Applying the rich theoryof blue noise halftoning into the construction mechanism

of conventional VC, the obtained visual quality is betterthan that attained by any other available VC method.Extended visual cryptography for natural images firstintroduced by Naor [3] which constructs meaningfulbinary images as shares and enables the contrastenhancement, where a simple example of (2, 2)-EVCSwas presented. This can be treated as a technique ofsteganography. There are many EVCSs proposed in theliterature [3]. Droste, Ateniese, and Wang also proposedthree EVCSs, respectively, by manipulating the sharematrices. Nakajima also proposed a (2, 2)-EVCS fornatural images. Then afterwards Embedded ExtendedVisual Cryptography Scheme was proposed by Feng Liuand Chuankun Wu and realized by embedding the randomshares into the meaningful covering shares [3]. AnExtended Visual Cryptography Algorithm for GeneralAccess Structures was proposed by Kai-Hui Lee and Pei-Ling Chiu [10]. This approach consists of two phases. Inthe first phase, they construct meaningless shares using anoptimization technique and the construction forconventional VC schemes. In the second phase, coverimages are added in each share directly by a stampingalgorithm. The experimental results indicate that thedisplay quality of the recovered image is very close to thatobtained using conventional VC schemes. Liu, C.K. WuX.J. Lin, proposed a new approach on visual cryptographyfor colored images [2] [24]. They proposed threeapproaches as follows: In first, they realize the color VCSas to print the colors in the secret image on the sharesdirectly similar to basic model. It reduces the quality of thedecoded color image. In second, a color image isconverted into black and white image or the three colorchannels (red, green, blue or equivalently cyan, magenta,yellow), respectively, and then apply the black and whiteVCS to each of the color channels which results inreduction in quality of the image due to halftone process.And in final approach they utilizes the binaryrepresentation of the color of a pixel and encrypts thesecret image at the bit-level which results in better qualitythan first two but requires devices for decryption. SharedKey Encryption of JPEG Color Images was proposed bySubramania Sudharsanan [11]. This paper mainly focuseson {2, 2} shared encryption method for JPEG images.This method creates two shares of JPEG or any formatimage. This method uses the quantized DCT coefficientsin the JPEG representation for generation of shares. Theseshares are used to reconstruct the original quantized DCTcoefficients during decryption. This offers all thecompression advantage of JPEG to all the created shareimages.

III. PROPOSED SCHEME

To transmit or store an image in a safer way againstunauthorized persons, there are at least three possiblemajor approaches: encryption with keys, hiding the image

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in other media or objects i.e, steganography, sharing ofimage among distinct parts i.e. visual cryptography.Combination of these three major approaches is alsopossible. Secret sharing of image or encryption of imagewith the help of key produce images which looks likenoisy images or textured image. So, there may be chancesthat attacker may come to know that this image is surelyencrypted image or carrying something secret data and ifhe can’t get access to that secret data, he will try to destroyit. For dealing with such problems, one can usesteganography which hides the secret information orimage into one innocent cover image that the attacker mayfails to guess whether this image contains secretinformation. But, in this entire secret data is kept in singlecover image. So, in this also there may be a chance that ifthis image may get lost or corrupted. For such problem, amethod which uses steganography for generation ofmeaningful shares can be a solution. So, we proposed anew scheme that will overcome such problems associatedwith secret image encryption. Objective of proposedscheme is to design an encryption/decryption algorithmthat efficiently provides high level security for visualinformation from illicit attacks.2.1. Encoding:

The encryption process involved in our proposedscheme is as shown in Fig.3 which includes firstlyencryption of secret image by symmetric key based visualcryptography algorithm which results in cipher imagewhich looks like noisy image and then secondly, byapplying secret sharing algorithm with steganography tokey encrypted image which results in meaningful shares.Advantage of this combined version of two schemes is thatkey encryption before secret sharing of image will giveadditional security and use of steganography in secretsharing can provide additional security as it befools theattacker’s eye without computational overhead. InEncryption process, the secret image is first of all treatedwith symmetric key [2]. This symmetric key is to begenerated with the help of symmetric key generationalgorithm [1]. After applying key, cipher image isgenerated which is then divided into n number ofmeaningful shares by applying Novel secret sharing withsteganography algorithm.2.1.1. Symmetric key generation:

Input to this algorithm is original secret image of sizen*m, any other sample image and output will be generatedsymmetric key which is then used for further part ofencryption process. Algorithm used for generation ofsymmetric key is described as follows:1. Take an image other than original secret image as input.Calculate Height (h) and Width (w) of the image and storeit in two or three dimensional image.2. Take a block of any size (e.g. - 4X2, 3X3, 4X3) withelements from array starting from left.

3. Initialize an array of size n*m*block size to hold thekey declared as Binary_Value and assign the value ofelements to zero initially.4. Now, assume the value of parameter Temp_Value andgenerate new value of element of array Binary_Value byfollowing steps: Consider, x = 1-2* Temp_Value*Temp_Value. Calculate the value of ‘x’. If value of ‘x’ isgreater than 0 then assign the value of first element ofarray Binary_Value as 1 otherwise assign it as 0. Now,Temp_Value is equal to x and repeat this procedure forfurther elements of array Binary_Value.

Fig.1. Encoding

5. Create key array using a repetitive sum method usingthe formula as:For i goes from 1 to n*mFor j goes from 1 to block size do Key[i] = Key[i] +Binary_Value [i*j] * 2 ^ (j-1).6. Arrange the value of elements of the key array using theprincipal diagonal approach and generate a twodimensional array Final_Key having n number of rowsand m number of columns.2.1.2. Encryption of Image by generated key:

In this step, Input is original secret image to beencrypted and output will be Encrypted image. Algorithmfor image encryption is described as follows:1. Perform bitwise XOR operation between original secretimage to be encrypted and generated two dimensionalFinal_Key array.2. Generate Cipher_Image from step I and print it. Thisencrypted image will look like noisy image.2.1.3. Secret Sharing of the Encrypted Image:

In this, generated Cipher_Image by applying symmetrickey is taken as input image. By appearance of thisCipher_Image interceptor may come to know that this canbe encrypted image and he will try to get data from it. Todeal with such case, our proposed scheme usesteganography which can hide image shares into coverphoto which can make interceptor fail to guess whether

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this image has hidden some secret data. For this, differentmasks are to be generated for different shares.2.1.3.1. Algorithm for designing the masks for nshares with threshold k.1. Get the value of n and k from user and form a matrix ofdimension nCk-1 × n by listing all row vectors of size nhaving the combination of (k-1) numbers of 0’s and (n-k+1) numbers of 1’s.2. Transpose the matrix generated in Step-1.Each row of this matrix will represent the individual maskfor n different shares. Thus the size of each mask is nCk-1bits, i.e. the size of the mask varies with the value of n andk. Now, use each row of this matrix for generation thecorresponding share.2.1.3.2. Actual stepwise protocol for image secretsharing scheme.

Input to this step is a key encrypted secret image i.e.Cipher_Image of size n*m generated from subsection3.2and output of this step will be n meaningful stego shareimages.1. The mask pattern is placed repeatedly on the secretimage. The bytes corresponding to 1 in the mask are keptas it is and the bytes corresponding to 0 in the mask arereplaced by 0.2. Select a pixel (say A) from cover image consisting ofthree bytes for RGB values from the corresponding coverimage then insert eight bits of masked byte (say B) intopixel byte image in such a fashion like as shown in fig.4.This forms first stego share image3. Repeat these two steps with all other mask patterns toform other stego share images respectively. So, finallyShares of key encrypted Cipher_Image covered withinnocent covers will be created by above mentionedalgorithms and they will be ready to send to intendedreceiver.3.2. Decoding:

At intended receiver, when that n no. of stego shareimages will get received then after decoding of stego shareimages will be carried out and original secret image willbe recovered. Thus, decryption process consists of stepssame as performed in encryption process but exactly inreverse order. In Decryption process, out of n receivedstego share images firstly select any k no. of share imageswhich are to be stacked.2.2.1. Bit Extraction from stego share images:

Input to this algorithm is n no. of stego share images andOutput will be recovered Cipher_Image.1. First select any k or more no of stego share images.Select the corresponding pixel and extract the share bytesBi where i= 1, 2, k from the selected k stego share images.2. Perform OR operation between these k extracted sharebytes we get the corresponding secret byte. Thus, thesecret byte is Bs = B1 OR B2 OR - - - OR Bi OR - - - ORBk3. Repeat Step II & III with all pixels of k stego images toget back the secret image of dimension*m. Finally, the

original lossless Cipher_Image will get recovered by thisalgorithm.

Fig.2. Decoding

2.2.2. Decryption using key:1. The recovered Cipher_Image is taken as input Generatethe key again for decryption process by using keygeneration step as per 3.1 algorithm explained above andretrieves Final_Key array back in this step..2. Follow XOR operation in between recoveredCipher_Image pixel array and Final_Key array. By this,finally we will get the original secret image at receiverside.

IV. EXPERIMENTAL RESULTS

In encryption process, the original secret image istreated with symmetric key in first step. Input toencryption can be any secret image either gray scale,bitmap or color image. Image in Fig. 3 is used as testimage for verifying productivity of algorithm. Afterperforming bitwise XOR operation between input secretimage and generated key the output Cipher Image is asshown below in Fig.4:

Fig.3. Input secret Image

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Fig.4. Cipher_Image

Then after getting cipher image, this image is arrangedas three planes in cell of three columns i.e, Red, Green,Blue planes of color image one by one in matrix of size1x3 for further LSB embedding (see Fig. 5). Now, in nextstep, after applying secret sharing algorithm withsteganography as discussed in section 2.1.3 to thisCipher_Image meaningful stego shares are created as likeshown below. For e.g. consider, No. of shares to becreated are: n=5. Stego share images generated at outputof encoding process are as shown below (see Fig 6 toFig.10). These images are the inputs to decoding process.

Fig.5. RGB arranged image

Fig.6. Stego Share Image 1





In decoding process, these all stego share images aretaken as input to decoding algorithm. Now, consider, atthis stage, take input data from user for Example:Minimum No. of shares required (threshold) =3, Sharesinputted: Share1, Share3, and Share4. At this, output isrecovered image with RGB rearranged image as shown inFig. 11:

Fig.11. RGB rearranged image

Then, Reconstructed Cipher_Image Image from shareswill be like this as shown in Fig.11. Now, final step ofdecryption will be decryption with key. Generate the keyand then after performing XOR operation betweenrecovered Cipher_Image pixel values and Final_Key arraywe will get original secret image as shown in fig.12. Thesealgorithms are implemented by using MATLAB R2011bsoftware.

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Fig.11. Recovered Cipher_Image

Fig.12. Reconstructed secret image

V. CONCLUSION

There are many issues about information security andconfidentiality over internet in this digital information era.To achieve maximum security to image based information,we have proposed a new method for visual cryptographydifferent from any other previous schemes. In this newproposed scheme, use of Symmetric key is suggested infirst level of encryption process of secret image which willoffer additional security. And then we are going to usesecret sharing with steganography for the creation ofshares of this encrypted image which will be meaningfulshares instead of having noise like shares. So, because ofmeaningful shares attacker may fails to guess whetherthese images contain any secret information. Experimentalresults shows that this scheme can produce meaningfulstego share images and original secret image canrecovered at receiver side with better visual quality. VisualCryptography is an exciting area of research where exists alot of scope. To best of our knowledge this scheme can bea very effective solution in providing security to secretimages from illicit attacks. Use of secret key makes itmore secure and reliable.

ACKNOWLEDGMENT

As, the process of implementation was carried out atSinhgad Institute of Science & Technology, Pune. So,

special thanks to Head of E&TC Department, Principaland Management of SITS, Pune.

REFERENCES

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Secret Image Transmission through Image Sharing using ...transmission: key encryption, steganography and visual cryptography. Visual Cryptography is used to encrypt a secret image

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