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  1. 1. M.Venugopal, E.G.Rajan, Dr. Sharma /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1850-1853 Pextral Coding In The Framework Of Cellular Automaton And Its Application To Visual Cryptography M.Venugopal*, E.G.Rajan**, Dr. Sharma *(Professor, Department of Electronics & Communication Engineering, HIET, R.R.District.) ** (President, Pentagram Research Center, Jubilee Hills, Hyderabad.) ** (Adrin,Hyderabad. )ABSTRACT Cryptography has gained much information from hacking/misuse. Visualimportance in the recent past due to the cryptography is one of the cryptographic techniqueadvancement in the technology for securing which allows visual information (Image, text, etc) toinformation. Visual Cryptography is such a be encrypted in such a way that the decryption can becryptographic technique through which users hide performed by the human visual system without theinformation securely based on key authentication. aid of computers. Image is a multimedia componentThis paper examines a new approach in visual sensed by human. Human visual system acts as ancryptography using pextral coding algorithm in OR function. If two transparent objects are stackedthe framework of cellular automata. Primarily a 3 together, the final stack of objects will be transparent.x 3 matrix pextral icon is considered. A 2D pextral But if any of them is non-transparent, then the finalicon is a convex polygon formed of pixels in a nine stack of objects will be non-transparent. Like OR, 0neighbourhood enclosing the central pixel. This OR 0 = 0, considering 0 as transparent and 1 OR 0=1,central pixel is similar to a pixel considered for an 0 OR 1 =1, 1 OR 1=1, considering 1 as non-image in Cryptography. Dropping one, two or transparent. In k out of n visual cryptography schemethree pixels in the given matrix forms 16 convex is a type of cryptographic technique where a digitalpolygons. Out of these 16 polygons, few will have image is divided into (n) number of shares bymirror symmetry. Two such mirror symmetry cryptographic computation. In the decryption processpolygons were considered and the central pixel of only k or more than k number of shares can reveal thethese polygons will form the image pixel. An original information [Here can form the originalalgorithm is developed to generate two signatures image]. Less than k number of shares can not revealon an ASCII image. Combining the two signatures the original information. In Visual Cryptographywill reconstruct the original image. Results show algorithms a given image are plain text is divided intothat no loss of information and improved security. (n) number of shares where minimum k numbers of shares are sufficient to reconstruct the plain textKeywords - Cryptography, Pextral Coding, image. In this paper we propose to use cellular automata of dimension 2 as graphic crypto systemsCellular Automata, ASCII Image, Authentication, i.e crypto systems to encrypt image define by pixels.Visual Cryptography. These crypto systems have several differences compared to the visual schemes proposed to date. ForI. INTRODUCTION this reason, we denote this cryptography as graphic With the advent of VLSI / Nano technology cryptography. The proposal begins with a plane textand the state of the art technology development, we message, uses a cellular automata algorithm ofhave latest smart equipment available for use. At dimension 2 and ends with encrypted message whichcertain places the security aspect plays a major role. we call as cipher image and the decryption of originalOne of the security implementation and more useful message back. The rest of this paper is organized asmethod is cryptography. During the communication follows. Below visual cryptography is reviewed inof plane text or image information between the order to compare the cellular automaton that wesource and destination cryptography is applied on propose and visual one. Some definition anddata for security reasons. Cryptography uses the key properties of cellular automata are presented in ourmatching for authentication purpose. It works on proposal of a visual representation using cellularimage or on plane text. One of the methods used to Automaton.Visual cellular automata is discussed inget the key and cipher is to incorporate nonlinearity detail and we present conclusions.in the plane text image. The smallest element of adigital image is pixel. The non linearity is achieved II. RELATED WORKby pixel expansion. Where each pixel of a plane text Shyamalendu Kandar [1] have proposed aimage is expanded into a 2 or 4 sub pixels. The non K-N secret sharing scheme for encryption usinglinearity in an image or plane text secures the random number generator. The technique is said to 1850 | P a g e
  2. 2. M.Venugopal, E.G.Rajan, Dr. Sharma /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1850-1853have less mathematical calculations with other patterns and secret sharing behaviour such atraditional techniques besides its high computational technique face problem in changing and removing thecomplexity. Sozan Abdulla [2] proposed a new watermark.cryptographic algorithm for color images by taking(n) pictures as input and generated n-1 images. IV. PROPOSED SYSTEMDecoding is performed by selecting a subset of these The proposed system overcomes the issuesn-1 images by placing them as a stack. The original present in visual cryptography by considering a newimage is same as that of the reconstructed image. approach “A Notion of pextral coding using cellularShyamalendu Kandar et. al [3] proposed a visual Automaton Algorithms”. Visual cryptography usescryptographic scheme for color images by dividing each pixel of plane text image for example ASCII „A‟the images into shares which are generated by using a and expanded to four sub pixels. The same pixelrandom number and these shares are watermarked in expansion technique is applied in cellular automaton.invisible mode. The technique proved to have lessmathematical calculation when compared to other Visual Cryptography:schemes. Pavan Kumar Gupta et. al proposed avariable length symmetric key based cryptographic Visual Cryptography is a special type ofscheme for color images based on secret key which is encryption technique to obscure image-based secretused for dividing the image into number of shares. information which can be decrypted by HumanKrishnan et. al proposed a scheme for securing color Visual System (HVS). It is a kind of secret-sharingimages. The images are protected and for encryption scheme that encrypts the secret image in to (n)as well as decryption a binary image is used as a key. number of shares. It is imperceptible to reveal theColor space models are used for decomposition of the secret information unless a certain number of sharesimages. Such a scheme is proved to be efficient in (k) or more are superimposed. As the decryptioncommunication of natural images across different process is done by human visual system, secretchannels. liu et. al proposed a color visual information can be retrieved by anyone if the personcryptographic model of Naor and Shamir without any gets at least k number of shares. The originalpixel expansion and termed it as (k,n)-VCS. Feng Liu schemes are 2 out of 2 scheme, (n ) out of (n)[7] proposed an extended VCS by taking meaningful schemes, k out of n schemes. In 2 out of 2 schemeshares which are the random shares, termed it as method, the transparencies consisting of pixels areembedded EVCS ad shown that the proposed system subdivided into 4 sub pixels. Black is opaque and theis competitive when compared to traditional White is transparent. One pixel expanded into 4 subtechniques. pixels is termed as share. The 2 out of 2 scheme has 6 possible shares.III. PROBLEM DEFINITION Security aspect plays a major role in The 2 out of 2 scheme includes creation ofprotecting the image or plane text information. Many transparencies. During creating transparencies, eachschemes were developed to safe guard the image or pixel of secrete considered separately. The firstplain text information. In certain security transparency (Key) is created randomly and theapplications, a long key of 128/256 ASCII characters second transparency (Cipher) is created dependingare divided into two keys. One of the keys is stored on the key and the secrete. Initially the white pixelson client side and other on the server side. At the are constructed and the exact matching of pixels inserver, the two keys are combined to get the original both transparencies must be achieved. Again blackkey which authenticates the user. Visual pixels are constructed and complementary pixels incryptography uses the pixel expansion to divide a both transparencies must be matched. In N out Ngiven image into number of shares. A combination of scheme, a secret is distributed over N transparenciesthese shares will get back the original image. So the and all (N) transparencies are required for decryption.long key having ASCII characters are encrypted and Pextral coding:decrypted to safe guard the information for bettersecurity. Various techniques are applied in visual Using cellular automaton, the concept of pixelencryption and decryption of plain text. PSNR of the expansion is considered using pextral codingoutput image will be less which is a setback in visual technique. Pextral coding uses a 3X3 cellular matrixcryptography. For example, when we retrieve the as shown in the figure 1.image, a white gausion noise is being added in theimage resulting in loss of contrast as white pixel isrepresented by light gray pixels and the black pixelsrepresented by dark gray pixels. In Visualcryptography, Watermark technique is anothertechnique applied for the purpose of security which Figure 1: A 3X3 cellular matrixemploys Fourier transform. Because of the random 1851 | P a g e
  3. 3. M.Venugopal, E.G.Rajan, Dr. Sharma /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1850-1853In our proposed system an ASCII „A‟ image isconsidered in a binary form as shown in the figure 2. This is the encryption technique we proposed in this paper. The decryption process uses these two signatures and combining of these signatures get back the original pixel information of the ASCII „A‟. As shown in figure 6. Figure 2: ASCII „A‟ image in 9X6 cellular matrixCellular Automaton is 2-dimensional finite method(CA for short), A= (L; S; V; f) , is a 4-uplet, where L Figure 6: Original pixel retrieval after addition ofis the cellular space formed by a 2-dimensional array signature1 and signature 2of size r _ s of identical objects called cells. ThePextral coding uses dropping of these cells in For an ASCII „A‟ image the initial pixel consideredsequence as one, two or three cells to form 16 has co-ordinates as {(i,(j+3)}as shown in figure 7.geometric patterns as shown in the figure 3. Around this co-ordinate a cellular Automaton 3X3 matrix is shown in the figure separately with its own co-ordinates dropping two cells. The other co- ordinates are {(i-1),(j+3)},{(i- 1),(j+2)},{(i),(j+3)},{(i),(j+2)}, (i+1),(j+2)}, {(i+1),(j+3)}, and {(i),(j+4)}. Figure 7: Initial pixel from ASCII „A‟ representation In these figure the pixel co-ordinate {(i-1),(j+4)} and {(i+1),(j+4)} are dropped and the remaining pixel Figure 3: 16 Geometric patterns (Polygons) information represents, the part of the signature one as shown in the figure 7 . Using this technique weTwo geometric patterns out of these 16 patterns are consider the remaining pixels in ASCII „A‟ as aconsidered as shown in the figure 4.(a) and (b) centre pixel of 3X3 cellular matrix whose co- ordinates are {(i,(j+3)}. For all the pixels of ASCII „A‟ the signature one is designed similarly as shown in the figure 7. Similarly dropping two pixels having co-ordinate {(i-1),(j+2)} and {(i+1),(j+2)}, the remaining pixel information represents the part of the signature two as shown in the figure 8. A similar technique is used by considering remaining pixels in Figure 4: Geometric patterns with symmetry ASCII „A‟ as a centre pixel of 3X3 cellular matrix.The information in ASCII „A‟ is in the form ofpixels. Each pixel of this information is consideredand expanded by the two geometric patterns byapplying pixel expansion technique similar to visualcryptography to form signature 1 and signature 2 asshown in the figure 5. (a) and (b) respectively. Figure 8: Signature 2 representation with the initial pixel from ASCII „A‟ (a) (b) Figure 5: Signature 1 and signature 2 for one pixel 1852 | P a g e
  4. 4. M.Venugopal, E.G.Rajan, Dr. Sharma /International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1850-1853V. CONCLUSION A new approach called Pextral coding usingcellular automaton is presented in this paper forencryption and decryption of an ASCII „A‟character.A pixel expansion technique similar to visualcryptography is considered and applied on cellularautomaton using pextral coding method. Pixelinformation of ASCII „A‟ is expanded and signaturesare formed for encryption. Decryption methodcombines these signatures to form the original ASCII„A‟ character. The original image and the Decryptedimage are found to be same and the peak signal tonoise ratio (PSNR) is determined and found to beinfinite indicating the absence of white Gaussiannoise in the process of encryption and decryption.REFERENCES [1] Shyamalendu Kandar, "K-N Secret Sharing Visual Cryptography Scheme for Color Image Using Random Number", International Journal of Engineering Science and Technology, Vol. 3, No. 3, March 2011. [2] Sozan Abdulla, "New Visual Cryptography Algorithm For Colored Image", Journal of Computing, Vol.2, Issue 4, APRIL 2010. [3] Shyamalendu Kandar, Arnab Maiti, Bibhas Chandra Dhara, "Visual Cryptography Scheme for Color Image Using Random Number with Enveloping by Digital Watermarking", International Journal of Computer Science Issues, Vol. 8, Issue 3, No. 1, May 2011. [4] Pavan Kumar Gupta, Naveen Hemrajani,Savita Shiwani, Ruchi Davey, "Halftone based Secret Sharing Visual Cryptographic Scheme for Color Image using Bit Analysis", International Journal of Computer Technology and Applciations, Vol 3 (1), 17-22, Jan-Feb 2012. [5] Krishnan, G.S.Loganathan, D., "Color image cryptography scheme based on visual cryptography", International Conference on Signal Processing, Communication, Computing and Networking Technologies, 404-407, 21-22 July, 2011. 1853 | P a g e