136 JOURNAL OF EMERGING TECHNOLOGIES IN WEB INTELLIGENCE, VOL. 2, NO. 2, MAY 2010[9] https://www1.gotomeet<strong>in</strong>g.com/?Portal=www.gotomeet<strong>in</strong>g.com[10] http://www.ibm.com/lotus/sametime[11] http://www.meet<strong>in</strong>gbridge.com/[12] http://www.readytalk.com/[13] http://www.webmeetlive.com/Anuradha Verma is currently work<strong>in</strong>g as TechnicalEvangelist <strong>in</strong> the Education & Research Department at Infosys<strong>Technologies</strong> Ltd. She has over 6 years <strong>of</strong> IT Industryexperience cover<strong>in</strong>g areas like Tra<strong>in</strong><strong>in</strong>g & Development,Test<strong>in</strong>g, S<strong>of</strong>tware Development and Industry-AcademiaPartnership.She has Masters <strong>in</strong> Bus<strong>in</strong>ess Adm<strong>in</strong>istration along with aMasters <strong>in</strong> <strong>Journal</strong>ism and Mass Communication. She iscurrently pursu<strong>in</strong>g her Doctor <strong>of</strong> Philosophy <strong>in</strong> Managementwith Human Resource Specialization. She has authoredpublications <strong>in</strong> International Conferences and <strong>Journal</strong>.Anoop S<strong>in</strong>gh. At Infosys, Anoop S<strong>in</strong>gh is currently work<strong>in</strong>gas GROUP LEADER <strong>in</strong> the E&R Department. He has over 12years <strong>of</strong> IT Industry experience <strong>in</strong>clud<strong>in</strong>g 4 years <strong>of</strong> exposure <strong>in</strong>global market, work<strong>in</strong>g <strong>in</strong> various counties <strong>of</strong> South East Asiaregion like S<strong>in</strong>gapore, Hong Kong and Ch<strong>in</strong>a. Anoop hasextensive IT Industry experience cover<strong>in</strong>g areas like Tra<strong>in</strong><strong>in</strong>g &Development, Bus<strong>in</strong>ess Partner Development, Product L<strong>in</strong>emanagement and Industry-Academia Partnership.Anoop has earlier worked with IT organizations like NIIT,NIIT Shanghai Ltd. and have server large global customer likeMicros<strong>of</strong>t, S<strong>in</strong>gapore Airl<strong>in</strong>e, Beij<strong>in</strong>g International Airport andvarious Ch<strong>in</strong>ese universities. He has worked on technologiesareas like Database, Network Design and various programm<strong>in</strong>glanguages. Anoop also holds a Master’s Degree <strong>in</strong> InformationScience.© 2010 ACADEMY PUBLISHER
JOURNAL OF EMERGING TECHNOLOGIES IN WEB INTELLIGENCE, VOL. 2, NO. 2, MAY 2010 137Efficient Visual CryptographyEr. Supriya K<strong>in</strong>gerCSE Department, Chitkara Institute <strong>of</strong> Eng<strong>in</strong>eer<strong>in</strong>g and Technology,Rajpura, Punjab, IndiaEmail: ahujasupriya@gmail.comAbstract – Visual cryptography scheme (VCS) is a secretshar<strong>in</strong>gscheme which allows the encryption <strong>of</strong> a secretimage <strong>in</strong>to n shares that are distributed to n participants.The beauty <strong>of</strong> such a scheme is that, the decryption <strong>of</strong> thesecret image requires neither the knowledge <strong>of</strong>cryptography nor complex computation. Colour visualcryptography becomes an <strong>in</strong>terest<strong>in</strong>g research topic afterthe formal <strong>in</strong>troduction <strong>of</strong> visual cryptography by Naor andShamir <strong>in</strong> 1995. It is a powerful technique which comb<strong>in</strong>esthe notions <strong>of</strong> perfect ciphers and secret shar<strong>in</strong>g <strong>in</strong>cryptography with that <strong>of</strong> raster graphics. A b<strong>in</strong>ary imagecan be divided <strong>in</strong>to shares which can be stacked together toapproximately recover the orig<strong>in</strong>al image. Unfortunately, ithas not been used much primarily because the decryptionprocess entails a severe degradation <strong>in</strong> image quality <strong>in</strong>terms <strong>of</strong> loss <strong>of</strong> resolution and contrast. Its usage is alsohampered by the lack <strong>of</strong> proper techniques for handl<strong>in</strong>ggrayscale and color images. In this paper, I have developeda novel technique which enables visual cryptography <strong>of</strong>color as well as grayscale images. The physical transparencystack<strong>in</strong>g type <strong>of</strong> decryption allows for the recovery <strong>of</strong> thetraditional visual cryptography quality image. An enhancedstack<strong>in</strong>g technique allows for the decryption <strong>in</strong>to a halftonequality image. And f<strong>in</strong>ally, a computation based decryptionscheme makes the perfect recovery <strong>of</strong> the orig<strong>in</strong>al imagepossible. Based on this basic scheme, I have then establisheda progressive mechanism to share color images at multipleresolutions. I extracted shares from each resolution layer toconstruct a hierarchical structure; the images <strong>of</strong> differentresolutions can then be restored by stack<strong>in</strong>g the differentshared images together. I have implemented our techniqueand present results.Index Terms – Secret shar<strong>in</strong>g, Color halfton<strong>in</strong>g, imageshar<strong>in</strong>g, multiple resolutions, secret shar<strong>in</strong>g, and visualcryptographyI. INTRODUCTIONVisual cryptography was orig<strong>in</strong>ally proposed for theproblem <strong>of</strong> secret shar<strong>in</strong>g. Secret shar<strong>in</strong>g is one <strong>of</strong> theearly problems to be considered <strong>in</strong> cryptography. Theidea <strong>of</strong> the visual cryptography model proposed <strong>in</strong> [1] isto split an image <strong>in</strong>to two random shares (pr<strong>in</strong>ted ontransparencies) which separately reveal no <strong>in</strong>formationabout the orig<strong>in</strong>al secret image other than the size <strong>of</strong> thesecret image. The image is composed <strong>of</strong> black and whitepixels. The orig<strong>in</strong>al image can be recovered bysuperimpos<strong>in</strong>g the two shares. The underly<strong>in</strong>g operation<strong>of</strong> this visual cryptography model is OR.Visual cryptography is a unique technique <strong>in</strong> thesense that the encrypted messages can be decrypteddirectly by the human visual system. Therefore, a systememploy<strong>in</strong>g visual cryptography can be used by anyonewithout any knowledge <strong>of</strong> cryptography. Another<strong>in</strong>terest<strong>in</strong>g th<strong>in</strong>g about visual cryptography is that it is aperfectly secure cipher. There is a simple analogy <strong>of</strong> theone time-pad cipher to visual cryptography.II. BACKGROUND ON VISUAL CRYPTOGRAPHYBesides <strong>in</strong>troduc<strong>in</strong>g the new paradigm, Naor andShamir also provided their constructions <strong>of</strong> visualcryptographic solutions for the general k out <strong>of</strong> n secretshar<strong>in</strong>g problem. One can assume that every secretmessage can be represented as an image, and furthermorethat the image is just a collection <strong>of</strong> black and whitepixels i.e. it is assumed to be a b<strong>in</strong>ary image. Eachorig<strong>in</strong>al pixel appears <strong>in</strong> n modified versions (calledshares) <strong>of</strong> the image, one for each transparency. Eachshare consists <strong>of</strong> m black and white sub-pixels. Eachshare <strong>of</strong> sub-pixels is pr<strong>in</strong>ted on the transparency <strong>in</strong> closeproximity (to best aid the human perception, they aretypically arranged together to form a square with mselected as a square number). The result<strong>in</strong>g structure canbe described by a Boolean matrix M = (m i j ) n*m where m i j= 1 if and only if the j-th sub-pixel <strong>of</strong> the i-th share(transparency) is black. The important parameters <strong>of</strong> thescheme are:1. m, the number <strong>of</strong> pixels <strong>in</strong> a share. Thisparameter represents the loss <strong>in</strong> resolution fromthe orig<strong>in</strong>al image to the recovered one.2. α, the relative difference <strong>in</strong> the weight betweenthe comb<strong>in</strong>ed shares that come from a whitepixel and a black pixel <strong>in</strong> the orig<strong>in</strong>al image.This parameter represents the loss <strong>in</strong> contrast.3. γ, the size <strong>of</strong> the collection <strong>of</strong> C 0 and C 1 . C 0refers to the sub-pixel patterns <strong>in</strong> the shares fora white pixel and black refers to the sub-pixelpatterns <strong>in</strong> the shares for the 1 pixel.The constructions can be clearly illustrated by a 2 out<strong>of</strong> 2 visual cryptographic scheme. Here we def<strong>in</strong>e thefollow<strong>in</strong>g collections <strong>of</strong> 2*4 matrices:C 0 = all the matrices obta<strong>in</strong>ed by permut<strong>in</strong>g thecolumns <strong>of</strong>1 1 0 01 1 0 0C 1 = all the matrices obta<strong>in</strong>ed by permut<strong>in</strong>g thecolumns <strong>of</strong>1 1 0 00 0 1 1© 2010 ACADEMY PUBLISHERdoi:10.4304/jetwi.2.2.137-141
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