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- 1. ISSN: 2277 – 9043 International Journal of Advanced Research in Computer Science and Electronics Engineering Volume 1, Issue 2, April 2012 A RSA- DWT Based Visual Cryptographic Steganogrphy Technique Mohit Kumar Goel, Dr. Neelu Jain hours. DES and WEP are examples of two encryption Abstract— With the development of science, digital media algorithms that were thought to be secure at the time of theircan be transmitted conveniently over the internet. The security design, but were broken in the future when attackers hadof the data is essential issue for the internet. The security of more powerful computational resources. However,information can be achieved by cryptography andsteganography. Cryptography scrambles the data to hides the encryption clearly marks a message as containingcontents of message. Steganography hides the existence of “interesting” information, and the encrypted messagemessage by embedding data in some other digital media like becomes subject to attack. So, in many cases it is desirable toimage or audio files. The paper proposes a security method send information without being notice by anyone thatwhich uses both encryption and data hiding. In proposed system information has been sent. The Steganography solves thisdata is firstly encrypted using RSA encryption algorithm and problem by embedding data in the cover object so that it isthen embedded in an image using Haar-DWT basedsteganographic method. The experimental result shows that hard to detect. The word steganography in Greek meansproposed system has better PSNR value and high capacity in “covered writing” (Greek words “stegos” meaning “cover”comparison to other techniques like LSB and LSB-DCT and “grafia” meaning “writing”). Steganography differs fromsteganography. cryptography in the sense that where cryptography focuses on concealing the contents of a message, steganography Index Terms— data hiding, discrete wavelet transform, RSA focuses on concealing the existence of a message. Imageencryption, steganography. steganography schemes can be divided into two categories: Spatial Domain and Frequency Domain. I. INTRODUCTION A. Spatial domain steganography In this information era, either a public network or private In spatial domain steganography data is embedded directlynetwork, one requires a tool that can allow communicating in image pixels [4].Least Significant Bit (LSB) is the firstover these channels and as well providing the security and most widely used spatial domain steganography technique. Itrobustness of the hiding data. Encryption and steganography hides the message in the LSB of the image pixels [5]. But theare the preferred techniques for protecting the transmitted problem with this technique is that if the image is compresseddata. In Cryptography, the data is encrypted so that it cannot then the embedded data may be lost. LSB has been improvedbe understood by anyone else. The encrypted data is by using a Pseudo Random Number Generator (PRNG) and aunreadable but is not hidden from the eavesdroppers. Though secret key in order to have private access to the embeddedthe purpose of cryptography is to protect the data (or information [6]. Another recent improvement based oninformation) from unwanted attackers, it does not ensure random distribution of the message was introduced by M.covertness on the channel. The commonly used encryption Bani Younes and A. Jantan [7]. In this method they utilize anschemes include DES (Data Encryption Standard) [1], AES encryption key to hide information about horizontal and(Advanced Encryption Standard) [2] and RSA [3]. DES, an vertical blocks where the secret message bits are randomlyencryption standard that was used by many national concealed. Modulus arithmetic steganography proposed bygovernments, successfully withstood attacks for many years. Sayuthi Jaafar and Azizah A Manaf has calculated last fourHowever, E. Biham and A. Shamir mention a cryptanalytic bits of each pixel by mod-16 operation. Then these bits areattack that can break DES in only a few minutes. Another replaced with data bits [8]. In this the amount of the data thatexample of a broken encryption algorithm is WEP. WEP was can be embedded is more but stego image has less PSNRdesigned to provide confidentiality to users on wireless value than LSB and SSB-4 techniques.networks. [3] Illustrates how WEP can be broken within B. Frequency domain steganography In frequency domain, images are first transformed and Manuscript received April 15, 2012.. then the message is embedded in the image [9]. When the Mohit Kumar Goel, Electronics and Elecrical Communication data is embedded in frequency domain, the hidden dataDepartment, PEC University of Technology, Chandigarh, India , resides in more robust areas, spread across the entire image, and provides better resistance against statistical attacks. Dr. Neelu Jain, Electronics and Elecrical Communication Department, There are many techniques used to transform image fromPEC University of Technology, Chandigarh, India, spatial domain to frequency domain. The most common 95 All Rights Reserved © 2012 IJARCSEE
- 2. ISSN: 2277 – 9043 International Journal of Advanced Research in Computer Science and Electronics Engineering Volume 1, Issue 2, April 2012frequency domain method usually used in image processing 2) Public Key Cryptography: Uses one key foris the 2D discrete cosine transform (DCT) [10][11] and 2D encryption and another for decryption.discrete wavelet transform[12]. In DCT steganography the 3) Hash Functions: Uses a mathematical transformationimage is divided into 8×8 blocks and DCT transformation on to irreversibly “encrypt” information.each block is performed. The data bits are embedded in the A. RSA encryption algorithmlow frequency coefficients of DCT. SSB-4 & DCT RSA is a Public key cryptography named after itssteganography proposed by Nedal M. S. Kafri and Hani Y inventors: Ronald Rivest, Adi Shamir and Leonard Adleman.Suleiman uses DCT approach with SSB-4 technique [11]. RSA can be used for encryption as well as for authenticationThe DWT steganography uses both image‟s spatial as well as [3]. An example of Alice and Bob, who want to usefrequency characterstics. DWT divides the image in four sub asymmetric RSA algorithm for secure communication isbands (LL, LH, HL and HH) and then data can be embedded shown in fig. 1. For encryption purpose, Alice would encryptin coefficients of one of the selected sub band. the message using Bob‟s Public key and send the cipher text Steganography with cryptography can be combined so to Bob. Upon receiving the cipher text, Bob, who is owner ofthat, even if an attacker does realize that a message is sent, he corresponding private key, can then decrypt the message withwould still have to decode it [13]. Piyush Marwaha and his private key. For authentication purposes, Alice wouldParesh Marwaha use DES encryption and LSB encrypt (or sign) the message using her own private key.steganography for data security [14]. In this paper we Other people such as Bob can verify the authenticity of thepropose a method which uses RSA encryption and DWT message by using Alice‟s Public key, which is the only keysteganography for data security. that matches the signing private key. Security and robustness are the main aspects affectingsteganography and its usefulness. Security relates to theability of an eavesdropper to figure the hidden informationeasily. Robustness is concerned about the resist possibility ofmodifying or destroying the unseen data.C. PSNR (Peak Signal to Noise Ratio) PSNR computes the peak signal to noise ratio, in decibels,between two images. This ratio is used as qualitymeasurement between two images. To calculate PSNR; firstMSE is calculated as follows: 1 m1 n 1MSE I (i, j) K (i, j) mn i 0 j 0 2 (1) Where MSE is the Mean Squared Error of Original image(I) and stego image (K). Thereafter PSNR value is calculatedas follow: MAX i 2 MAX i PSNR 10. log 10 MSE 20. log 10 ( 2) Fig. 1 RSA Encryption MSE The steps for RSA algorithm are: Where, MAXi is the maximum pixel value of the image. Inother words MAXi = 2b − 1, where b is the bit depth of the 1) Select two prime numbers r, s.original image. The larger PSNR indicates the higher the 2) Calculate n= r × s and φ(n)= (r-1)(s-1)image quality i.e. there is only little difference between the 3) Select integer „e‟ such that e is relatively prime tocover-image and the stego-image. On the other hand, a φ(n).smaller PSNR means there is huge distortion between the gcd (φ (n),e)=1; 1<e < φ(n)cover-image and the stegoimage. 4) Calculate d such that d × e=1mod(φ (n)) 5) Now Public key (PU) for encryption is {e, n} and II. BACKGROUND OF CRYPTOGRPHY Private Key (PR) for decryption is {d, n}. 6) At sender side, message (M) is converted into cipher In cryptography, the message is scrambled to make it text (C) as follows:meaningless and unintelligible unless the decryption key is C= Me mod n (3)available. It makes no attempt to disguise or hide the encoded 7) At receiver side, cipher text is converted back tomessage. Basically, cryptography offers the ability of original message as follows:transmitting information between persons in a way that M= Cd mod n (4)prevents a third party from reading it. Cryptography can alsoprovide authentication for verifying the identity of someone III. HAAR- DWT TRANSFORMor something. There are several ways of classifying Wavelets are special functions which (in a formcryptographic algorithms. The three types of algorithms are: analogous to sins and cosines in Fourier analysis) are used 1) Secret Key Cryptography: Uses a single key for both as basal functions for representing signals. In addition to encryption and decryption. being an efficient, highly intuitive framework for the 96
- 3. ISSN: 2277 – 9043 International Journal of Advanced Research in Computer Science and Electronics Engineering Volume 1, Issue 2, April 2012representation and storage of multiresolution images, the frequency component of image using Haar-DWTDWT provides powerful insight into an image‟s spatial and steganography.frequency characteristics. The fourier transform and DCT,on other hand, reveal only image‟s frequency attributes.The discrete wavelet transform (DWT) used in this paper isHaar-DWT, the simplest DWT. A 2-dimensionalHaar-DWT consists of two operations which are describedas follows: Step 1: Scan the pixels from left to right in horizontaldirection and perform the addition and subtractionoperations on neighboring pixels. Store the sum on the leftand the difference on the right as shown in Figure 2. Repeatthis operation until all the rows are processed. The pixelsums represent the low frequency part (denoted as symbolL) while the pixel differences represent the high frequencypart of the original image (denoted as symbol H). Fig. 2 The horizontal operation on the first row Step 2: Scan the pixels from top to bottom in verticaldirection and perform the addition and subtraction operationson neighboring pixels. Then store the sum on the top and thedifference on the bottom as illustrated in Figure 3. Repeat this Fig. 5 Proposed Methodoperation until all the columns are processed. Finally 4sub-bands denoted as LL, HL, LH, and HH respectively are A. Embedding algorithmobtained. The LL sub-band is the low frequency portion andhence looks very similar to the original image. Steps of embedding algorithm are given as follow: Input: An M×N size cover image and data to be concealed. Output: Stego image. 1) Encrypt the plain text using RSA encryption key. 2) Perform Haar-DWT transform on cover image to decompose it into four sub bands (LL, LH, HL and HH). Fig. 3 The vertical operation 3) Apply mod2 operation on coefficients (Pi) of selected The first-order 2-D Haar-DWT applied on the image sub band (LH) and modify it to hide data (mi) in“woman” is illustrated in Fig 4. following way: Qi = mod2 (Pi) a) If Qi is 0 i.e. Pi is even then Modified coefficients MPi = Pi+ mi or b) If Qi is 1 i.e. Pi is odd then Modified coefficients MPi = (Pi-1) + mi 4) Four sub bands including modified sub band are combined to generate stego image using Haar- Fig. 4 Haar DWT Operation IDWT transform. 5) Send the stego image to receiver. IV. PROPOSED METHOD The challenge in this work was to find a way to B. Extraction algorithmcamouflage a secret message in an image without perceptible Steps for extraction algorithm are given as follows:degrading the image quality and to provide better resistanceagainst steganalysis process. The data is first converted into Input: An M×N size Stego image.cipher text using RSA encryption and the hided into lower Output: Secret message. 97 All Rights Reserved © 2012 IJARCSEE
- 4. ISSN: 2277 – 9043 International Journal of Advanced Research in Computer Science and Electronics Engineering Volume 1, Issue 2, April 2012 1) Perform Haar-DWT transform on stego image to Table 1. Comparative analysis of PSNR values of different decompose it into four sub bands (LL, LH, HL and steganography techniques HH). PSNR Value Image 2) Apply mod2 operation on coefficients (Pi) of selected LSB LSB-DCT RSA & DWT sub band (LH) to extract data (mi) in following way: animal.jpg 52.62 54.66 55.87 Qi = mod2 (Pi) human.jpg 53.31 55.24 57.36 Message bit mi = Qi 3) Concatenate the message bits to obtain cipher message. building.jpg 53.12 54.46 56.52 4) Decrypt the cipher message using RSA decryption keys flower.jpg 52.78 54.86 56.35 and display it on screen. VI. CONCLUSION V. EXPERIMENTAL RESULTS In this paper we used a mixed approach cryptography and Since the visual detection of stego images is depending on steganography is used for data security. By using RSAthe nature of the image [15] so, varieties of image categories encryption, ASCII codes corresponding to characters of plainare utilized in the experiments. The experimental image data text are converted into 16 bits encrypted codes. Hence itset consists of 100 JPEG images, which were taken by digital becomes difficult to get original text without knowingcamera. We focused on short messages with length of 3000 decryption keys. Then cipher data is hided into cover image.bits because they are the most challenging to detect [15]. Average PSNR value of 56 is obtained for 100 images using proposed method. The obtained experimental results indicate that, the proposed method is a good and acceptable scheme for data security. Furthermore, by embedding information in the least significant bits of the DWT domain, the hidden message resides in more robust areas, spread across the entire stego image, and provides better resistance against statistical attacks than other techniques. The future work may focus on(a) Original animal.jpg (b) Stego animal.jpg the improvement and further development in this technique. REFERENCES [1] DES Encryption Standard (DES), National Bureau of Standard (U.S.). Federal Information Processing Standards Publication 46, National Technical Information Service, Springfield, VA, 1997. [2] Daemen J., and Rijmen, V. “Rijndael: The Advanced Encryption Standard”, Dr. Dobb‟s Journal, March 2001. [3] R. Rivest, A. Shamir, and L. Adleman, “A method for obtaining digital signatures and public-key cryptosystems”. Communication of the(c) Original human.jpg (d) Stego human.jpg ACM, pp. 120-126, 1978. [4] Chan, C.K. and Cheng. L.M. “Hiding data in image by simple LSB substitution. Pattern Recognition”, 37, pp. 469 – 474, 2004. [5] N. Nikolaidis, and I. Pitas, “Robust Image Watermarking in the Spatial Domain”, Signal Processing, 66(3), pp. 385-403, 1998 [6] J. Fridrich, M. Goljan, “ Steganalysis of JPEG Images: Breaking the F5 Algorithm”, Publisher: Springer Berlin, Heidelberg, Lecture Notes in Computer Science, vol. 2578, pp 310-323, 2003. [7] M. A. Bani Younes, A. Jantan, “A New Steganography Approach for Image Encryption Exchange by Using the Least Significant Bit(e) Original building.jpg (f) Stego building.jpg Insertion”, IJCSNS, International Journal of Computer Science and Network Security, vol. 8 No. 6, June 2008. [8] Sayuthi Jaafar, Azizah A Manaf, Akram M Zeki, “Steganography Technique using Modulus Arithmetic”, 9th International Symposium on Signal Processing and Its Applications, pp. 1 – 4, April 2007. [9] Iwata M., Miyake K., and Shiozaki, “Digital Steganography Utilizing Features of JPEG Images”, IEICE Transfusion Fundamentals, E87-A, 4, pp. 929 – 936, 2004. [10] M. Kharrazi, H. Sencar, and N. Memon, “Performance study of common image steganography and steganalysis techniques,”(g) Original flower.jpg (h) Stego flower.jpg Communications of the SPIE and IS&T, 15, No.4, pp. 1017-9909, Oct-Dec., 2006.Fig. 6 Original Images and Stego Images using DCT steganography [11] Nedal M.S. Kafari, Hani Y. Suleiman, “Bit-4 of Frequency Domain DCT Steganography Technique”, First National Conference on Comparative analysis of LSB, LSB-DCT, and proposed Network Digital Technologies, PP. 286-291, 2009.method has been done on the basis of Peak signal to noise [12] Amitava Nag, Sushanta Biswas and Debasree Sarkar, “A Novel Technique for Image Steganography Based on DWT and Huffmanratio (PSNR). The comparative analysis of PSNR value of Encoding”, International Journal of Computer Science and Security,different steanography technique, is given in table 1, shows (IJCSS), vol. 4, pp. 561-570, 2011that proposed method of steganography has better image [13] Wai Wai Zin, Than Naing Soe, “Implementation and Analysis of Three Steganographic Approaches”, Proceedings of 3rd Internationalquality of stego image than other techniques. conference on Computer Research and Development (ICCRD), 2011, vol. 2, p.p. 456-460. 98
- 5. ISSN: 2277 – 9043 International Journal of Advanced Research in Computer Science and Electronics Engineering Volume 1, Issue 2, April 2012[14] Piyush Marwaha, Paresh Marwaha, “Visual cryptographic steganography in images”, Proceedings of international conference on Computing Communication and Networking Technologies, 2010, p.p. 1-6.[15] L. Davidson, and P. Goutam, “Locating secret message in images”, In ACM SIGKDD international conference on Knowledge discovery and data mining, (Seattle, Washington, Aug.22-25. ACM 1-58113-888-1, 2004.[16] Gonzalez, R.C. and Woods, R.E., Digital Image Processing using MATLAB, Pearson Education, India,2006. 99 All Rights Reserved © 2012 IJARCSEE

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