International Journal of Computer, Electronics & Electrical Engineering (ISSN: 2249 - 9997)Volume 2– Issue 2 A Novel Visual Cryptographic Steganography Technique Mohit Kumar Goel *, Dr. Neelu Jain # * Dept. of Electronics and Electrical Comm., PEC University of Technology, Chandigarh mohitgoel4u@gmail.com # Dept. of Electronics and Electrical Comm., PEC University of Technology, Chandigarh neelujain@pec.ac.in Abstract— With development in technologies, the amount of data being exchanged on internet is increasing exponentially. The security of information can be achieved by cryptography and steganography. Cryptography hides the contents of message by converting it to an unreadable cipher. Steganography hides the existence of message by embedding data in some other digital media like image or audio files. The paper proposes a security system which is combination of both the techniques. In proposed system data is firstly encrypted using RSA encryption algorithm and then embedded in an image using DCT based steganographic method. The experimental result shows that proposed system has better PSNR value in comparison to other techniques like LSB, Modulus arithmetic steganography. It also maintainstaisfactory security as secret message can’t be extracted without knowing the decoding algorithm. Keywords- steganography; RSA encryption; data hiding; discrete cosine transform. conceal the secret messages within some image, music or I. INTRODUCTION audio file so that it is not visible to others. Image Due to increasing the technologies, security systems are steganography schemes can be divided into two categories: very popular in many areas. The information comes in Spatial Domain and Frequency Domain. numerous forms and requires secure communication. Such secure communication ranges from bank transactions, A. Spatial domain steganography corporate communications and credit card purchases. Spatial domain techniques embed messages in the Encryption and steganography are the preferred techniques intensity of the pixels directly [6][7][8]. Least Significant for protecting the transmitted data. Encryption hides the Bit (LSB) is the first most widely used spatial domain contents of the message, but cannot hide the message data steganography technique. It embeds the bits of a message in itself. However, encryption clearly marks a message as the LSB of the image pixels [9][10]. But the problem with containing “interesting” information, and the encrypted this technique is that if the image is compressed then the message becomes subject to attack. The commonly used embedded data may be lost. Thus, there is a fear for loss of encryption schemes include DES (Data Encryption data that may have sensitive information [11]. LSB has been Standard) [1], AES (Advanced Encryption Standard) [2] and improved by using a Pseudo Random Number Generator RSA [3]. DES, an encryption standard that was used by (PRNG) and a secret key in order to have private access to many national governments, successfully withstood attacks the embedded information [12]. The embedding process for many years. However, E. Biham and A. Shamir mention starts with deriving a seed for a PRNG from the user a cryptanalytic attack that can break DES in only a few password and generating a random walk through the cover minutes [4]. Another example of a broken encryption image that makes the steganalysis hard. Another recent algorithm is WEP. WEP was designed to provide improvement based on random distribution of the message confidentiality to users on wireless networks. A. was introduced by M. Bani Younes and A. Jantan [13]. In Stubblefield illustrates how WEP can be broken within this method they utilize an encryption key to hide hours [5]. DES and WEP are examples of two encryption information about horizontal and vertical blocks where the algorithms that were thought to be secure at the time of their secret message bits are randomly concealed. SSB-4 design, but were broken in the future when attackers had steganography approach introduced by Rodrigues, Rios and more powerful computational resources. So, in many cases Puech is about changing the 4th bit of a pixel in the original it is desirable to send information without being notice by image according to the bit message. Then modify the other anyone that information has been sent. Steganography bits (1st, 2nd, 3rd and/or 5th) to minimize the difference www.ijceee.org Page 39 International Journal of Computer, Electronics & Electrical Engineering (ISSN: 2249 - 9997)Volume 2– Issue 2 between the changed pixel value and the original one [14]. 3) Hash Functions: Uses a mathematical The 4th digit is a significant bit and if the image is transformation to irreversibly “encrypt” compressed the embedded information is not destroyed [15]. information. Tu C. and Tran T D. argued that the difference must be A. RSA encryption algorithm equal or less than four (i.e., ±4) [16]. The 4th bit was chosen because it satisfies that changing of ±4 units in the channel RSA is a Public key cryptography named after its color value is imperceptible to human eyes, and it is the inventors: Ronald Rivest, Adi Shamir and Leonard Adleman. most significant bit which provides the minimum change in RSA can be used for encryption as well as for authentication the pixel values. Modulus arithmetic steganography [3]. An example of Alice and Bob, who want to use proposed by Sayuthi Jaafar and Azizah A Manaf has asymmetric RSA algorithm for secure communication is calculated last four bits of each pixel by mod-16 operation. shown in fig. 1. For encryption purpose, Alice would encrypt Then these bits are replaced with data bits [8]. In this the the message using Bob’s Public key and send the cipher text amount of the data that can be embedded is more but stego to Bob. Upon receiving the cipher text, Bob, who is owner of image has less PSNR value than LSB and SSB-4 corresponding private key, can then decrypt the message techniques. with his private key. For authentication purposes, Alice would encrypt (or sign) the message using her own private B. Frequency domain steganography key. Other people such as Bob can verify the authenticity of the message by using Alice’s Public key, which is the only In frequency domain, images are first transformed and key that matches the signing private key. then the message is embedded in the image [17][18][19]. When the data is embedded in frequency domain, the hidden data resides in more robust areas, spread across the entire image, and provides better resistance against statistical attacks. There are many techniques used to transform image from spatial domain to frequency domain. The most common frequency domain method usually used in image processing is the 2D discrete cosine transform [20][21]. In this technique the image is divided into 8×8 blocks and DCT transformation on each block is performed. The data bits are embedded in the low frequency coefficients of DCT. SSB-4 & DCT steganography proposed by Nedal M. S. Kafri and Hani Y Suleiman uses DCT approach with SSB-4 technique [21]. Steganography with cryptography can be combined so that, even if an attacker does realize that a message is sent, he would still have to decode it [26]. Piyush Marwaha and Paresh Marwaha use DES encryption and LSB steganography for data security [25]. In this paper we propose a method which uses RSA encryption and LSB- DCT steganography for data security. II. BACKGROUND OF CRYPTOGRAPHY Figure 1. RSA Encryption In cryptography, the message is scrambled to make it meaningless and unintelligible unless the decryption key is The steps for RSA algorithm are: available. It makes no attempt to disguise or hide the 1) Select two prime numbers p, q. encoded message. Basically, cryptography offers the ability 2) Calculate n= p × q and (n)= (p-1)(q-1) of transmitting information between persons in a way that 3) Select integer ‘e’ such that prevents a third party from reading it. Cryptography can also provide authentication for verifying the identity of gcd ( (n),e)=1; 1<e < (n) someone or something. There are several ways of 4) Calculate d such that d × e=1mod( (n)) classifying cryptographic algorithms. The three types of 5) Now Public key (PU) is {e, n} and Private algorithms are: Key (PR) is {d, n}. 6) At sender side, message (M) to be sent is 1) Secret Key Cryptography: Uses a single key for converted into cipher text (C) as follows: both encryption and decryption. C= Me mod n (1) 2) Public Key Cryptography: Uses one key for 7) At receiver side, cipher text is converted to original encryption and another for decryption. message as follows: M= Cd mod n (2) www.ijceee.org Page 40 International Journal of Computer, Electronics & Electrical Engineering (ISSN: 2249 - 9997)Volume 2– Issue 2 III. LSB-DCT STEGANOGRAPHY DCT is performed on each block. Then scan the DCT block in zigzag way and extract the embedded data. LSB-DCT steganography image (I) is divided into 8x8 blocks and two dimensional (2-D) is performed on each IV. PROPOSED METHOD block. The 2-d DCT is calculated as follow: The challenge in this work was to find a way to 1 7 7 π(2x +1)u π(2y +1) camouflage a secret message in an image without F(u, v) = C(u)C(v) f (x, y)cos cos (3) perceptible degrading the image quality and to provide 4 x=0 y=0 16 16 better resistance against the steganalysis process. The data is for x=0,..., 7 and y=0,..,7 first converted into cipher text using RSA encryption and then hided into lower frequency components of image using 1 / 2 for k = 0 LSB-DCT steganography. where C ( k ) = 1 otherwise A. Embedding algorithm In DCT block lower frequency cofficents are at upper Steps of embedding algorithm are given as follow: left positions and high frequency coefficients are lower right positions. Now image is compressed by quantization. Input: An M×N size cover image and data to be concealed. Quantization is achieved by dividing each element in the DCT coefficient block by the corresponding value in the Output: Stego image. standard quantization matrix shown in fig. 2 and the result is 1) Encrypt the plain text using encryption key. rounded to the nearest integer. As eye is not able to discern 2) Divide the cover image into 8×8 blocks. the change in high frequency components so these can be 3) Perform 2-D DCT on each block. compressed to larger extent. Lower right side components of 4) Perform quantization on each block. quantization matrix are of high value so that after 5) Perform zigzag scan to convert 8×8 block into one quantization high frequency components become zero. dimensional array. 16 11 10 16 24 40 51 61 6) Replace the LSB of DCT coefficients with data 12 12 14 19 26 58 60 55 bits. 14 13 16 24 40 57 69 56 7) Convert 1-D zigzag array back to 8×8 block. 8) Perform Inverse DCT on each block. 14 17 22 29 51 87 80 62 Q= 9) Combine all the blocks to form stego image. 18 22 37 56 68 109 103 77 24 35 55 64 81 104 113 92 49 64 78 87 103 121 120 101 72 92 95 98 112 100 103 99 Figure 2. Quantization Matrix Although the DCT coefficients have been decorrelated by DCT transform to some extent, DCT coefficients in the same block are still not independent, which is called as intra-block correlation [16]. While neglecting the impact of block edge, the general trend in magnitude of the block coefficients in each block is non-increasing along zigzag scan order. After block DCT coefficients are arranged by zigzag scan pattern, dependencies among neighboring coefficients in both horizontal and vertical directions can be conveniently investigated [23]. Now data is embedded in one dimensional zigzag array a) If data bit is ‘0’, then make the DCT coefficient even or, b) If the data bit is ‘1’, then make the DCT coefficient odd After embedding data zigzag array is again converted into 8×8 block. These blocks are dequantized and inverse Figure 3. Proposed Method DCT is performed. The entire 8×8 blocks are combined to form the stego image which is then sent to receiver. B. Extraction algorithm At the receiver side the stego-image is received in spatial Steps for extraction algorithm are given as follows: domain. Now stego image is divided into 8×8 blocks and Input: An M×N size Stego image. www.ijceee.org Page 41 International Journal of Computer, Electronics & Electrical Engineering (ISSN: 2249 - 9997)Volume 2– Issue 2 Output: Secret message. (c) Original Flower.jpg (d) Stego Flower.jpg 1) Divide the stego image into 8×8 blocks. 2) Perform 2-D DCT on each block. 3) Perform quantization on each block. 4) Perform zigzag scan to convert 8×8 block into one dimensional array. 5) Check the DCT coefficient. a) If DCT coefficient is even then data bit is 0 or, b) If DCT coefficient is odd then data bit is 1. (e) Original Building.jpg (f) Stego Building.jpg 6) Concatenate the bits to obtain cipher message. 7) Decrypt the cipher text using decryption keys and display original message on screen. V. EXPERIMENTAL RESULTS Since the visual detection of stego images is depending on the nature of the image [24] so, varieties of image categories are utilized in the experiments. The experimental image data set consists of 100 JPEG images, which were (g) Original Tree.jpg (h) Stego Tree.jpg taken by digital camera. We focused on short messages with length of 3000 bits because they are the most challenging to Figure 4. Original Images and Stego Images using DCT steganography detect [24]. Comparative analysis of LSB, Modulus The comparative analysis of PSNR value of different arithmetic (mod-16), and proposed method has been done steanography technique, is given in table 1, shows that on the basis of Peak signal to noise ratio (PSNR). To proposed steganography method has better image quality of calculate PSNR, first MSE is calculated as follows: stego image than other techniques. 1 m −1 n −1 2 Table 1. Comparative analysis of PSNR values of different steganography MSE = I (i , j ) − K ( i , j ) ( 4) techniques mn i =0 j =0 PSNR Value Where MSE is the Mean Squared Error of Original image (I) and stego image (K). Thereafter PSNR value is Image Modulus RSA & LSB- LSB calculated as follow: (mod-16) DCT 55.87 MAX i2 MAX i Human.jpg 52.10 49.23 PSNR = 10. log10 = 20. log10 (5) MSE MSE 56.36 Flower.jpg 53.54 50.53 Where, MAXi is the maximum pixel value of the image. 54.59 In other words MAXi = 2b − 1, where b is the bit depth of Building.jpg 52.43 48.77 the original image. PSNR computes the peak signal to noise 55.57 ratio, in decibels, between two images. This ratio is used as Tree.jpg 53.46 50.46 quality measurement between two images. V. CONCLUSION In this paper we used mixed approach cryptography and steganography is used for data security. By using RSA encryption, ASCII codes corresponding to characters of plain text are converted into 16 bits encrypted codes. Hence it becomes difficult to get original text without knowing decryption keys. Then cipher data is hided into cover image. Average PSNR value of 55 is obtained for 100 images using (a) Original Human.jpg (b) Stego Human.jpg 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 DCT 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 the improvement and further development in this technique. www.ijceee.org Page 42 International Journal of Computer, Electronics & Electrical Engineering (ISSN: 2249 - 9997)Volume 2– Issue 2 VI. REFERENCES [15] J. Fridrich, and M. Goljan, “Practical steganalysis: state-of the-art”, In Proceeding of SPIE Photonics West, Electronic Imaging 2002, vol. [1] DES Encryption Standard (DES), National Bureau of Standard (U.S.). 4675, pp. 1-13, 2002. 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