Vol. 5, Issue 02, 2017 | ISSN (online): 2321-0613

IJSRD - International Journal for Scientific Research & Development| Vol. 5, Issue 02, 2017 | ISSN (online): 2321-0613

Image Encryption using Substitution and Discrete Cosine Transform Technique Shwetha R1 Umme Rumana2 Bindu K R3 Shashidhara S4 Prajwalasimha S N5 1,2,3,4 Student 5Assistant Professor 1,2,3,4,5 Department of Electronics & Communication Engineering 1,2,3,4,5 ATME College of engineering, Mysore, Karnataka, India Abstract— Data security in this generation is a very challenging issue that touches many areas of communication and also computers. Digital encryption has found its way has a major field of interest for development of digital image production and communication. Encryption is the process of converting normal data or plaintext to something incomprehensible. The proposed method has two phases: The pixel value is changed by non-chaotic substitution. The pixel position is changed using DCT. These two methods help to encrypt the image so it is necessary to encrypt the image before its transmission or archiving. The existing methods uses long length secrete key for the encryption process which makes the algorithm complex and time consumption is more for the execution. In this proposed method the key length is reduced to 128bit. The proposed has been designed and implemented using MATLAB software. Key words: Data Security, Digital Encryption, Communication, Chaotic and Transmission I. INTRODUCTION The image encryption is to transmit the image securely over the network so that no unauthorized user can able to decrypt the image. Encryption techniques are very useful tools to protect secret information. Encryption will be defined as the conversion of plain message into a form called a cipher text that cannot be read by any people without decrypting the encrypted text. A traditional image Encryption technique such as advanced encryption standard (AES) has the limitation of low-level effectiveness when the image size is large enough. The chaos-based image encryption scheme is a new dimensional approach and efficient way to deal with the inflexible problem. The chaos-based encryption schemes are quite popular and provide a complex cipher image, fast and highly secure.

exclusive OR operation and image dividing technique. The same grey level multi-level image is divided into binary images. Then binary pictures are regenerate to binary phase encoding and then these images are encrypt with binary random phase images by binary phase XOR operation. Prajwalasimha S N and Bhagyashree S R [2] presented an Image encryption using Discrete Random Transformation and Non chaotic Substitution. They achieved very less correlation between original and encrypted images and high entropy of the encrypted image. Fethi Belkhouche and Uvais Qidwai [3] used the method that can be used for binary images encryption with the possibility of using several keys ex: initial state, the external parameters and iterations’ number. Jiancheng Zou, Rabab K. Ward et al. [4] presented a method for new digital image scrambling method based on Fibonacci numbers. The standardization and periodicity of the scrambling transformation are discussed. The scrambling transformation has the following advantages: Encoding and decoding is very simple and they can be applied in real time situations. The scrambling effect is very sensible, the data of the image is re- distributed randomly across the whole image. The method can endure common image attacks, such as compression, noise and loss of data packet. Goutham L, Mahendra M S, Manasa A P and Prajwalasimha S N [5] presented a modified Hill Cipher Based Image Encryption Technique. They adopted substitution algorithm to improve the efficiency. Guosheng Gu and Guoqiang Han [6] made a new highly optimised image algorithm using permutation and substitution methods. It was done in order to enhance the pseudorandom characteristics of chaotic sequences, an optimized treatment and a cross-sampling disposal is used. III. METHODOLOGY

A. Problem Definition In present AES cipher technique the current size is 256 bits which require more storage, difficult to memorize and there are 14 rounds, in each round 4 steps to be followed: Substituting bytes, Shifting rows, Mixing columns, Adding round key hence the length of algorithm is more so that execution time is also more. In our proposal is just multiplication of matrix instead of performing 4 steps in each round hence we reduce the number of rounds from 14 to 6.So that the length of the algorithm is less compare to present AES technology. II. LITERATURE REVIEW Chang-Mok Shin, Dong-Hoan Seo, Kyu-Bo Chol, Ha Wmn Lee, and SmJmng Kim[1] proposed an algorithm which was multilevel form of image encryption using binary phase

Fig. 1: Block diagram of the Proposed System

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Image Encryption using Substitution and Discrete Cosine Transform Technique (IJSRD/Vol. 5/Issue 02/2017/342)

To encrypt the image following steps to be followed: 1) Read a grayscale image and converted it into suitable form. 2) The image is divided into smaller parts, say 64x64 matrix. 3) Perform non chaotic substitution for each sub matrix using secret key. 4) Combine the sub matrix to form a 256x256 matrix. 5) Apply DCT to entire image. 6) Final encrypted image. Read the 256X256 gray scale image which is in the form of JPEG(joint photographic expert group) or TIFF (tagged image file format) or other mat lab formats, and the image is divided into smaller parts say 64X64 sub matrixes and the whole 256x256 matrix contain 16 blocks of 64x64 sub matrixes. Perform initial permutation with 128bits of key, initial permutation is shuffling of key by developing 64x64 key matrix and multiply it with the divided 16 64x64 sub matrixes and the pixel position is changed by applying discrete cosine transform to entire image. Repeat the above steps up to six rounds to get the cipher image. By the side of receiver end, decrypt the image by using the same key matrix which is used in the encryption process IV. EXPERIMENTAL RESULTS The proposed algorithm has been implemented using Matlab 2013. Original images of Cameraman and Trees are shown in fig.2 and 5 respectively. Encrypted images of Cameraman and Trees are shown in the fig.3 and 6 respectively. Decrypted images of Cameraman and Tress are shown in the fig 4 & 7 respectively.

Fig. 2: Original Image

Fig. 4: Decrypted image

Fig. 3: Encrypted image

Fig. 5: Original Image

Fig. 6: Encrypted image Fig. 7 Decrypted image V. STATISTICAL ANALYSIS Sl. No.

Name of the image

Entropy of the encrypted image

Correlation coefficient between original image

and encrypted image 1 Cameraman 7.8890 0.2949 2 Trees 7.8369 0.2083 3 Moon 7.5984 0.3246 4 Tire 7.8170 0.2736 Table 1: The entropy and the correlation coefficient of the standard images are given above VI. CONCLUSION The proposed algorithm is developed to ensure the security of images during transmissions from unauthorized party. The proposed method has two phases substitution and DCT, in substitution pixel value is change where as in DCT pixel position is changed. The algorithm is subjected for different statistical analysis and found effective. REFERENCES [1] Chang-Mok Shin, Dong-Hoan Seo, Kyu-Bo Chol, HaWmn Lee, and SmJmng Kim, “ Multilevel Image Encryption by Binary Phase XOR Operations”, IEEE Proceeding in the year 2003. [2] Prajwalasimha S N and Bhagyashree S R, “Image encryption using Discrete Random Transformation and Non chaotic Substitution” proceeding of second IEEE International conference on electrical, computer and communication technologies. Feb 2017 [3] Fethi Belkhouche and Uvais Qidwai, “Binary image encoding using 1D chaotic maps”, IEEE Proceeding in the year 2003. [4] Jiancheng Zou, Rabab K. Ward, Dongxu Qi, “A New Digital Image Scrambling Method Based on Fibonacci Number,” Proceeding of the IEEE Inter Symposium On Circuits and Systems, Vancouver ,Canada ,Vol .03 , PP .965-968 , 2004. [5] Goutham L, Mahendra M S, Manasa A P and Prajwalasimha S N, “Modified Hill Cipher Based Image Encryption Technique” IJRASET, Vol.5, Issue 4, April 2017, PP.342-345. [6] Huang-Pei Xiao Guo-Ji Zhang, “An Image Encryption Scheme Based On Chaotic Systems”, IEEE Proceedings of the Fifth International Conference on Machine Learning and Cybernetics, Dalian, 13-16 August 2006. [7] M. Zeghid, M. Machhout, L. Khriji, A. Baganne,R. Tourki, “A Modified AES Based Algorithm for Image Encryption”, World Academy of Science, Engineering and Technology 27, 2007. [8] Mohammad Ali Bani Younes and Aman Jantan, “An Image Encryption Approach Using a Combination of Permutation Technique Followed by Encryption”, IJCSNS International Journal of Computer Science and Network Security, VOL 8, April 2008. [9] Amitava Nag, Jyoti Prakash Singh, Srabani Khan, Saswati Ghosh, Sushanta Biswas, D. Sarkar Partha Pratim Sarkar, “Image Encryption Using Affine Transform and XOR Operation ”,International Conference on Signal Processing, Communication, Computing and Networking Technologies (ICSCCN 2011). [10] Sesha Pallavi Indrakanti,P.S.Avadhani, “Permutation based Image Encryption Technique”, International


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Journal of Computer Applications (0975 – 8887) Volume 28 ,No.8, 2011. [11] Ibrahim S I Abuhaiba, Maaly A S Hassan, “Image Encryption Using Differential Evolution Approach In Frequency Domain” , Signal & Image Processing An International Journal (SIPIJ) Vol.2, No.1, March 2011. [12] Qiudong Sun, Wenying Yan, Jiangwei Huang, Wenxin Ma, “Image Encryption Based on Bit-plane Decomposition and Random Scrambling”, Journal of Shanghai Second Polytechnic University ,vol. 09 IEEE, 2012.


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