978-1-5090-3239-6/17/$31.00©2017IEEE Image Encryption using Discrete Radon Transformation and Non chaotic Substitution Prajwalasimha S N 1 Assistant Professor Dept. of Electronics and Communication Engineering ATME College of Engineering, Mysore Karnataka, India prajwalasimha.sn@atme.in Bhagyashree S R 2 Associate Professor & Head, Member, IEEE Dept. of Electronics and Communication Engineering ATME College of Engineering, Mysore Karnataka, India bhagyashree.sr@atme.in Abstract—In this paper, transformation and substitution based symmetric key encryption algorithm is proposed. Strong correlation between the adjacent pixels can be observed in the multimedia images. The encryption can be made effective by changing both position and value of each pixel in the image. In the proposed algorithm, each pixel position is scrambled using discrete radon transformation (DRT) and pixel value is varied using non chaotic substitution and permutation. The key length used is 64 bits. The secrete key is divided into eight separate keys each of length 8 bits and these are used to change the pixel position along with DRT. Simultaneously, the secret key is subjected for eight set of initial permutations and each set is used to change the pixel value of the image using exclusive-OR operation. Keywords— Symmetric key encryption; Correlation; Discrete Radon Transformation; Non chaotic substitution; Exclusive-OR I. INTRODUCTION A secured information transaction system is required for day to day multimedia communication. Hiding the original information by an apparent (cipher) is the major task for peer to peer data transaction. In cryptography and steganography, there are plenty of methods available for hiding the text as well as multimedia data. The encryption involves the conversion of original data into cipher data and the decryption is the inverse process of encryption. The encryption technique is widely classified into two classes: symmetric key encryption and asymmetric key encryption. The key used in the symmetric key encryption technique is same for both encryption as well as decryption and different keys are used for both encryption and decryption in asymmetric key encryption process. Multimedia data are characterized with high redundancy. Each pixel value is strongly correlated with the neighboring pixels. The most popular encryption algorithms such as DES, AES, RSA and IDES are efficiently applicable for text data [1]. Image encryption involves two major process: change in the pixel position and change in the pixel value. Both value transformation and position permutation are adopted in the proposed algorithm where value transformation is performed using DRT and position permutation is made using non chaotic substitution techniques. II. RELATED WORK Digital image encryption technique involves three major classes: position permutation, value transformation and visual transformation. Affine transformation based digital image encryption system has been described by Amitava Nag, Jyoti Prakash Singh, Srabani Khan and Saswati Ghosh [1]. The pixel position is shuffled by affine transformation and the pixel value is altered by XOR operation. The key length used is considerably less compared to other transformation algorithms. Encryption of multimedia data based on discrete chaotic map has been proposed by Salwa K. Abd-El-Hafiz, Sherif H. AbdElHaleem and Ahmed G. Radwan [2]. In this paper, they explained three different permutation techniques to achieve shannon's confusion and diffusion properties. In fractional Fourier transformation based image encryption algorithm, the image is divided into number of blocks and then each block is subjected for transformation [3]. Ahmed G. Radwana, Sherif H. AbdElHaleema and Salwa K. Abd-El- Hafiza presented non chaotic substitution and permutation method of image encryption. Fractal and chess based substitution and permutation methods has been adopted to change both pixel position and pixel value [4]. In hyper chaotic system based text and image encryption technique, the secret key is first subjected for hyper chaotic generator which performs permutation such that bruit force attack can be resisted for some extent [5]. Adrian-Viorel Diaconu, Valeriu Ionescu, Gabriel Iana and Jose Manuel Lopez-Guede has presented bit level permutation based image encryption technique [6]. In quick Response (QR) code based image encryption, discrete wavelet transformation is used for embedding QR code [7]. Image encryption can also be done using matrix transformation [8]. Self-invertible randomly generated matrix is used as encryption key. Ramtin Mojtahedi Saffari and Sattar Mirzakuchaki has explained image encryption based on discrete wavelet transformation and Haar transformation [9]. In this algorithm, two dimensional logistic map is used to generate private key. In Latin square and chaotic map based image encryption scheme, cellular neural network is used to generate chaotic sequence [10].