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Selective Combinational Encryption of Gray Scale Images using Orthogonal Polynomials based Transformation


R. Krishnamoorthi, P. D. Sheba Kezia Malarchelvi


Vol. 8  No. 5  pp. 195-204


In this paper, we propose a new image encryption technique in orthogonal polynomials based transformation domain (OPT) with selective combinational scrambling for secure transmission of images. Normally, the values of the neighboring pixels are highly correlated in most of the images. In order to de-correlate the intelligible information present in the image we propose the use of orthogonal polynomials based transformation. Also, the proposed technique exploits the energy preserving property of the orthogonal polynomials based transform coding which compacts energy in a few low frequency coefficients. These low frequency coefficients are selected as candidates for encryption which significantly reduces the number of bits to be encrypted. Then shuffling of these coefficients and their bits are performed. In addition, the sign bits of the selected low frequency coefficients are encrypted and randomly selected transformed blocks are shuffled. A symmetric key based cryptographically secure pseudo random process controls the entire encryption process. Experimental results reveal that the proposed OPT domain encryption scheme provides very low encryption PSNRs implying effective encryption. Also, security analyses prove that the proposed technique is robust to brute force, statistical and differential attacks.


Image encryption, Orthogonal Polynomials, Selective combinational Scrambling