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A Novel Color Image Encryption Scheme Based on Permutation-substitution Architecture

A novel color image encryption scheme with permutation-substitution architecture is proposed. One round of permutation and one round of substitution achieve desirable results. The color plain-image sized H W  is converted to 2D matrix with size 3 H W  and then divided into two equal parts 1, 2 P P . The 2D skew tent map is applied to generate pseudo-random sequences for the permutation and substitution processes implemented row-by-row/column-by-column instead of pixel-by-pixel to increase the encryption rate. The permutation is performed between 1, 2 P P and the substitution is executed within the permuted image. The security and performance of the proposed scheme have been analyzed as well. All the experimental results show that the proposed scheme is secure and effective for practical application. Introduction Thanks to the fantastic features of chaotic systems, such as high sensitivity to initial conditions and control parameters, ergodicity, pseudo-randomness etc., chaos-based image encryption schemes are extensively studied and developed recently. On one hand, traditional encryption algorithms, such as DES, AES, are typically designed for textual information and are not suitable for image encryption due to the intrinsic natures of images like high redundancy and high correlation among pixels [1]. On the other hand, the good chaotic natures agree with the fundamental requirements such as confusion and diffusion in cryptography, and therefore chaotic systems provide a potential candidate for constructing cryptosystems [2-4]. Since Fridrich firstly presented the fundamental permutation-diffusion architecture of chaos-based image encryption in 1998, a great number of chaos-based image encryption algorithms with such permutation-diffusion architecture have been proposed [2-6]. However Wang et al. found that the typical permutation-diffusion architecture with fixed parameters has one fatal drawback, that is, the two processes will become independent if the plain-image is a homogeneous one with identical pixel gray value [7]. As a matter of fact, some image encryption algorithms with permutation-diffusion architecture have been broken by chosen-plaintext or known-plaintext attacks [8,9]. In this paper, we present an image encryption scheme with permutation-substitution mechanism instead of permutation-diffusion mechanism. Permutation-substitution mechanism has been shown to be one effective mechanism for constructing ciphers [6]. The image encryption scheme proposed here consists of two stages: one permutation and one substitution. They are performed between the , , R G B components of color image. The color plain-image sized H W  is converted to a 2D matrix with size 3 H W  and then is divided into two parts