Secure multilevel permutation-diffusion based image encryption using chaotic and hyper-chaotic maps

This paper proposes a technique that encrypt images using chaotic and hyper-chaotic maps. To attain a high level of security and to get a better encryption effect, the proposed technique performs multilevel permutation and diffusion operations such as block, pixel, and bit-level to encrypt images. In this technique, block-level permutation operation is first performed using Alpar’s map followed by Arnold cat map based pixel-level permutations. Finally, in the permutation stage, hyper-chaotic map based bit-level shuffling operation is performed for over strengthening of the encryption system. To make the ciphertext totally independent of the plaintext, the proposed scheme performs all the three levels of diffusion operations such as bit, pixel, and block-level. In the diffusion stage, Piece-wise Linear Chaotic Map (PWLCM) based bit-level diffusion operation is first performed followed by pixel-level diffusion operation. Finally, block-level diffusion operation is performed to get encryption output. In each of the levels of encryption operation, a hash value (256-bits) of plaintext is used to strongly resist the algorithm against known-plaintext attack and chosen-plaintext attack. The security analyses and computer simulations indicate the good encryption outputs, higher key space and gray scale uniformity, stronger resistance of entropy, differential, and statistical attacks as well as fewer computations to perform encryption operation. This proves the strong ability of the proposed scheme to encrypt gray scale images.