Color image encryption algorithm based on bidirectional spiral transformation and DNA coding

The security of digital images has become increasingly important as information technology has advanced considerably. To ensure image security and improve the efficiency of image encryption, a novel color image encryption algorithm is proposed in this paper. Firstly, a novel three-dimensional chaotic system with extreme multistability is proposed and employed to generate the chaotic sequences to be used in the permutation and diffusion processes. Secondly, the proposed bidirectional spiral transformation is used to permute the R, G and B components extracted from the color plain image. Thirdly, the permuted pixel sequence is dynamically encoded into a DNA sequence. To further increase the permutation effect, the DNA sequence is permuted again using the index sequence. Finally, the dynamical DNA operations are performed to diffuse the permuted DNA sequence, and the designed look-up table method is used to quickly obtain the DNA operation results. The key space of the proposed algorithm is 10(266), which is large enough to resist the brute-force attacks. The average entropy value of the cipher image of Peppers is 7.9971, which is much closer to the theoretical entropy value 8. The dynamic DNA operations process only takes up 0.032349s, which shows the advantage of the proposed look-up table method. Therefore, the proposed algorithm can be applied to the application that require high confidentiality and real-time.