Triple-image bit-level encryption algorithm based on double cross 2D hyperchaotic map

Derived from the Sine map and iterative chaotic map with infinite collapse (ICMIC), we design a new 2D hyperchaotic map called 2D-SIDCM (Sine ICMIC double cross map), which enhances the complexity of the chaotic system by mixing the different orbits of sub-systems. Based on the 2D-SIDCM, this paper proposes a novel triple-image bit-level encryption algorithm. Bit-level operation and scanning arrangements are introduced into the encryption. Bit-level scrambling is achieved by converting color images into combined bit-level grayscale matrices and randomly swapping binary numbers, while bit-level diffusion is performed by bit cyclic shifting and exclusive or (XOR). Scanning arrangements further reduce the correlation among adjacent pixels. To improve the ability of the algorithm against differential attacks, we adopt bidirectional diffusion including clockwise and anti-clockwise spiral diffusion. Besides, we perform selecting diffusion according to the quantized chaotic sequence, and the double pseudo-randomness greatly increases the security of the algorithm. Finally, three encrypted grayscale images are, respectively, placed on the R, G and B channels to synthesize a color cipher image. The corresponding channel of the ciphertext can be extracted to achieve selective decryption. Simulation results and security analysis indicate that our algorithm can encrypt three images simultaneously and has better security than several state-of-the-art encryption algorithms.