Chaotic Encryption Algorithm Using Dynamic Permutation and Nonlinear Substitution Techniques for Color and Grayscale Images

This paper presents a capable hyper-chaos-based image encryption algorithm using an enhanced Henon map. The bifurcation diagrams, Lyapunov exponents, and NIST test ensure the dynamic behavior and hyperchaotic performance of the enhanced Henon and its suitability for image encryption. The proposed method follows a confusion–diffusion or substitution–permutation strategy using hyperchaotic keystreams with novel techniques. The hyperchaotic keystreams are generated from an enhanced Henon map, whose control parameters and initial values are calculated from an image-independent 512-bit encryption key. The encryption phase includes image-dependent permutation-substitution techniques; here, the permutation stage utilizes variant Hilbert curves, and the substitution phase uses nonlinear composite modulo additive-XOR operations, and both are employed by jointly considering the hash value of the image and the chaotic keystream. Here, the hash value, encapsulating the input-specific traits, and the random chaotic key sequences generated from the enhanced hyperchaotic Henon map make unique encryption possible for each image, even with the same encryption key. Finally, the modified hash values through the hyperchaotic keystream are randomly inserted into the encrypted image to produce the final cipher image. Our method guarantees better statistical, differential, and entropy values for encrypted images, resilience against various attacks, a vast keyspace, and superior time efficiency in comparison with some currently proposed methods.