A Color Image Encryption Scheme Based on a Four-Dimensional Discrete Chaotic System with Dynamic Channel Permutation and Bidirectional Cross-Diffusion

Color image encryption must simultaneously suppress spatial redundancy, adjacent-pixel correlation, and inter-channel dependence. However, many existing schemes based on independent RGB processing, simple cross-channel permutation, and unidirectional diffusion still provide limited spatial–channel collaborative mixing. To address this issue, this paper proposes a color image encryption scheme driven by a four-dimensional discrete chaotic system. The proposed design integrates a four-dimensional chaotic source with sinusoidal modulation and feedback coupling, plaintext-related global scrambling with 24-mode dynamic channel mixing, and bidirectional cross-diffusion within a unified collaborative framework. In this framework, the chaotic system provides complex control sequences, the scrambling and channel-mixing stages jointly reorganize pixel positions and RGB relationships, and the bidirectional diffusion stage strengthens perturbation propagation across both spatial positions and color channels. Dynamical analyses, NIST SP800-22 tests, and the 0–1 test verify the complexity and randomness of the chaotic source, with all median [Formula: see text] values higher than 0.998. Experimental results show that the average ciphertext entropy, NPCR, and UACI reach 7.999, 99.655%, and 33.442%, respectively. These results indicate that the proposed collaborative framework achieves effective statistical concealment, differential sensitivity, and spatial–channel decorrelation without excessive structural complexity.