Improved fractal coding and hyperchaotic system for lossless image compression and encryption

In response to the growing demand for computation and storage, and increasing vulnerabilities to attacks, maintaining image security and integrity remains a critical challenge. This paper introduces a novel, lossless image compression algorithm integrating improved fractal coding and a robust encryption method based on a new hyperchaotic system, irregular block permutation, and non-adjacent diffusion. The proposed 4D hyperchaotic system exhibits a wider chaotic range and more complex dynamics than existing systems, generating high-quality pseudo-random sequences for enhanced encryption security. Additionally, a lossless multi-directional delta encoding and segment run-length encoding method, utilizing variable-grid fractal coding, are developed to optimize data compression and preserve information integrity. Furthermore, a Tetris-based permutation and 2D nonlinear diffusion technique is proposed, using irregular patterns and non-adjacent double diffusion to resist various attacks. Experiments show that compared with other compression and encryption algorithms, the proposed algorithm has a higher compression ratio, strong sensitivity to key or plaintext, and can resist various attacks, such as brute-force attacks, statistical attacks and differentiable attacks.