Chaos-based image encryption has become a prominent area of research in recent years. In comparison to ordinary chaotic systems, fractional-order chaotic systems tend to have a greater number of control parameters and more complex dynamical characteristics. Thus, an increasing number of researchers are introducing fractional-order chaotic systems to enhance the security of chaos-based image encryption. However, their suggested algorithms still suffer from some security, practicality, and efficiency problems. To address these problems, we first constructed a new fractional-order 3D Lorenz chaotic system and a 2D sinusoidally constrained polynomial hyper-chaotic map (2D-SCPM). Then, we elaborately developed a multi-image encryption algorithm based on the new fractional-order 3D Lorenz chaotic system and 2D-SCPM (MIEA-FCSM). The introduction of the fractional-order 3D Lorenz chaotic system with the fourth parameter not only enables MIEA-FCSM to have a significantly large key space but also enhances its overall security. Compared with recent alternatives, the structure of 2D-SCPM is simpler and more conducive to application implementation. In our proposed MIEA-FCSM, multi-channel fusion initially reduces the number of pixels to one-sixth of the original. Next, after two rounds of plaintext-related chaotic random substitution, dynamic diffusion, and fast scrambling, the fused 2D pixel matrix is eventually encrypted into the ciphertext one. According to numerous experiments and analyses, MIEA-FCSM obtained excellent scores for key space ($2^{541}$), correlation coefficients (<0.004), information entropy (7.9994), NPCR (99.6098%), and UACI (33.4659%). Significantly, MIEA-FCSM also attained an average encryption rate as high as 168.5608 Mbps. Due to the superiority of the new fractional-order chaotic system, 2D-SCPM, and targeted designs, MIEA-FCSM outperforms many recently reported leading image encryption algorithms.

Aiming at the problem of insufficient security of image encryption technology, a secure image encryption algorithm using chaos-based block permutation and weighted bit planes chain diffusion is proposed, which is based on a variant structure of classical permutation-diffusion. During the permutation phase, the encryption operations of dividing an image into sub-block, block scrambling, block rotation and block inversion, negative-positive transformation, color component shuffling are performed sequentially with chaotic sequences of plaintext association. In the chain diffusion stage, different encryption strategies are adopted for the high and low 4-bit planes according to the weight of image information. Theoretical analyses and empirical results substantiate that the algorithm conforms to the cryptographic requirements of confusion, diffusion, and avalanche effects, while possessing excellent numerical statistical properties with a large cryptographic space. Therefore, the cryptanalysis-propelled security enhancement mechanism proposed in this paper effectively amplifies the aptitude of the algorithm to withstand cryptographic attacks.