<p>In order to solve the problem of low security in image encryption algorithms based on a single chaotic map, this paper proposes a new chaotic system, namely, a cascaded modulated sine chaotic system (CMSCS) that can generate several different chaotic maps simultaneously. Based on this, we propose a block-based image encryption algorithm that leverages the characteristics of CMSCS to achieve one encryption at a time. Image encryption involves three stages. First, the CMSCS is constructed by introducing existing chaotic maps as seed maps, cascading them with nonlinear functions, and then performing a sine transform on them. The SHA-512 hash function is used to generate a key associated with the plaintext, which is then employed to produce a chaotic sequence with strong randomness. Next, a spiral scrambling algorithm is devised, which achieves pixel position swapping by rotating pixels clockwise and is combined with a chaotic-sequence-based scrambling algorithm to implement double scrambling of the plaintext. Finally, by integrating the two-dimensional index matrix position transformation method, we design a snake-shaped transform and a Latin square-like transform to achieve multiple nonlinear diffusion operations both within and between blocks. Simulation results show that the proposed encryption algorithm can effectively resist typical attacks such as brute-force attack, differential analysis, and statistical analysis, and exhibits high security.</p>