A nonlinear multi-image encryption scheme is proposed by combining the reality-preserving discrete fractional angular transform with the deoxyribonucleic acid sequence operations. Four approximation coefficients of the four images are extracted by performing the two-dimensional lifting wavelet transform. Then, the four approximation coefficients are synthesized to generate a real-valued output with the reality-preserving discrete fractional angular transform. Finally, based on the deoxyribonucleic acid operation and the Logistic-sine system, the real-valued intermedium output will be encrypted to yield the final ciphertext image. To enhance the security of the image encryption algorithm, the initial value of the chaotic system is calculated by the 256-bit binary sequence, which is obtained by taking the statistics information of the plaintext images as the input of SHA-256. Deoxyribonucleic acid sequence operations, as nonlinear processes, could help to improve the robustness of the cryptosystem. Simulation results and security analysis demonstrate the effectiveness of the image encryption algorithm and the capability of withstanding various common attacks.

中文翻译：

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具有保留真实性的离散分数角变换和 DNA 序列的非线性多图像加密方案

通过将保留现实的离散分数角变换与脱氧核糖核酸序列操作相结合，提出了一种非线性多图像加密方案。通过执行二维提升小波变换，提取四幅图像的四个近似系数。然后，四个近似系数被合成以生成具有现实保留离散分数角变换的实值输出。最后，基于脱氧核糖核酸操作和Logistic-sine系统，对实值中间输出进行加密，得到最终的密文图像。为增强图像加密算法的安全性，混沌系统的初始值由256位二进制序列计算，将明文图片的统计信息作为SHA-256的输入得到。脱氧核糖核酸序列操作作为非线性过程，有助于提高密码系统的鲁棒性。仿真结果和安全分析证明了图像加密算法的有效性和抵御各种常见攻击的能力。