在虚拟光学数据加密理论模型的基础上,提出了一种光学图像加密的可视化密码构造算法。该加密算法基于自由空间传播的光学系统,利用级联迭代角谱相位恢复算法把待加密图像分别编码到两块相位模板之中,从而实现图像的加密。该加密技术不但可通过同时调整两块相位模板的相位分布的搜索策略来扩大搜索空间,提高安全强度,而且扩大了系统密钥空间,使系统获得更高的安全性,且能通过简单的数值运算或光学实验装置得到质量非常高的解密图像,还从理论上分析了该算法的时间复杂度。计算机模拟结果表明,该加密算法的收敛速度快,能迅速找到非常好的近似解,解密图像质量高且系统安全性良好。

A new technique of optical image encryption and decryption based on the methodology of virtual optics is proposed. The technique is based on the free space propagation optical system and encodes the target image into two different phase masks (PM) by using cascaded iterative angular spectrum phase retrieval approach (CIASA) and both two phase masks can serve as enciphered texts. The proposed algorithm employs an improved scheme, i.e. modifying the phase distributions of two phase masks synchronously and enlarging the search space, and the time complexity of the algorithm is discussed, too. Computer simulations show that the algorithm generates much faster convergence and better image quality for the decrypted image and key space enlarged. These characters may introduce high security-level that makes the encrypted image much harder to be decrypted by an unauthorized person.