一种相位截断傅里叶变换非对称光学压缩加密系统

A Phase-truncated Fourier Transform Asymmetric Optical Compression and Encryption System

基本相位截断傅里叶变换系统面对两步傅里叶迭代等攻击算法时,防御能力差极易被攻破,且加密时间长,密文密钥体积大,不便于分发与传输。提出将压缩感知与相位截断傅里叶变换光学非对称加密相结合,明文经离散小波变换分为低频信息和高频信息,利用压缩感知对高频信息压缩2/3,将其转化为低频信息的相位信息,共同构造大小为原明文图像1/4的待加密复图像。在第一块相位调制模板后增加一块振幅模板,采用设定阈值振幅截断方式,将部分振幅信息作为新私钥,相位角作为密文,实现加解密密钥完全不同,且一图一密。系统安全性能实验、攻击实验和对比实验表明,该加密系统可有效抵御各种攻击,鲁棒性高、传输量小、加密耗时短、解密图像重构质量好,整体性能优良。

Symmetric encryption is a classic encryption method.The algorithm is relatively mature.The encryption and decryption keys are the same key.The decryption method of the algorithm is basically the inverse operation of the encryption algorithm.Although the calculation speed is fast and the complexity is low,the encryption system is linear.Features also bring great hidden dangers to the security of the system.Classical optical encryption systems are mostly symmetrical encryption methods.The asymmetric encryption method distinguishes the encryption key and decryption key of the system,encrypts the information with the public key,and only the corresponding private key information can complete the correct decryption.This encryption method that divides the key into key pairs is not only suitable for actual key information distribution and management,but also destroys the linear characteristics of the encryption system,and the encryption system is more secure.The asymmetric cryptosystem based on Phase-truncated Fourier Transforms(PTFT)uses phase truncation to obtain the decryption key in the encryption process,breaking the linear operation of the algorithm.The separation of the encryption key and the decryption key is realized,and the security of the system has been greatly improved.Although the PTFT system hides the phase information in the encryption system by intercepting the phase and constructs an asymmetric encryption system;but under the condition of satisfying the"Kerckhoffs assumption",the deciphering of the asymmetric encryption system with phase interception only takes two steps to iterate the Fourier transform algorithm to recover the private key information of the system.The security of the encryption system is insufficient.From the cracking algorithm of the system,we can see that the complex value information of the system is divided into phase and amplitude,so that the encrypted values are all amplitude information;the cracking of the system takes advantage of this feature.In this paper,an undisclosed amplitude template is added after the first phase modulation template,and the threshold amplitude truncation method is adopted.Part of the amplitude information is used as the new private key,and the phase angle is used as the ciphertext.The conditions are broken and the security of the encryption system is enhanced.Although the security of the improved system is guaranteed,in addition to a set of ciphertext information,two sets of intercepted phase information need to be transmitted during information transmission,and the amount of information transmission is tripled.This encryption method brings huge compression to the transmission and storage of information,especially for large-capacity information transmission,the efficiency of information transmission is reduced.In order to achieve the data compression of the transmitted information,this paper proposes to combine compressed sensing with PTFT optical asymmetric encryption.The plaintext is divided into low-frequency information and high-frequency information by discrete wavelet transform.The high-frequency information is compressed by 2/3 by using compressed sensing.It is transformed into phase information of low-frequency information,and jointly constructs a complex image to be encrypted whose size is 1/4 of the original plaintext image.System security performance experiments,attack experiments and comparative experiments show that the encryption system in this paper can effectively resist various attacks,has high robustness,small transmission volume,short encryption time,good quality of decrypted image reconstruction,and excellent overall performance.