【作者】 位恒政；

【导师】 彭翔；

【作者基本信息】 天津大学 ， 测试计量技术及仪器， 2008， 博士

【摘要】 基于光学理论与方法的数据加密已经有十多年的历史,各种光学加密方法被相继提出。从密码学的观点来看,目前国际上报道的对光学数据加密系统的研究工作主要停留在密码编码学的范畴,很少有人对光学加密系统进行严格的安全性分析。密码学包括密码编码学和密码分析学两方面的内容。因此,对光学加密系统的密码分析学研究,无论是从光学信息安全理论体系的完整性,还是从实际应用来看都是及其重要的。作为国家自然科学基金项目(项目号:60472107)、广东省自然科学基金项目(项目号:04300862)、深圳市科技计划项目(项目号:200426)、中国科学院微系统与信息技术研究所开放课题基金项目的重要研究内容之一,本论文系统研究了光学加密系统的密码学特点及其密码学分析方法,着重分析了双随机相位编码及其衍生技术的安全性。论文主要工作包括以下几个方面:1)提出一种双随机相位加密系统的“已知明文攻击的方法”。利用该攻击方法,攻击者只需一个明文-密文对,通过常规的双强度相位恢复算法即可获得加密系统空域的随机相位函数密钥,继而轻易推导出频域的随机相位函数密钥,成功破解了这一国际著名的光学加密系统,并完成了该攻击算法的并行硬件实现。2)提出一种双随机相位加密系统的“选择明文攻击方法”。通过选择多个冲击函数作为明文,利用冲击函数的筛选性质,成功破解了基于数字方法实现的双随机相位加密系统,并给出了空域和频域密钥的解析式,此方法最大的优点在于解密图像的无损性。3)提出一种基于菲涅耳域的双随机相位加密系统的“选择明文攻击方法”。菲涅耳双随机相位加密系统相对于标准的4f双随机相位加密来说,增加了密钥的维数和变换的复杂性,但由于其仍是一个线性系统,因此其安全性不是很高。利用冲击函数的筛选性质,成功获得加密系统的密钥,并且此解密结果是无损的。4)提出一种“已知明文攻击的方法”,对基于POCS算法和4f相关器的密码系统进行了安全性分析。在此密码系统中,其解密结果以强度的形式输出,而不是复振幅的形式,而仅由强度输出信息不能轻易获得系统密钥。但由于其解密系统是一个典型的4f线性系统,因此基于POCS算法和4f相关器的安全系统也存在很大的安全隐患。该攻击方法将寻找系统密钥的过程转化为一个双强度相位恢复的问题,仅利用一个明文-密文对就获得了加密系统的密钥。更多还原

【Abstract】 Optical encryption technique has experienced the development more than ten years. Various kinds of optical encryption schemes have been proposed and implemented during the past decade. However, most of those approaches were focused on the coding schemes of optical cryptographic systems whereas a few involved in the cryptoanalysis. In terms of cryptology it consists of two research aspects: cryptography and cryptoanalysis. To this point, the security analysis of optical encryption systems is not only significant to the integrity of optical information security theory but also critical to the practical applications.This dissertation focused on the cryptoanalysis of currently developed optical encryption systems, in particular, on the cryptoanalysis to the double random phase encoding (DPRE) and its variation techniques. The research work is supported by Natural Science Foundation of China (Grant No. 60472107 ), Natural Science Foundation of Guangdong Province (Grant No. 031804), the Science & Technology Bureau of Shenzhen(Grant No. 200426), and Shanghai Institute of Microsystem and information Technology, Chinese Academy of Science. The major contributions in this dissertation are summarized as follows:1. A new approach for known-plaintext attack on DPRE is proposed. With this attack an opponent can obtain the phase keys in the input plane by typical phase retrieval algorithms and subsequently deduce the phase keys in the Fourier domain easily. Since the core calculations involved in the phase retrieval method is Fourier transform, it fits very well into the digital signal processor (DSP) architecture with which the processing speed will be greatly improved. The known-plaintext attack method implemented with high performance DSP is presented.2. A new approach for chosen-plaintext attack on optical encryption system based on DPRE is demonstrated. With this attack an opponent can access both random phase keys with the help of impulse functions. It is shown that analytical solutions of retrieved keys can be derived in a straightforward way. One of the most prominent advantages of proposed approach is that the decryption process is lossless. Numerical simulations for decryption show a good agreement with theoretical analysis. 3. A novel method for chosen-plaintext attack on lensless double-random phase encoding (L-DPRE) in the Fresnel domain is presented. Compared with DPRE encryption system, L-DPRE encryption system has lager keyspsace while still remains a linear system, so that security strength of this kind of cryptographic system is doubtful. An opponent would be likely to access two encryption keys with help of selecting the impulse functions as chosen plaintexts. One of the significant features of the proposed attack is that the decryption process is lossless.4. The security strength of the cryptosystem based on Projection-Onto -Constraint-Sets(POCS)algorithm and a 4f correlator is carefully examined. The known-plaintext attack based on phase retrieval algorithm is presented. In this specific cryptosystem only intensities can be measured at the output, it would not be easy to get the encryption keys. Nevertheless, the decryption of this cryptosystem can be equivalent to a standard 4f linear system. It is shown that the decryption process can be converted into a phase retrieval problem from two measured intensity information. An attacker is able to break down this cryptosystem with only input phase data and output intensity data. Numerical simulations are also presented to demonstrate the validity of proposed method.更多还原