Study On Cryptanalysis Of Optical And Symmetric Encryption System

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.