Applications Of Amplitude Modulation And Pixel Random Permutation Techniques In Double Random Phase Encryption System

With the rapid development of Internet and modern communication techniques, information security has been receiving more and more attention. Optical information processing, as a technique of non-mathematical cryptology, shows its great potential and plays an important role in the field of information security due to its inherent high parallel processing speed and large storage memories. Many proposals of encryption schemes arose in the past decade, among them, the most widely used and highly successful method is the double random phase encoding scheme proposed by Refregier and B. Javidi in 1995. However, the security of this very scheme has not been systematically analyzed until recently. A cryptographic algorithm can be claimed to be secure only if it is able to endure various attacks from cryptoanalysis. However, very few reports on this problem from the point of view of cryptoanalysis can be seen in the past. The double random phase encoding scheme adoptes the output plane (the image plane) of the 4f system as the ciphertext, thus, there is an object-image relationship between the plaintext and ciphertext. The encoding scheme is essentially a linear system. For a linear system, there is a simple function relationship between the plaintext, the ciphertext and the encoding keys. This means that there exsits a security flaw in the scheme. Recently, researchers systematically analyzed the resistance of the double random phase encoding scheme and pointed that it is susceptible to chosen and known plaintext attacks. Cryptoanalysis also indicates that the security worry originates from the linearity of the scheme.This thesis gives a systematic review of the developments of optical information security, also presents the security analysis of most-frequently used double random phase encoding scheme. Moreover, we propose several new encoding schemes that can highly enhance the security of conventional double random phase encoding scheme. Specifically, we have introduced two techniques (amplitude modulation and pixel random phase permutation techniques) which can break down the linearity of the scheme and then greatly enhance the security level of the system. The main initiative contributions in this thesis include following aspects:(1) A new approach of double random phase-amplitude encryption is proposed. It is achieved by introducing an amplitude modulator into the conventional double random phase encoding scheme. The use of the amplitude modulator as an additional hiding key can significantly enhance the security level of the system, and more importantly, it can remove the linearity of the scheme and thus ensure the resistance of the system against some attacks based on phase retrieval algorithm such as the known plaintext attack. A series of computer simulations have shown the effectiveness of this method and its resistance against known plaintext attack.(2) A new approach of double random phase encryption based on pixel random permutation technique is proposed. It is realized by imposing a pixel random permutation technique on the ciphertext of the conventional double random phase encoding scheme. This operation can be considered as a hiding key, and thus enhance the security level of the system. We have done a series of computer simulations which have shown the effectiveness of this method and its resistance against some attacks such as occlusion attack, noise attack and known plaintext attack.