The Analysis Of Security Of The 4f Optical Encryption System

The weakness of information security is increasing as the remarkable development of computer technology. For this reason, the investigation of the security of image encryption technology has been widespread concerned. Many researchers dedicated to searchs for the methods of image encryption and have made notable progress. Some encryption techniques have emerged, among which the double random phase encryption system has been widely used in the optical information security technology. Because of the reason that the plaintext and the ciphertext satisfy the Object-image relation in this system, this encryption system is a linear system essentially and there are weakness of the security.Most of the researchs about optical encryption system are restricted in the cryptography. Until 2005, Carnicer et al presented a"Chosen ciphertext attack"to cracked the double random phase encryption system, soon after, Peng et al cracked this system by"Known- plaintext Attacks based on phase retrieval algorithm". At the same time, Gopinathan et al described"Known plaintext heuristic attack"on the Fourier plane encryption algorithm. But many of these attacks require a large quantity of information, and will result errors to the decrypted result. For instance, the"Chosen ciphertext attack"requires a access to a large number of chosen ciphertext. For this reason we have to explore a new method which needs less information and bring little errors.In this paper, we comment on theoretical basis of information security and cryptography and introduce the double random phase encryption development at home and abroad, in particular we present the work as follows:(1). We overview several optical encryption methods and simulate these methods mainly including: double random phase encryption, fresnel encryption and fractional fourier.(2). As the technology of phase retrieval is the key technology of the attacks, we investigate and compare several of the phase retrieval alogrithms in the 3th chapter to chose a better algorithms, and discussed the factors that affect the convergence.(3). The security of the optical encryption system is discussed. Then we comment on several possible attacks on the DRP encryption scheme and the known plaintext attacks is simulated based on the phase retrieval algorithm. And the only ciphertext is also discussed.