The Analysis Of Security Of The Asymmetric Cryptosystem Based On Phase-truncated Fourier Transforms

Optical image encryption is a new encryption technology in recent years. Since Javidi et al proposed a representative double random phase encryption system,many kinds of encryption systems have been proposed, but there are problems of linear and key distribution in these encryption systems. Peng proposed an asymmetric encryption system based on phase-truncated Fourier transforms. Due to the asymmetric and nonlinear nature, the encryption system is better than the typical symmetric optical encryption system.In this dissertation, we first analyze some typical optical encryption systems,and point out the limitations of these encryption systems and the necessity of developing non symmetric optical encryption systems.Then we discuss the asymmetric optical encryption system based on phase-truncated Fourier transforms and analyzed the safety problem of the system,pointed out the ability of resist known-plaintext attack and chosen-plaintext attack.After according to Yang-Gu recovery algorithms, we proposed a scheme of Ciphertext- Only attack the system. Through the known ciphertext and public key information to recover plaintext. The results of numerical simulation shows the feasibility of the scheme, but also illustrates the encryption system has security issues.Considering the attack is not ideal in the results, this paper analyses and studies phase recovery algorithm from the angle of mathematics, puts forward a scheme of optimize Yang-Gu algorithm based on random phase perturbation. And we use it to attack the asymmetric encryption system. In the start of attack process,the iteration isn’t soon stalled, but continue iterative recovery. This makes the attack effect was greatly improved, and the result of numerical simulation illustrate the effectiveness of the scheme.