Cryptanalysis Of Several Digital Chaotic Cryptosystems

Chaotic cryptography is a cross discipline. In that cross discipline, chaos is applied into modern cryptography. Theoretically, continuous chaotic system has well randomness and sensitivity to initial conditions. Digital chaos system still has some good chaos properties such as good pseudo randomness, long-term unpredictability and high sensibility to the initial value and so on. These chaos properties are fit for some requirements of cryptography and there are some natural relationships between them. It inspires people to apply chaos theory into the field of cryptography. But chaos, after all, is not equal to cryptography. The integration and application of the two distinct disciplines also need research and exploration. Based on in-depth study on results of previous studies and digital chaotic cryptosystems, this paper makes a detailed analysis and improvement of several digital chaotic cryptosystems by numerical simulation method and theoretical analysis. The main points of this paper are as follows.This paper introduces the basic theory of chaos and the basic knowledge of cryptography, and then makes in-depth cryptanalysis on three kinds of previous digital chaotic cryptosystems. And in this foundation we present some improvements.Firstly, this paper makes an in-depth cryptanalysis on an ergodic chaotic encryption algorithm and then cracks the original algorithm by chosen plaintext attack with a specific example. On this basis, we give some advices to avoid the chosen plaintext attack and improve the encryption speed.Secondly, this paper makes a cryptanalysis of a chaos-based cryptosystem with adaptive arithmetic coder embedded, and then crack each part of the original algorithm respectively, and at last present some suggestions to improve the security of original algorithm.Lastly, based on a design of pseudo-random bit generator which based on single chaotic system, this paper proposed a new design with some performance analysis and random analysis. Theoretical analysis and numerical experiment show that the improved algorithm has good randomness, and it can meet the requirements of cryptography.