Analysis, Improvement And Applications For Several Chaotic Cryptography Systems

With the rapid development and extensive applications of computer and communication technologies, digital information is being applied more and more widely in the world. Digital information is easy to copy and distribute, this also produces many security problems in its applications. As a result, the security and protection of digital information are becoming increasingly a key problem that must be solved urgently. It's well known that cryptography is the fundamental method for information security.There is natural relationship between chaos and cryptography: strong dynamical properties of chaotic system imply strong cryptographical properties, and the basic way to design strong cryptosystem implies quasi-chaos. Since 1980s, the idea of using chaotic systems to design new ciphers has attracted more and more attention. Recently, much more contributions are made to get many promising achievements. At the same time, some systematic ways to design chaotic ciphers have been proposed with careful considerations on the security of algorithms.This dissertation focuses on the analysis and design of chaotic cryptosystems. The main achievements and originality contained in this dissertation are as follows:(1) The research status and advances of chaotic ciphers has been summarized, analyzed and reviewed. The analyzing method of chaotic block cipher has been expatiated in detail, and several existent key problems to be solved urgently have been pointed out.(2) We successful attack the chaotic cryptosystem based on discretized skew tent map proposed by Masuda et al. A chosen plaintext attack requiring only two plaintexts is proposed. The test results demonstrate that this encryption cryptosystem is easily broken under the proposed chosen plaintext attack. An improved cryptosystem is proposed with key expansion, which is more secure and scalable than previous version.(3) Security analysis of an enhanced Baptista-type cryptosystem proposed by S. Li et al is carried out in detail. We show that this cryptosystem still leak partial information on the current chaotic state and reduce the secure of cryptosystem. Furthermore, the chosen plaintext attack has successfully been applied to attack to this cryptosystem..(4) Based on the high-dimension matrix transformation, a fast public key...