Analyses and New Designs of Digital Chaotic Ciphers
SJ Li · Surrey Research Insight Open Access (The University of Surrey) · 2003
=©A) Since 1980s, the idea of using digital chaotic systems to design new ciphers has attractedmore andmore attention. The use of chaos in cryptography depends on the natural relation between the two research areas: strong dynamical properties of chaotic systems implies strong cryptographical properties of cryptosystems, and the basic way to make cryptosystems have good strong cryptographical properties implies quasi-chaos (we even can find the phantom of chaos in Shanon’s classic paper on theory of secrecy systems). Basically speaking, there are two paradigms of applying chaos for secure applications: analog chaotic secure communications (mainly based on chaos synchronization technique) and digital chaotic ciphers realized in computers. This dissertation only focuses on digital chaotic ciphers, i.e., the area lying between chaos theory and pure cryptography in finite-state (digital) world. The first boom of research on digital chaotic ciphers occurred near 1990, but decayed rapidly after some negative works on the security of proposed ciphers. The research boom returned in late 1990s, andmuchmore contributions are made to get many promising achievements. Although a number of recently-proposed digital chaotic ciphers have been cryptanalyzed, many others have not been effectively attacked. Also, some general ways to digital chaotic ciphers have been proposed and more careful considerations are made to ensure their security, such as the chaotic block ciphers based on fixed or dynamic S-boxes. However, as an important issue in the design of digital chaotic ciphers, dynamical degradation of digital chaotic systems has not been seriously considered by most designers of digital chaotic ciphers. One task of this dissertation is to emphasize significance of this issue and to give some initial investigations. Our contributions in this dissertation involve the following three aspects about digital chaotic ciphers: theoretical analyses of dynamical degradation of digital chaotic systems, cryptanalyses of digital chaotic ciphers, and new proposals of digital chaotic ciphers. The main achievements contained in this disserta-