Cryptography with Dynamical Systems

Dynamical systems are often described as \unpredictable" or \com-plex" as aspects of their behavior may bear a cryptic relationship with the simple evolution laws which deene them. Some theorists work to quantify this complexity in various ways. Others try to turn the cryptic nature of dynamical systems to a practical end: encryption of messages to preserve their secrecy. Here some previous eeorts to engineer cryptosystems based on dynamical systems are reviewed, leading up to a detailed proposal for a cellular automaton cryptosystem. Cryptosystems constructed from cellular automaton primitives can be implemented in simply constructed massively parallel hardware. They can be counted on to deliver high encryption/decryption rates at low cost. In addition to these practical features, cellular automaton cryptosystems may help illuminate some foundational issues in both dynamical systems theory and cryptology, since each of these disciplines rests heavily on the meanings given to the intuitive notion of complexity.