| Chaos produces a random-like wideband signal sensitive to initial conditions. When a chaotic signal is used as a “carrier” to send a message, the message is not only carried, but also “masked” by the carrier. The message may be recovered perfectly at a receiver that is synchronized with the transmitter by using the received signal. This method, called chaotic encryption, is an alternative way for secure communication.; Some cracking methods, however, have been designed to show that such a communication may not be secure enough if the transmitter carrier is generated by simple forms of chaos. One way for improving the security of chaotic encryption is to construct a chaotic system which generates more complicated signals. Another way is to design chaotic synchronization approaches to increase the randomness of the carrier even if the carrier is from a less complicated chaotic system.; A chaotic synchronization approach is designed. Here, two identical chaotic systems can be synchronized by long interval impulsive chaotic signals. The recovered message is error-free even though a little large noise is added into the systems. The security of the communication is much higher than that using continuous chaotic signals because the randomness of the carrier is greatly increased and it is very difficult to reconstruct an attractor from the carrier.; A generalized competitive mode (GCM) approach is developed. The idea of the approach is that chaos is the result of a form of mode competition. The necessary condition for a system to be chaotic is that there are at least two such GCM's in the system. By using the necessary condition, the chaotic parameter regimes in several chaotic systems are estimated. Further, it is found that the number and the form of GCM's will affect the complexity of chaos. Therefore, one can construct new chaotic systems with pre-designed GCM's. Several new chaotic systems are created. Some iii of them produce very complex chaotic motions. The nonlinear dynamical forecasting (NDF) technique, perhaps the most complicated and powerful cracking method, is employed to show that the security of the communication via these systems is much improved compared to some well-known chaotic systems. Thus, the work may make it possible to develop devices for reasonably secure and practical communication in industry. (Abstract shortened by UMI.)... |
