Abstract
Chaotic secure communication has several advantages over conventional crypto-based communication due to its simplicity, diversity and robustness. In this paper, we first present difference function projective synchronization (DFPS) for complex chaotic systems. It extends the category of synchronization and enables the development of applications based on complex chaotic signals instead of real signals, thereby increasing both the security and robustness for chaotic communications. We derive the control law using the active control theory based on Lyapunov stability analysis. A novel communication scheme is further designed based on DFPS. Its main idea is chaotic masking in essence, but the transmitted signal is the derivative of the sum of the information signal and chaotic signal. As the difference functions are complex and arbitrary, they are more unpredictable than real scaling functions, and the operations of complex numbers are complicated, thus greatly reducing the possibility that an interceptor extracts the information from the transmitted signal. The communication system can transmit both analog signal and digital symbols with fast transmission speed and high security, especially with low bit-error rate and strong robustness to noise for digital symbols. The main ideas of the proposed method are verified by the example of coupled complex Lorenz system used as both transmitter and receiver.