A Novel Secure Key Stream Generator Based on Chaotic Multistate Cellular Automata

The security and reliability requirements for communication systems are increasingly stringent due to the exponential growth in demand for information exchange. Key stream generators are critical components of secure communication systems. However, chaotic-based key stream generators are susceptible to inherent dynamic degradation phenomena, which pose significant security risks. To address this vulnerability, this article proposes a novel key stream generator based on a chaotic multistate cellular automaton (CA). We develop a chaotic 8-state CA using a 2-D logistic tent modular map to generate both the chaotic rule space and cellular space. The state data of the CA can be updated in parallel, and each state can be directly used as a key stream through simple binary conversion. Furthermore, the Lyapunov exponent theoretical calculation method is extended to multistate CA, thereby verifying the chaotic behavior of the proposed 8-state CA. Finally, the obtained results show that the proposed key stream generator is not affected by dynamic degradation, and can achieve a maximum expandable key space of $8^{2^{27}}$ . The generator successfully passes the NIST and TestU01 standard random number tests. This study provides a novel framework for designing key stream generators and demonstrates the potential application of multistate CA in secure communication.