Symbol-Block Ciphering With CBC Mode for Secure Digital Coherent Optical Communication

In recent years, the growing demand for security in optical fiber communications, driven by the development of high-capacity communications based on digital coherent transmission technology, has necessitated advanced physical-layer security measures. This study focuses on symbol block ciphering techniques, evaluating the security performance of applying the cipher block chaining (CBC) mode with a 2-bit key. Specifically, dual-polarized-16 quadrature amplitude modulation signals were encrypted using CBC mode, and the signal quality during transmission over 2240 km of standard single-mode fiber was examined through numerical analysis and experiments. The results demonstrated that CBC mode enables proper signal recovery even in transmission paths affected by nonlinear effects, albeit with slight performance penalties regarding optical signal to noise ratio and transmission distance. Furthermore, by comparing the reception accuracy of an eavesdropper without the encryption key, the study highlighted the potential of CBC mode to provide enhanced security.