Controllable Asymmetry Attack on Two-Way Fiber Time Synchronization System

Precise and secure time synchronization between two remote sites is necessary in many practical scenarios. Recently, the two-way fiber time transfer (TWFTT) system has become an attractive option for high-precision time synchronization. However, TWFTT is implemented based on symmetric link assumption, and such assumption may be maliciously utilized to cause significant time asynchronization to TWFTT. In this paper, we propose two novel controllable asymmetry attack schemes for TWFTT, namely, the link asymmetry attack and the attenuation asymmetry attack. We theoretically analyze the controllability and the effectiveness of these two attacks. Experimental results show that our link asymmetry attack can introduce 2.49 ns time offset per asymmetric link length (in meters), and our attenuation asymmetry attack can introduce at most 36.6 times time offset (compared to normal situation) when the attenuation is 45.3%. Our work can provide instructive insights for future studies of protecting TWFTT from delay asymmetry attacks.