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.

中文翻译：

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双向光纤时间同步系统的可控不对称攻击


在许多实际场景中，两个远程站点之间精确、安全的时间同步是必要的。近年来，双向光纤时间传递（TWFTT）系统已成为高精度时间同步的一个有吸引力的选择。然而，TWFTT是基于对称链路假设来实现的，并且这种假设可能被恶意利用而导致与TWFTT的显着时间不同步。在本文中，我们提出了两种新颖的TWFTT可控不对称攻击方案，即链路不对称攻击和衰减不对称攻击。我们从理论上分析了这两种攻击的可控性和有效性。实验结果表明，我们的链路不对称攻击可以在每个不对称链路长度（以米为单位）引入2.49 ns的时间偏移，而当衰减为45.3%时，我们的衰减不对称攻击最多可以引入36.6倍的时间偏移（与正常情况相比）。我们的工作可以为未来保护 TWFTT 免受延迟不对称攻击的研究提供指导性见解。