This article studies novel attack and defense strategies, based on a class of stealthy attacks, namely the zero-dynamics attack (ZDA), for multiagent control systems. ZDA poses a formidable security challenge since its attack signal is hidden in the null space of the state-space representation of the control system and hence it can evade conventional detection methods. An intuitive defense strategy builds on changing the aforementioned representation via switching through a set of carefully crafted topologies. In this article, we propose realistic ZDA variations where the attacker is aware of this topology-switching strategy, and hence employs the following policies to avoid detection: first, pause, update, and resume ZDA according to the knowledge of switching topologies; and second, cooperate with a concurrent stealthy topology attack that alters network topology at switching times, such that the original ZDA is feasible under the corrupted topology. We first systematically study the proposed ZDA variations, and then develop defense strategies against them under the realistic assumption that the defender has no knowledge of attack starting, pausing, and resuming times and the number of misbehaving agents. Particularly, we characterize conditions for detectability of the proposed ZDA variations, in terms of the network topologies to be maintained, the set of agents to be monitored, and the measurements of the monitored agents that should be extracted, while simultaneously preserving the privacy of the states of the nonmonitored agents. We then propose an attack detection algorithm based on the Luenberger observer, using the characterized detectability conditions. We provide numerical simulation results to demonstrate our theoretical findings.

中文翻译：

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网络控制系统的新型隐形攻击和防御策略


本文研究了基于一类隐形攻击（即零动态攻击（ZDA））的多智能体控制系统的新型攻击和防御策略。 ZDA 提出了巨大的安全挑战，因为它的攻击信号隐藏在控制系统状态空间表示的零空间中，因此它可以逃避传统的检测方法。直观的防御策略建立在通过切换一组精心设计的拓扑来改变上述表示的基础上。在本文中，我们提出了现实的 ZDA 变体，其中攻击者知道这种拓扑切换策略，因此采用以下策略来避免检测：首先，根据切换拓扑的知识暂停、更新和恢复 ZDA；其次，配合并发隐形拓扑攻击，在切换时改变网络拓扑，使得原始 ZDA 在损坏的拓扑下是可行的。我们首先系统地研究所提出的 ZDA 变体，然后在防御者不知道攻击开始、暂停和恢复时间以及行为不当代理的数量的现实假设下制定针对它们的防御策略。特别是，我们根据要维护的网络拓扑、要监视的代理集以及应提取的受监视代理的测量来描述所提出的 ZDA 变化的可检测性条件，同时保护代理的隐私。非受监控代理的状态。然后，我们使用特征化的可检测性条件，提出一种基于 Luenberger 观察器的攻击检测算法。我们提供数值模拟结果来证明我们的理论发现。