From the perspective of hard decision fusion, we investigate Byzantine attacks in Reconfigurable Intelligent Surface (RIS)-enhanced and decode-and-forward relay-assisted Cooperative Spectrum Sensing (CSS) for mobile Cognitive Radio Networks (CRNs) in this paper. Specially, a RIS-enhanced and decode-and-forward relay-assisted CSS configuration is first constructed under dynamic channel scenarios due to user mobility. Subsequently, the channel- and attack-aware hard decision fusion rules are developed, and the optimal channel-aware Byzantine attack strategies are then developed under both small-scale and large-scale attacking scenarios. The corresponding results depict that the optimal attack strategy does not require any a prior knowledge of the global instantaneous Channel State Information (ICSI) (e.g. false alarm probability and detection probability of all the secondary users), although perfect acquisition of ICSI is clearly always not affordable from the attacker perspective, which is further exacerbated by the RIS and decode-and-forward relays involved in CSS and the potential high mobility of secondary users that leads to fast fading channels. Furthermore, our counterintuitive results also indicate that, regardless of the attacker's awareness of the decision fusion rule, the optimal Byzantine attack can be achieved through a unifying framework, the explicit attack strategy may be not unique, and the attacking effectiveness is primarily determined by the fraction of the Byzantine nodes rather than the channel dynamics. That is, to make the channel-aware approach more practical, the challenge that the heavy reliance on the global ICSI and decision fusion rule in obtaining the Byzantine attacks is successfully relaxed. Finally, we empirically validate our theoretical analysis through extensive simulations across a wide range of attacking scenarios.

翻译：本文从硬决策融合的视角，研究了移动认知无线电网络中可重构智能表面增强与解码转发中继辅助的协作频谱感知系统面临的拜占庭攻击问题。具体而言，首先在用户移动性导致的动态信道场景下构建了RIS增强与解码转发中继辅助的CSS架构。随后，提出了信道与攻击感知的硬决策融合规则，并分别在小规模与大规模攻击场景下推导了最优的信道感知拜占庭攻击策略。结果表明：最优攻击策略无需任何全局瞬时信道状态信息的先验知识（例如所有次级用户的虚警概率与检测概率），尽管从攻击者视角完全获取ICSI显然不可行——这一困难因CSS中RIS与解码转发中继的引入以及次级用户潜在的高移动性导致的快衰落信道而进一步加剧。此外，我们反直觉的研究结论还表明：无论攻击者是否知晓决策融合规则，最优拜占庭攻击均可通过统一框架实现；显式攻击策略可能不唯一；攻击效果主要取决于拜占庭节点比例而非信道动态特性。这意味着，通过成功缓解传统方法对全局ICSI和决策融合规则的严重依赖，信道感知方案的实际可行性得以提升。最后，我们通过跨多种攻击场景的大规模仿真实验对理论分析进行了实证验证。