In this paper, we investigate how an illegitimate user can use a reconfigurable intelligent surface (RIS) to maximally degrade the secrecy performance of the legitimate system. We first consider the case when the illegitimate user performs eavesdropping only. A problem is formulated to minimize the system secrecy rate by optimizing the phase shifts of the RIS elements. We also consider the case when the illegitimate user works with full-duplex technology and can perform eavesdropping and jamming simultaneously through the RIS. A problem is formulated to minimize the system secrecy rate by optimizing the jamming power and the phase shifts of the RIS elements. Although the two formulated problems are nonconvex, they are optimally solved in this paper. Our results show that good eavesdropping performance can be achieved by placing the RIS at an appropriate position. Further, jamming plus eavesdropping can largely reduce the secrecy rate of the legitimate system.

翻译：本文研究了非法用户如何利用可重构智能表面（RIS）最大限度地降低合法系统的保密性能。首先考虑非法用户仅执行窃听的情形，通过优化RIS单元的相位偏移构建最小化系统保密速率的问题。同时考虑非法用户采用全双工技术，通过RIS同时实现窃听与干扰的情形，通过优化干扰功率与RIS单元相位偏移构建最小化系统保密速率的问题。尽管所构建的两个问题均为非凸优化，但本文给出了其最优解。结果表明，将RIS部署在适当位置可获得良好的窃听性能，且干扰与窃听的联合作用能大幅降低合法系统的保密速率。