Reconfigurable intelligent surface (RIS) and ambient backscatter communication (AmBC) have been envisioned as two promising technologies due to their high transmission reliability as well as energy-efficiency. This paper investigates the secrecy performance of RIS assisted AmBC networks. New closed-form and asymptotic expressions of secrecy outage probability for RIS-AmBC networks are derived by taking into account both imperfect successive interference cancellation (ipSIC) and perfect SIC (pSIC) cases. On top of these, the secrecy diversity order of legitimate user is obtained in high signal-to-noise ratio region, which equals \emph{zero} and is proportional to the number of RIS elements for ipSIC and pSIC, respectively. The secrecy throughput and energy efficiency are further surveyed to evaluate the secure effectiveness of RIS-AmBC networks. Numerical results are provided to verify the accuracy of theoretical analyses and manifest that: i) The secrecy outage behavior of RIS-AmBC networks exceeds that of conventional AmBC networks; ii) Due to the mutual interference between direct and backscattering links, the number of RIS elements has an optimal value to minimise the secrecy system outage probability; and iii) Secrecy throughput and energy efficiency are strongly influenced by the reflecting coefficient and eavesdropper's wiretapping ability.

翻译：可重构智能表面（RIS）与环境反向散射通信（AmBC）因其高传输可靠性与高能效特性，被视作两种极具前景的技术。本文研究了RIS辅助AmBC网络的保密性能。针对非理想连续干扰消除（ipSIC）与理想连续干扰消除（pSIC）两种情况，推导了RIS-AmBC网络保密中断概率的新的闭式及渐近表达式。在此基础上，获得了合法用户在高信噪比区域的保密分集阶数：当采用ipSIC时该分集阶数为零，而当采用pSIC时该阶数与RIS单元数量成正比。为评估RIS-AmBC网络的安全有效性，进一步研究了保密吞吐量与能量效率。数值结果验证了理论分析的准确性，并表明：i) RIS-AmBC网络的保密中断性能优于传统AmBC网络；ii) 由于直连链路与反向散射链路间的相互干扰，存在使保密系统中断概率最小化的RIS单元最优数量；iii) 保密吞吐量与能量效率受到反射系数及窃听者窃听能力的显著影响。