  The appearance of sixth-generation networks has resulted in the proposal of
several solutions to tackle signal loss. One of these solutions is the
utilization of reconfigurable intelligent surfaces (RIS), which can reflect or
refract signals as required. This integration offers significant potential to
improve the coverage area from the sender to the receiver. In this paper, we
present a comprehensive framework for analyzing the secrecy performance of a
RIS-aided mixed radio frequency (RF)-free space optics (FSO) system, for the
first time. Our study assumes that a secure message is transmitted from a RF
transmitter to a FSO receiver through an intermediate relay. The RF link
experiences Rician fading while the FSO link experiences M\'alaga distributed
turbulence with pointing errors. We examine three scenarios: 1) RF-link
eavesdropping, 2) FSO-link eavesdropping, and 3) a simultaneous eavesdropping
attack on both RF and FSO links. We evaluate the secrecy performance using
analytical expressions to compute secrecy metrics such as the average secrecy
capacity, secrecy outage probability, strictly positive secrecy capacity,
effective secrecy throughput, and intercept probability. Our results are
confirmed via Monte-Carlo simulations and demonstrate that fading parameters,
atmospheric turbulence conditions, pointing errors, and detection techniques
play a crucial role in enhancing secrecy performance.
