  This paper presents a quantified assessment of the physical layer security
capabilities of reconfigurable intelligent surface (RIS)-aided wireless systems
under eavesdropping. Specifically, we derive a closed-form expression for the
ergodic secrecy capacity (ESC) that is adaptable to different types of fading
and RIS size. The channels between the transmitter (TX) and RIS, the RIS and
legitimate receiver as well as the TX and eavesdropper are assumed to follow
independent mixture Gamma (MG) distributions. Note that MG is capable of
modeling a large variety of well-known distributions, including Gaussian,
Rayleigh, Nakagami-m, Rice, and others. The results reveal that as the RIS size
increases, although the legitimate links diversity order increases, the ESC
gain decreases.
