  Intelligent reflective surface (IRS) technology is emerging as a promising
performance enhancement technique for next-generation wireless networks. Hence,
we investigate the physical layer security of the downlink in IRS-aided
non-orthogonal multiple access networks in the presence of an eavesdropper,
where an IRS is deployed for enhancing the quality by assisting the cell-edge
user to communicate with the base station. To characterize the network's
performance, the expected value of the new channel statistics is derived for
the reflected links in the case of Nakagami-m fading. Furthermore, the
performance of the proposed network is evaluated both in terms of the secrecy
outage probability (SOP) and the average secrecy capacity (ASC). The
closed-form expressions of the SOP and the ASC are derived. We also study the
impact of various network parameters on the overall performance of the network
considered. To obtain further insights, the secrecy diversity orders and the
high signal-to-noise ratio slopes are obtained. We finally show that: 1) the
expectation of the channel gain in the reflected links is determined both by
the number of IRSs and by the Nakagami-m fading parameters; 2) The SOP of both
receiver 1 and receiver 2 becomes unity, when the number of IRSs is
sufficiently high; 3) The secrecy diversity orders are affected both by the
number of IRSs and by the Nakagami-m fading parameters, whereas the high-SNR
slopes are not affected by these parameters. Our Monte-Carlo simulations
perfectly demonstrate the analytical results.
