  In this paper, a reconfigurable intelligent surface (RIS)-aided underlay
cognitive radio network is investigated. An RIS is utilized to improve the
secondary network (SN) reliability and robustness while simultaneously
increasing the physical layer security of the primary network (PN). Toward this
end, closedform expressions for the SN outage probability, PN secrecy outage
probability, and PN probability of non-zero secrecy capacity are derived. To
increase the eavesdropping signals of the PN, the eavesdropper uses two
combining techniques, namely maximal ratio combining and selection combining.
Furthermore, the advantages of the proposed system model are verified through
numerical and simulation results.
