  Reconfigurable intelligent surface (RIS) has been regarded as a promising
technology since it has ability to create the favorable channel conditions.
This paper investigates the secure communications of RIS assisted
non-orthogonal multiple access (NOMA) networks, where both external and
internal eavesdropping scenarios are taken into consideration. More
specifically, novel approximate and asymptotic expressions of secrecy outage
probability (SOP) for the k-th legitimate user (LU) are derived by invoking
imperfect successive interference cancellation (ipSIC) and perfect successive
interference cancellation (pSIC). To characterize the secrecy performance of
RIS-NOMA networks, the diversity order of the k-th LU with ipSIC/pSIC is
obtained in the high signal-to-noise ratio region. The secrecy system
throughput of RIS-NOMA networks is discussed in delay-limited transmission
mode. Numerical results are presented to verify theoretical analysis that: i)
The SOP of RIS-NOMA networks is superior to that of RIS assisted orthogonal
multiple access (OMA) and conventional cooperative communication schemes; ii)
As the number of reflecting elements increases, the RIS-NOMA networks are
capable of achieving the enhanced secrecy performance; and iii) The RIS-NOMA
networks have better secrecy system throughput than that of RIS-OMA networks
and conventional cooperative communication schemes.
