  This letter investigates secure transmission in an intelligent reflecting
surface (IRS) assisted non-orthogonal multiple access (NOMA) network. Consider
a practical eavesdropping scenario with imperfect channel state information of
the eavesdropper, we propose a robust beamforming scheme using artificial noise
to guarantee secure NOMA transmission with the IRS. A joint transmit
beamforming and IRS phase shift optimization problem is formulated to minimize
the transmit power. Since the problem is non-convex and challenging to resolve,
we develop an effective alternative optimization (AO) algorithm to obtain
stationary point solutions. Simulation results validate the security advantage
of the robust beamforming scheme and the effectiveness of the AO algorithm.
