  In this paper, we study resource allocation design for secure communication
in intelligent reflecting surface (IRS)-assisted multiuser multiple-input
single-output (MISO) communication systems. To enhance physical layer security,
artificial noise (AN) is transmitted from the base station (BS) to deliberately
impair the channel of an eavesdropper. In particular, we jointly optimize the
phase shift matrix at the IRS and the beamforming vectors and AN covariance
matrix at the BS for maximization of the system sum secrecy rate. To handle the
resulting non-convex optimization problem, we develop an efficient suboptimal
algorithm based on alternating optimization, successive convex approximation,
semidefinite relaxation, and manifold optimization. Our simulation results
reveal that the proposed scheme substantially improves the system sum secrecy
rate compared to two baseline schemes.
