  We investigate transmission optimization for intelligent reflecting surface
(IRS) assisted multi-antenna systems from the physical-layer security
perspective. The design goal is to maximize the system secrecy rate subject to
the source transmit power constraint and the unit modulus constraints imposed
on phase shifts at the IRS. To solve this complicated non-convex problem, we
develop an efficient alternating algorithm where the solutions to the transmit
covariance of the source and the phase shift matrix of the IRS are achieved in
closed form and semi-closed forms, respectively. The convergence of the
proposed algorithm is guaranteed theoretically. Simulations results validate
the performance advantage of the proposed optimized design.
