  This letter investigates the secure communication in a reconfigurable
intelligent surface (RIS)-aided multiuser massive multiple-input
multiple-output (MIMO) system exploiting artificial noise (AN). We first derive
a closed-form expression of the ergodic secrecy rate under spatially correlated
MIMO channels. By using this derived result, we further optimize the power
fraction of AN in closed form and the RIS phase shifts by developing a
gradient-based algorithm, which requires only statistical channel state
information (CSI). Our analysis shows that spatial correlation at the RIS
provides an additional dimension for optimizing the RIS phase shifts. Numerical
simulations validate the analytical results which show the insightful interplay
among the system parameters and the degradation of secrecy performance due to
high spatial correlation at the RIS.
