  In order to meet the demands of future innovative applications, many efforts
have been made to exceed the limits predicted by Shannon's Theory. Besides the
investigation of beyond-Shannon metrics such as security, latency, and
semantics, another direction is to jointly design the transceiver and the
environment by utilizing the intelligent reflecting surface (IRS). In this
paper, we consider the analysis and design of IRS-aided multiple-input
multiple-output (MIMO) secure communications, which has attracted much research
attention but still in its infancy. For example, despite their importance, the
fundamental limits of IRS-aided wiretap MIMO communications are not yet
available in the literature. In this paper, we will investigate these
fundamental limits by determining the ergodic secrecy rate (ESR) and secrecy
outage probability (SOP). For that purpose, the central limit theorem (CLT) for
the joint distributions of the mutual information (MI) statistics over the
IRS-aided MIMO secure communication channel is derived by utilizing the random
matrix theory (RMT). The derived CLT is then used to obtain the closed form
expressions for the ESR and SOP, which are also extended to the scenario with
multiple multi-antenna eavesdroppers. Based on the theoretical results,
algorithms for maximizing the artificial noise (AN) aided ESR and minimizing
the SOP are proposed. Numerical results validate the accuracy of the
theoretical results and effectiveness of the proposed optimization algorithms.
