  This paper investigates physical layer security (PLS) in the intelligent
reflecting surface (IRS)-assisted multiple-user uplink channel. Since the
instantaneous eavesdropper's channel state information (CSI) is unavailable,
the secrecy rate can not be measured. In this case, existing investigations
usually focus on the maximization of the minimum (max-min) of signal to
interference plus noise power ratio (SINRs) among multiple users, and do not
consider secrecy outage probability caused by eavesdroppers. In this paper, we
first formulate the minimization of the maximum (min-max) secrecy outage
probability among multiple users. The formulated problem is solved by
alternately optimizing receiving matrix and phase shift matrix. Simulations
demonstrate that the maximum secrecy outage probability is significantly
reduced with the proposed algorithm compared to max-min SINR strategies,
meaning our scheme has a higher security performance.
