  This paper investigates the problem of increasing the security at the
physical layer of a Millimeter Wave (mmWave) network equipped with several
Intelligent Reflecting Surfaces (IRSs). In this network, multiple IRSs help the
Base Station (BS) to reach the signal to the desired user and at the same time
maintain the security of the network i.e. securing the signal from receiving by
the unallowable eavesdropper. The target of the proposed scheme is to maximize
the secrecy rate by jointly optimizing the active beamforming at the BS and
passive beamforming at the IRSs. This leads to a non-convex optimization
problem which we solve by decomposing into two sub-problems. The sub-problems
alternatively solve the active and passive beamforming design problems using
the Semi-Definite Relaxation (SDR) technique. Finally, simulations are done to
assess the performance of the proposed algorithm. These results show the
superiority of using multiple IRSs in the enhancement of the secrecy rate in
the wireless networks that operate in the mmWave frequency bands.
