  In this paper, we propose a novel encrypted data transmission scheme using an
intelligent reflecting surface (IRS) to generate secret keys in wireless
communication networks. We show that perfectly secure one-time pad (OTP)
communications can be established by using a simple random phase shifting of
the IRS elements. To maximize the secure transmission rate, we design an
optimal time slot allocation algorithm for the IRS secret key generation and
the encrypted data transmission phases. Moreover, a theoretical expression of
the key generation rate is derived based on Poisson point process (PPP) for the
practical scenario when eavesdroppers' channel state information (CSI) is
unavailable. Simulation results show that employing our IRS-based scheme can
significantly improve the encrypted data transmission performance for a
wide-range of wireless channel gains and system parameters.
