Intelligent Reflecting Surface-Assisted Secret Key Generation with Discrete Phase Shifts in Static Environment

Physical layer secret key generation is a promising candidate to achieve one-time-pad encryption approach for the wirelesscommunication system. However, in a static environment, the secret key rate is low due to the lack of channel time-variation.To solve this problem, this paper proposes a novel secret key generation scheme assisted by an intelligent reflecting surfacewith discrete phase shifts. In the scheme, legitimate nodes construct the dynamic time-varying channel by rapidly and randomlyswitching the phase of IRS elements. Then, channel coefficients are used to generate the secret key. Based on the IRS channelmodel, we derive the probability distribution of the channel coefficient and the expressions of the secret key rate. Furthermore,we optimize the secret key rate by adjusting the switching time of the IRS phase. Monte Carlo simulation and numerical resultsshow that our proposed scheme can update the secret key in a static environment.