Random Beam Switching: A Physical Layer Key Generation Approach to Safeguard mmWave Electronic Devices

Extracting secret keys from millimeter wave (mmWave) wireless channels fast and efficiently for securing communications between mmWave electronic devices is a challenge due to the limitations of static environments. In this paper, we propose a random beam switching (RBS) based physical layer key generation (PLKG) scheme in the mmWave systems. Utilizing the sparsity characteristics of mmWave channels between electronic devices, we apply virtual angles of effective-beams and activated-beams as the random source. Through channel detection, we establish an RBS space between the transmitter and receiver. Then they randomly select beams from the RBS space and transmit reference signals to generate consistent keys. Furthermore, by using information theory, we analyze the effectiveness, reliability and security performance of RBS scheme theoretically. Specifically, we derive the theoretical expression of key generation rate (KGR) and then obtain its upper bound. We also prove that the key mismatch ratio (KMR) approaches zero in the high signal-to-noise ratio (SNR) region. Then we demonstrate that the eavesdropper cannot obtain any information about the activated-beams. Numerical results are provided to verify our theoretical analysis. We demonstrate that the RBS scheme can provide sufficient secret keys even in static environments while achieving good secrecy performance to safeguard electronic devices.