Hardware-Impaired PHY Secret Key Generation With Man-in-the-Middle Adversaries

In this letter, we examine the PHY layer secret key generation (PHY-SKG) scheme in the presence of man-in-the-middle (MiM) adversary, while legitimate parties suffer from hardware impairments (HIs). Different from previous works on PHY-SKG that consider adversaries who simply try to make an interference in the communication link, the MiM aims to deceive legitimate entities about the source of common randomness. To conquer the MiM attack, legitimate parties utilize randomized pilots (RPs) in our proposed scheme. We analyze the effect of HIs on the performance of system by deriving the achievable secret key rate (SKR). Our results highlight a fundamental limit, as a ceiling phenomena, on the SKR when having practical imperfections. Top-level guidelines for selecting impairment levels along the transceiver chains is also provided to maximize the performance of the PHY-SKG protocol. Our numerical results verify the analytic expressions derived, while providing insights on system design. We show that by properly considering the HIs, about 25% improvement in the SKR is achievable.