This paper investigates a physical layer key generation (PLKG) scheme for reconfigurable intelligent surface (RIS)-aided millimeter-wave (mmWave) multiple-input multipleoutput (MIMO) systems. Unlike traditional PLKG which relies on channel state information (CSI), we exploit the virtual angles of departure (AoDs). To accurately estimate these angles, we propose a redundant transforming matrix-based compressive sampling matching pursuit (RTMCoSa) method. We then derive the secret key rate (SKR) of the RIS-aided mmWave system. Simulation results demonstrate that the RTMCoSa method outperforms existing orthogonal matching pursuit (OMP) methods in channel probing for angle information. What is more, the proposed key generation scheme surpasses traditional CSI-based methods in SKR when the SNR is low. And the SKR of our method maintains robust when the SNR decreases.
This paper investigates a physical layer key generation (PLKG) scheme for reconfigurable intelligent surface (RIS)-aided millimeter-wave (mmWave) multiple-input multipleoutput (MIMO) systems. Unlike traditional PLKG which relies on channel state information (CSI), we exploit the virtual angles of departure (AoDs). To accurately estimate these angles, we propose a redundant transforming matrix-based compressive sampling matching pursuit (RTMCoSa) method. We then derive the secret key rate (SKR) of the RIS-aided mmWave system. Simulation results demonstrate that the RTMCoSa method outperforms existing orthogonal matching pursuit (OMP) methods in channel probing for angle information. What is more, the proposed key generation scheme surpasses traditional CSI-based methods in SKR when the SNR is low. And the SKR of our method maintains robust when the SNR decreases.
Secret key generation in physical layer security exploits the unpredictable random nature of wireless channels. The millimeter-wave (mmWave) channels have limited multipath and channel randomness in static environments. In this paper, for mmWave secret key generation of physical layer security, we use a reconfigurable intelligent surface (RIS) to induce randomness directly in wireless environments, without adding complexity to transceivers. We consider RIS to have continuous individual phase shifts (CIPS) and derive the RIS-assisted reflection channel distribution with its parameters. Then, we propose continuous group phase shifts (CGPS) to increase the randomness specifically at legal parties. Since the continuous phase shifts are expensive to implement, we analyze discrete individual phase shifts (DIPS) and derive the corresponding channel distribution, which is dependent on the quantization bit. We then derive the secret key rate (SKR) to evaluate the randomness performance. With the simulation results verifying the analytical results, this work explains the mathematical principles and lays a foundation for future mmWave evaluation and optimization of artificial channel randomness.
Recently, there is a growing interest in employing reconfigurable intelligent surface (RIS) to assist physical layer key generation in wireless networks. However, current works only studied the RIS-aided key generation schemes in SISO (single-input-single-output) communications, which have relatively low key generation rate (KGR). Therefore, here, in order to fill this gap, we propose the new and really novel RIS-aided MIMO (multiple-input-multiple-output) key generation scheme. By fully exploring the reflection signals from the RIS to the legitimate communication partners as the introduced, controllable and artificial randomness, combined with the spatial degree-of-freedom of RIS and MIMO incident and reflected signals, the KGR performance can be significantly improved. The information theoretical security is fully investigated, and the upper bound value of KGR is derived to comprehensively evaluate the system performance. The simulations fully validate the effectiveness and robustness of the proposed new and really novel, and interesting scheme.
Recently, there has been a growing interest in utilizing reconfigurable intelligent surfaces (RIS) for physical layer key generation (PLKG) due to their ability to intelligently configure the wireless medium. However, to the best of our knowledge, no study has explored the potential of active RIS (ARIS) in aiding PLKG. Motivated by this gap, this letter investigates the application of ARIS in PLKG. Furthermore, most existing RIS-aided PLKG techniques are based on the idealistic assumption of independent and identically distributed (i.i.d.) fading model at the RIS. Accordingly, we further consider the intrinsic correlated fading among the RIS elements. We derive the secret key rate (SKR) of the ARIS-aided PLKG and propose a sequential convex approximation (SCA) based optimization method to jointly optimize the phase and gain of the ARIS to reach maximum SKR. Additionally, we compare the performance of passive RIS (PRIS) aided PLKG with ARIS-aided PLKG. We show that with an equal total power budget, ARIS leads to significantly higher SKR, thereby offering promisingly high energy efficiency (EE) compared to PRIS.
Physical Layer Key Generation (PLKG) provides a promising approach for establishing secure cryptographic keys between legitimate parties. However, in static and quasi-static environments, the key generation rate is significantly limited due to the low entropy of the wireless channel. To overcome this, Reconfigurable Intelligent Surfaces (RIS) have been proposed to enhance the channel entropy by altering the phase of incident electromagnetic waves. This paper addresses this challenge by proposing a security architecture that integrates a Multi-Input Multi-Output (MIMO) base station with a Beyond-Diagonal Reconfigurable Intelligent Surface (BD-RIS) in multi-user scenarios, in the presence of an eavesdropper. Unlike conventional RIS, BD-RIS not only modifies the phase but also the magnitude of the impinging signals, introducing an additional degree of freedom that further enhances channel randomness. The secret key capacity of the proposed system is compared with that of conventional RIS in two scenarios: firstly, when a direct link exists alongside the BD-RIS-assisted link. Secondly, when the direct link is completely obstructed by an obstacle. Simulation results demonstrate that the proposed BD-RIS architecture outperforms conventional diagonal RIS (D-RIS) in all scenarios. Furthermore, the generated keys undergo randomness tests, successfully passing all National Institute of Standards and Technology (NIST) randomness subtests as well as the Autocorrelation (AC) test, confirming their suitability for secure communications. These findings establish BD-RIS as a promising technology for enhancing physical layer security in static environments for 5G/6G networks and IoT applications.
Physical layer key generation (PLKG) is a promising method to generate secret keys by harnessing the randomness of wireless channels. In this letter, a reconfigurable intelligent surface (RIS)-assisted multi-carrier PLKG framework is proposed to overcome the lack of channel randomness in static environments. Specifically, the secret key generation rate (SKGR) is analyzed based on the inter-frequency correlation among the channel coefficients across subcarriers. Building upon this analysis, a novel scheme for configuring RIS elements is proposed to enhance the SKGR by introducing correlations into the random phase shifts of RIS elements. Simulation results are presented to validate the effectiveness of the proposed scheme.
Shared secret key generation from wireless channel characteristics has attracted a lot of research attention in recent years due to its low computational overhead and potentials to achieve information-theoretic security. In this paper, for millimeter wave (mmWave) Massive MIMO channel, we propose to use new channel characteristics - virtual AoA (Angle of Arrival) and AoD (Angle of Departure), to generate a shared secret key between two devices. Other than reciprocity, AoA and AoD of the virtual channel present sparsity and their estimation is efficient and robust against noise. Through theoretical analysis and extensive simulations, we show that the proposed key generation using virtual AoA and AoD achieves much higher bit agreement ratio than existing mechanisms directly using channel state information. Our method can achieve above 99% bit agreement ratio even under very low SNR (e.g., -10dB), which is not achievable by the existing mechanisms. Besides, in our proposed mechanism, the bit agreement ratio becomes higher when number of antennas increases, along with higher key generate rates achieved per channel sounding.