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.
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.
In this work, we present a scheme of physical layer secret key generation for Millimeter wave (mmWave) Massive MIMO system. Our scheme is compatible with current hardware structure and protocols including Analog Beamforming, Massive MIMO, and Beam Sweep. We add a small perturbation angle into the Angle of Arrival (AoA) of the transmitter as the common randomness, which significantly improved the secret key rate without being constrained by the complexity of link initialization protocols and low dynamic of the channel. Therefore, the secret key rate can be enhanced by increasing the number of perturbations. In addition, our scheme can combat co-located eavesdropper (Eve) by utilizing the high directionality of Massive MIMO antenna. Numerical results show that our scheme has a high bit agreement ratio (BAR) between legitimate users while the co-located Eve only gets the BAR around 50%, which indicates that the secrecy of the generated key is well achieved.
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.
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.
The unpredictability of the wireless channel has been used as a natural source of randomness to build physical-layer security primitives for shared key generation, authentication, access control, proximity verification, and other security properties. Compared to pseudo-random generators, it has the potential to achieve information-theoretic security. In sub-6 GHz frequencies, the randomness is harvested from the small-scale fading effects of RF signal propagation in rich scattering environments. However, the RF propagation characteristics follow sparse models with clustered paths when devices operate in millimeter-wave (mmWave) bands (5G and Next-Generation networks, Wi-Fi in 60GHz). Millimeter-wave transmissions are typically directional to increase the gain and combat high signal attenuation, leading to stable and more predictable channels. In this paper, we first demonstrate that state-of-the-art methods relying on channel state information or received signal strength measurements fail to produce high randomness. Accounting for the unique features of mmWave propagation, we propose a novel randomness extraction mechanism that exploits the random timing of channel blockage to harvest random bits. Compared with the prior art in CSI-based and context-based randomness extraction, our protocol remains secure againstpassive and active Man-in-the-Middle adversaries co-located with the legitimate devices. We demonstrate the security properties of our method in a 28 GHz mmWave testbed in an indoor setting.
Millimeter wave (mmWave) communication encounters a major issue of extremely high power consumption. To address this problem, the simultaneous wireless information and power transfer (SWIPT) could be a promising technology. The mmWave frequencies are more appropriate for the SWIPT comparing to current low-frequency wireless transmissions, since mmWave base stations (BSs) can pack with large antenna arrays to achieve significant array gains and high-speed short-distance transmissions. Unfortunately, the implementation of SWIPT in the wireless communication may lead to an expanded defencelessness against the eavesdropping due to high transmission power and data spillage. It is conventionally believed that narrow beam offers inherent information-theoretic security against the eavesdropping, because only the eavesdroppers, which rely on the line-of-sight path between the legitimate transmitter and receiver, can receive strong enough signals. However, some mmWave experiments have shown that even by using highly directional mmWaves, the reflection signals caused by objects in the environment can be beneficial to the eavesdroppers. This paper studies the security performance in general mmWave SWIPT networks, and investigates the probability of successful eavesdropping under different attack models. Analytical expressions of eavesdropping success probability (ESP) of both independent and colluding eavesdroppers are derived by incorporating the random reflection paths in the environment. Theoretical analysis and simulation results reveal the effects of some key parameters on the ESP, such as the time switching strategy in SWIPT, densities of mmWave BSs, and carriers frequencies, etc. Based on the numerical and simulation results, some design suggestions of mmWave SWIPT are provided to defend against eavesdropping attacks and achieve secure communication in practice.
Physical layer key generation (PLKG) has emerged as a promising strategy for securing wireless communication using shared channel knowledge between two legitimate users. Traditional PLKG systems rely on time-frequency domain channels using metrics such as Received Signal Strength Indicator (RSSI) or Channel State Information (CSI) to generate secure keys. As a result of the rapid variation in the time-frequency domain channels, these systems are prone to error and suffer from a high reconciliation overhead requirement. Conversely, the same channels have a sparse and static representation in the delay-Doppler domain, which is utilized by the recently introduced Orthogonal Time Frequency Space (OTFS) modulation scheme. Furthermore, the channel representation in the delay-Doppler domain is uniquely determined by the scattering environment between the transmitter-receiver pair. In this paper, we leverage the sparsity of the delay-Doppler domain channel as well as the uniqueness of the channel representation to introduce two OTFS based PLKG schemes. We show through extensive simulations that the introduced OTFS schemes can get < 10% bit disagreement ratio (BDR) in scenarios where time-frequency domain based RSSI methods break down.