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IEEE Transactions on Vehicular Technology

Physical Layer Key Generation for IOS-Assisted Communication Systems

Guangchuan Cao, Yan Zhang, Zijie Ji, Mengyi Zhang, Yonghui Li

Published Jul 18, 2024• 2 citations
Publisher

Abstract

Different from reflecting-only metasurfaces, intelligent omni-surfaces (IOSs) are capable of both refracting and reflecting the received signals, providing a new technical solution to overcome coverage limitations. In this paper, we propose a physical layer secret key (PLSK) generation scheme in IOS-assisted communication systems for the first time. This scheme enhances the key generation rate (KGR) for legitimate users on both sides of the IOS. A selective optimization stage, based on proximal policy optimization (PPO) is designed to configure different refraction and reflection coefficients to improve secrecy performance. In addition, IOS random elements are allocated as artificial random sources to invoke variations of the legitimate channel, to weaken the capability of the eavesdropper to acquire the key. Simulation results demonstrate that the proposed scheme ensures the randomness of the PLSK while achieving a higher KGR than existing works under quasi-static conditions.

DOI
10.1109/tvt.2024.3430289

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Different from reflecting-only metasurfaces, intelligent omni-surfaces (IOSs) are capable of both refracting and reflecting the received signals, providing a new technical solution to overcome coverage limitations. In this paper, we propose a physical layer secret key (PLSK) generation scheme in IOS-assisted communication systems for the first time. This scheme enhances the key generation rate (KGR) for legitimate users on both sides of the IOS. A selective optimization stage, based on proximal policy optimization (PPO) is designed to configure different refraction and reflection coefficients to improve secrecy performance. In addition, IOS random elements are allocated as artificial random sources to invoke variations of the legitimate channel, to weaken the capability of the eavesdropper to acquire the key. Simulation results demonstrate that the proposed scheme ensures the randomness of the PLSK while achieving a higher KGR than existing works under quasi-static conditions.
In this paper, we propose a physical layer secret key (PLSK) generation scheme for secure encrypted transmissions in orbital angular momentum (OAM) communication systems which improves the secret key capacity via taking advantage of OAM orthogonal modes. Based on the line-of-sight (LoS) quasi-static channel conditions in OAM systems, we propose a mode-based active defense phase in the PLSK scheme to invalidate keys generated by an eavesdropper when it is extremely close to the legitimate user. Our simulation results highlight that the key information generated by the eavesdropper is almost zero in the case of highly correlated legitimate and eavesdropping channels under LoS conditions. In addition, our proposed OAM PLSK scheme achieves a higher key generation rate (KGR) than existing works since mode-based active defense can disrupt the process of PLSK by the eavesdropper.
Physical layer secret key generation (SKG) is a promising supplement for high-level encryption, which leverages the channel reciprocity and the natural randomness of wireless channel. However, practical implementations often exhibit static environment. To solve this problem, this paper proposes a novel secret key generation scheme assisted by an intelligent reflecting surface (IRS) which can smartly reconfigure the radio signal propagation to improve the secret key rate of SKG. Specially, we formulate the minimum achievable secret key capacity in the IRS-assisted multiple-input single-output (MISO) system with multiple eavesdroppers. Then, an optimization framework for designing IRS reflecting coefficients based on the secret key capacity lower bound is proposed. Numerical results show that our optimal IRS-assisted SKG scheme can achieve much higher achievable secret key capacity when compared with two benchmark schemes.
Physical layer secret key generation is a promising candidate to achieve one-time-pad encryption approach for the wireless communication 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 letter proposes a novel secret key generation scheme assisted by an intelligent reflecting surface with discrete phase shifts. In the scheme, legitimate nodes construct the dynamic time-varying channel by rapidly and randomly switching the phase of IRS elements. Then, channel coefficients are used to generate the secret key. Based on the IRS channel model, 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 results show that our proposed scheme can update the secret key in a static environment.
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.
In this paper, we propose an improved physical layer key generation scheme that can maximize the secret key capacity by deploying intelligent reflecting surface (IRS) near the legitimate user aiming at improving its signal-to-noise ratio (SNR). We consider the scenario of multiple input single output (MISO) against multiple relevant eavesdroppers. We elaborately design and optimize the reflection coefficient matrix of IRS elements that can improve the legitimate user's SNR through IRS passive beamforming and deteriorate the channel quality of eavesdroppers at the same time. We first derive the lower bound expression of the achievable key capacity, then solve the optimization problem based on semi-definite relaxation (SDR) and the convex-concave procedure (CCP) to maximize the secret key capacity. Simulation results show that our proposed scheme can significantly improve the secret key capacity and reduce hardware costs compared with other benchmark schemes.
Focusing on the issue of secret key generation for transportation systems and electronic devices in possible less-dynamic channel conditions, this paper proposes an intelligent reflective surface aided channel phase probing scheme (IRS-CPP) for improving physical layer key generation. Specifically, we consider the model that both legitimate nodes first acquire the secret key from the channel phase response by employing channel probing. Then, the passive IRS are utilized to enhance the probing signal by using random phase shifts, which can effectively modify the signal phases. Furthermore, we provide the performance analysis of the proposed scheme in terms of the theoretical key capacity to estimate performance of the scheme. Finally, comprehensive results including the key capacity, key generation rate (KGR), key inconsistency rate (KIR) and key randomness are investigated. Simulation results demonstrate that the proposed scheme can effectively enhance the physical layer key generation performance in the static scenario compared with the benchmark key generation schemes.