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IEEE Wireless Communications Letters

Enhancing Physical-Layer Secret Key Generation Through Random Antenna Positioning

Toshiki Matsumine, Hideki Ochiai, Junji Shikata

Published Jan 1, 2026• 0 citations
Publisher

Abstract

Physical-layer secret key generation enables information-theoretic security by extracting secret keys from channel reciprocity. A key challenge, however, is the limited secret-key rate (SKR) in slow-fading environments. To address this, we propose a movable antenna–aided scheme in which the legitimate parties independently randomize their antenna positions at each probe, inducing channel variation even when the underlying channel parameters are fixed. We show that, with a sufficiently large movement region and many propagation paths, the resulting channel effectively emulates a Gaussian model even in a static setting. Simulations further demonstrate substantial gains in SKR outage performance, with outage probability decreasing as the number of channel probes increases.

DOI
10.1109/lwc.2026.3693289

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Physical-layer secret key generation enables information-theoretic security by extracting secret keys from channel reciprocity. A key challenge, however, is the limited secret-key rate (SKR) in slow-fading environments. To address this, we propose a movable antenna–aided scheme in which the legitimate parties independently randomize their antenna positions at each probe, inducing channel variation even when the underlying channel parameters are fixed. We show that, with a sufficiently large movement region and many propagation paths, the resulting channel effectively emulates a Gaussian model even in a static setting. Simulations further demonstrate substantial gains in SKR outage performance, with outage probability decreasing as the number of channel probes increases.
Wireless key generation in slow fading channels is challenging because of the limited channel variation and randomness. This paper proposes a novel artificial randomness (AR) assisted approach for fast key generation in slow fading environments. It integrates user-designed randomness into the channel probing to form a fast-changing combined channel to realize information-theory security. The analytical expressions of secret key capacity are derived. We find that it is possible to improve secret key capacity by introducing AR when legitimate users have a better channel condition than that of eavesdropper. We also find that the improved secret key capacity is proportional to the channel probing number and is bounded by the noise variance and channel condition. Simulation and experimental results show that AR approach can generate secret key effectively in slow fading environments by carefully designing probing numbers. Compared to existing work in literature, the proposed approach does not rely on multiple antennas or extra helpers, and it can be applied in both single antenna and multi-antenna systems.
Physical layer secret key generation exploits the reciprocal channel randomness for key generation and has proven to be an effective addition security layer in wireless communications. However, static or scarcely random channels require artificially induced dynamics to improve the secrecy performance, e.g., using intelligent reflecting surface (IRS). One key challenge is that the induced random phase from IRS is also reflected in the direction to eavesdroppers (Eve). This leakage enables Eve nodes to estimate the legitimate channels and secret key via a globally known pilot sequence. To mitigate the secret key leakage issue, we propose to exploit random matrix theory to inform the design of a new physical layer secret key generation (PL-SKG) algorithm. We prove that, when sending appropriate random Gaussian matrices, the singular values of Alice's and Bob's received signals follow a similar probability distribution. Leveraging these common singular values, we propose a random Gaussian matrix based PL-SKG (RGM PL-SKG), which avoids the usages of the globally known pilot and thereby prevents the aforementioned leakage issue. Our results show the following: (i) high noise resistance which leads to superior secret key rate (SKR) improvement (up to 300%) in low SNR regime, and (ii) general improved SKR performance against multiple colluded Eves. We believe our combination of random matrix theory and PL-SKG shows a new paradigm to secure the wireless communication channels.
This paper presents a random pilot full-duplex (FD) secret key generation scheme designed to enhance security in static wireless environments. In these environments, where inherent channel randomness is limited, efficiently extracting secret keys poses a significant challenge. The proposed scheme leverages the benefits of both FD operation and random pilot transmission to overcome this limitation and enhance the physical layer security. In this scheme, one of the FD nodes transmits random pilot signals, unknown to the eavesdropper, during the channel probing phase to artificially increase the shared randomness between the legitimate communicating nodes. By considering correlated eavesdropping, we derive the lower and upper bounds for the achievable secret key rate (SKR). The results reveal that the proposed FD scheme outperforms the HD scheme even in the presence of residual SI. Furthermore, the secret key rate can be improved by better SIC channel estimation and lower eavesdropper channel correlation.
Physical-layer secret key generation has emerged as a promising solution for establishing cryptographic keys by leveraging reciprocal and time-varying wireless channels. However, existing approaches suffer from low key generation rates and vulnerabilities under various attacks in slowly varying environments. We propose a new physical-layer secret key generation approach with channel obfuscation, which improves the dynamic property of channel parameters based on random filtering and random antenna scheduling. Our approach makes one party obfuscate the channel to allow the legitimate party to obtain similar dynamic channel parameters, yet prevents a third party from inferring the obfuscation information. Our approach allows more random bits to be extracted from the obfuscated channel parameters by a joint design of the K-L transform and adaptive quantization. Results from a testbed implementation show that our approach, compared to the existing ones that we evaluate, performs the best in generating high entropy bits at a fast rate and is able to resist various attacks in slowly varying environments. Specifically, our approach can achieve a significantly faster secret bit generation rate at roughly 67 bit/pkt, and the key sequences can pass the randomness tests of the NIST test suite.
This paper investigates physical-layer key generation (PLKG) in multi-antenna base station systems, by leveraging a fluid antenna system (FAS) to dynamically customize radio environments. Without requiring additional nodes or extensive radio frequency (RF) chains, the FAS effectively enables adaptive antenna port selection by exploiting channel spatial correlation to enhance the secret key rate (SKR) at legitimate nodes. To comprehensively evaluate the performance of the FAS in PLKG, we propose an FAS-assisted PLKG model that integrates transmit beamforming and sparse port selection under independent and identically distributed (i.i.d.) and spatially correlated channel models, respectively. Specifically, the PLKG utilizes reciprocal channel probing to derive an approximate SKR expression based on the mutual information between legitimate channel estimates, explicitly accounting for the Eve’s channel observation under spatially correlated channel scenarios. Nonconvex optimization problems for these scenarios are formulated to maximize the SKR subject to transmit power constraints and sparse port activation. We propose an iterative algorithm by capitalizing on successive convex approximation and Cauchy-Schwarz inequality to obtain a locally optimal solution. A reweighted ℓ1-norm-based algorithm is applied to advocate for the sparse port activation of FAS-assisted PLKG. To approximate the optimal activated ports obtained by exhaustive search, a low-complexity sliding window-based port selection is proposed to substitute reweighted ℓ1-norm method based on Rayleigh-quotient analysis. Simulation results demonstrate that the FAS-assisted PLKG scheme significantly outperforms fixed antenna-assisted PLKG schemes in both environments. It is shown that the FAS achieves higher SKR with fewer RF chains through dynamic sparse port selection, which effectively reduces the resource overhead. Also, the sliding window approach closely approximates the globally optimal port selection compared to the reweighted ℓ1-norm method, rendering it suitable for practical deployments.
This paper presents a novel physical-layer approach to information security. Unlike conventional mathematical-based encryptors, a secret key is generated from a natural phenomenon, i.e., the multi-path fading of a radio wave. The reciprocity in wave propagation is exploited to share the key with a party on the air. An array of electronically steered parasitic radiators provides time variation in the faded amplitude. This variation exhibits strong spatio-randomness which can never be practically solved by any other party. We show proof-of-concept experiments carried out in an actual indoor environment.