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IEEE International Conference on Distributed Computing Systems (ICDCS)

Physical Layer Secret Key Generation Leveraging Proactive Pilot Contamination

L. Liu, Hongbo Liu, Yicong Du, Ziyu Shao, Haomiao Yang, Yanzhi Ren

Published Jul 23, 2024• 2 citations
Publisher

Abstract

Physical layer-based secret key generation has garnered significant attention due to its inherent advantages of lightweight implementation, information-theoretic security, and broad applicability for mobile devices. The reciprocal randomness of the wireless channel ensures the consistent generation of secret bits between two communicating parties. However, it also suffers from the degradation of the efficiency of key generation attributed to the adverse impact of ambient noise, despite sustained efforts to mitigate the inconsistency during quantization. We find that a slight perturbation of the pilot signal, without affecting the correct reception of data frames, induces a corresponding change in the channel response, making it possibly adaptable to the target quantization strategies, thereby reducing the probability of key mismatch. Therefore, we take a different viewpoint on proactive contamination of the pilot signals to obtain the desired channel measurements for accurate physical layer secret key generation. Specifically, we design an adaptive pilot manipulation to avoid the expected channel measurements being too close to the quantization thresholds, enabling high quantization consistency. Furthermore, we also develop a random cross-threshold mechanism to prevent attackers from inferring the quantization results by monitoring the trend of pilot signal variations. A reliable long training sequence (LTS) modification mechanism is incorporated into our method to ensure communication performance by adaptively adjusting the scale of the pilot signal. To validate the effectiveness of our proposed method, we implement a prototype by re-configuring software modules in GNU radio running on the USRP platform. Extensive experiments demonstrate that our scheme outperforms existing representative quantization schemes with better key generation performance.

DOI
10.1109/icdcs60910.2024.00120

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Physical layer-based secret key generation has garnered significant attention due to its inherent advantages of lightweight implementation, information-theoretic security, and broad applicability for mobile devices. The reciprocal randomness of the wireless channel ensures the consistent generation of secret bits between two communicating parties. However, it also suffers from the degradation of the efficiency of key generation attributed to the adverse impact of ambient noise, despite sustained efforts to mitigate the inconsistency during quantization. We find that a slight perturbation of the pilot signal, without affecting the correct reception of data frames, induces a corresponding change in the channel response, making it possibly adaptable to the target quantization strategies, thereby reducing the probability of key mismatch. Therefore, we take a different viewpoint on proactive contamination of the pilot signals to obtain the desired channel measurements for accurate physical layer secret key generation. Specifically, we design an adaptive pilot manipulation to avoid the expected channel measurements being too close to the quantization thresholds, enabling high quantization consistency. Furthermore, we also develop a random cross-threshold mechanism to prevent attackers from inferring the quantization results by monitoring the trend of pilot signal variations. A reliable long training sequence (LTS) modification mechanism is incorporated into our method to ensure communication performance by adaptively adjusting the scale of the pilot signal. To validate the effectiveness of our proposed method, we implement a prototype by re-configuring software modules in GNU radio running on the USRP platform. Extensive experiments demonstrate that our scheme outperforms existing representative quantization schemes with better key generation performance.
Secret key generation plays an important role in device-to-device communication security in wireless networks. For consistent key generation between two communicating parties, existing matching-based key generation methods match segmented channel measurements (channel episodes) of similar patterns between two parties. However, these methods suffer diminished accuracy for large key lengths or in the presence of ambient noise. This work takes a different perspective to produce the desired channel measurements through adaptive manipulation of pilot signals for robust and accurate physical layer secret key generation. Specifically, an adaptive pilot manipulation scheme is designed not only to ensure that each channel episode has a unique pattern but also to improve pattern similarity between a pair of matched channel episodes, thus enabling high matching consistency. To validate the effectiveness of our method, we implement it by re-configuring software modules in GNU radio running on the USRP platform. Extensive experiments demonstrate that our method outperforms existing representative quantization-based and matching-based methods with improved key generation performance.
As an alternative and appealing approach to providing information security in wireless communication systems, secret key generation at physical layer has demonstrated its potential in terms of efficiency and reliability over traditional cryptographic methods. Without the necessity of a management centre for key distribution or reliance on computational complexity, physical layer key generation protocols enable two wireless entities to extract identical and dynamic keys from the randomness of the wireless channels associated with them.\nIn this thesis, the reliability of secret key generation at the physical layer is examined in practical wireless channels with imperfect channel state information (CSI). Theoretical analyses are provided to relate key match rate with channel's signal-to-noise ratio (SNR), degrees of channel reciprocity, and iterations of information reconciliation.\nIn order to increase key match rate of physical layer secret key generation, improved schemes in the steps of channel estimation and sample quantization are proposed respectively. In the channel estimation step, multiple observations of the wireless channels are integrated with a linear processor to provide a synthesized and more accurate estimation of the wireless channel. In the sample quantization step, a magnitude based quantization method with two thresholds is proposed to quantize partial samples, where specific quantization areas are selected to reduce cross-over errors. Significant improvements in key match rate are proven for both schemes in theoretical analysis and numerical simulations. Key match rate can even achieve 100% in both schemes with the assistance of information reconciliation process.\nIn the end, a practical application of physical layer secret key generation is presented, where dynamic keys extracted from the wireless channels are utilized for securing secret data transmission and providing efficient access control.
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.
Abstract Wireless communications between two devices can be protected by secret keys. However, existing key generation schemes suffer from the high bit disagreement rate and low bit generation rate. In this paper, we propose an efficient physical layer key generation scheme by exploring the Received Signal Strength (RSS) of signals. In order to reduce the high mismatch rate of the measurements and to increase the key generation rate, a pair of transmitter and receiver separately apply adaptive quantization algorithm for quantifying the measurements. Then, we implement a randomness extractor to further increase key generation rate and ensure randomness of generated of keys. Several real-world experiments are implemented to verify the effectiveness of the proposed scheme. The results show that compared with the other related schemes, our scheme performs better in bit generation rate, bit disagreement rate, and randomness.
Physical layer key generation is an important handshaking step for establishing secure wireless communication in wireless networks. Existing methods based on fine-grained Channel State Information (CSI) have seen significant limitations. Reciprocity, the theoretical basis of physical layer key generation, is sensitive to factors such as noise, interference and hardware level variations. Feedback-based Channel Gain Complement is designed to conquer the imperfect reciprocity between two communication parties in actual environments. In addition, we have found that the adjacent subcarriers are strongly correlated. Quantizing all 30 subcarriers without discrimination will reduce the randomness and strength of the secret key while discarding some carriers will lose important information. We propose a cluster-based quantization method, which balances between the generation speed and consistency in initial key bits. Evaluation results in static and mobile scenarios have shown that under the sampling rate of 5 packet/sec, Bit Generation Rate can reach 20~ 26 bps, and the generated key sequence can pass the NIST standard randomness test.
There is a growing interest in physical layer security. Recent work has demonstrated that wireless devices can generate a shared secret key by exploiting variations in their channel. The rate at which the secret bits are generated, however, depends heavily on how fast the channel changes. As a result, existing schemes have a low secrecy rate and are mainly applicable to mobile environments. In contrast, this paper presents a new physical-layer approach to secret key generation that is both fast and independent of channel variations. Our approach makes a receiver jam the signal in a manner that still allows it to decode the data, yet prevents other nodes from decoding. Results from a testbed implementation show that our method is significantly faster and more accurate than state of the art physical-layer secret key generation protocols. Specifically, while past work generates up to 44 secret bits/s with a 4% bit disagreement between the two devices, our design has a secrecy rate of 3-18 Kb/s with 0% bit disagreement.