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IEEE International Conference on Communications workshops

Secure Communications in Line-of-Sight Scenarios by Rotation-based Secret Key Generation

Thuy M. Pham, Andre Noll Barreto, Miroslav Mitev, Maximilian Matthé, Gerhard Paul Fettweis

Published May 16, 2022• 8 citations
Publisher

Abstract

In this paper, we evaluate the achievable rates of the physical layer security (PLS)-based secret key generation (SKG) in a line-of-sight (LoS) channel, which occurs with a high probability in unmanned aerial vehicle (UAV) communications. SKG is a promising technique for lightweight scalable key distribution, and, despite the mature theory of PLS, this technique remains to be seen in practical applications. Thus, modelling realistic scenarios is of particular interest. One of the reasons why SKG has not been used in practice is due to the deterministic properties of LoS channels. To overcome this problem, in this paper we propose the rotation of the device antennas as an entropy source, reflected by the channel phases, from which the keys are derived. Simulation results show that by utilizing rotation in LoS scenarios, a number of secret bits can be generated, also given the presence of an eavesdropper. It is also shown that by controlling the transmit power we can maximize the conditional mutual information.

DOI
10.1109/iccworkshops53468.2022.9814519

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In this paper, we evaluate the achievable rates of the physical layer security (PLS)-based secret key generation (SKG) in a line-of-sight (LoS) channel, which occurs with a high probability in unmanned aerial vehicle (UAV) communications. SKG is a promising technique for lightweight scalable key distribution, and, despite the mature theory of PLS, this technique remains to be seen in practical applications. Thus, modelling realistic scenarios is of particular interest. One of the reasons why SKG has not been used in practice is due to the deterministic properties of LoS channels. To overcome this problem, in this paper we propose the rotation of the device antennas as an entropy source, reflected by the channel phases, from which the keys are derived. Simulation results show that by utilizing rotation in LoS scenarios, a number of secret bits can be generated, also given the presence of an eavesdropper. It is also shown that by controlling the transmit power we can maximize the conditional mutual information.
In this paper, the feasibility of implementing a lightweight key distribution scheme using physical layer security for secret key generation (SKG) is explored. Specifically, we focus on examining SKG with the received signal strength (RSS) serving as the primary source of shared randomness. Our investigation centers on a frequency-selective line-of-sight (LoS) multipath channel, with a particular emphasis on assessing SKG rates derived from the distributions of RSS. We derive the received signal distributions based on how the multipath components resolve at the receiver. The mutual information (MI) is evaluated based on LoS 3GPP channel models using a numerical estimator. We study how the bandwidth, delay spread, and Rician K-factor impact the estimated MI. This MI then serves as a benchmark setting bounds for the SKG rates in our exploration.
The mutual information of the observed channel phase between devices can serve as an entropy source for secret key generation in line-of-sight scenarios. However, so far only simulated and numeric results were available. This paper derives the probability distribution of the channel phase and corresponding expressions for the mutual information. Moreover, the orientation distribution is optimized in order to maximize the mutual information. All presented results are validated numerically. These outcomes serve as a basis for further analytic investigations on the secret key generation rate and subsequent physical layer security performance analysis in line-of-sight scenarios, such as those encountered in drone-aided communications.
Unmanned aerial vehicle (UAV) will be an essential carrier for future wireless communications due to its flexible deployment and low cost. As such, the information security of UAV communications is of paramount concern. In this paper, a novel physical layer secret key generation scheme is proposed for air-to-ground (A2G) UAV multiple-input-multiple-output (MIMO) communications, which is applicable in frequency division duplex (FDD) systems. In UAV communications, line-of-sight (LoS) propagation is a distinctive feature, which significantly weakens the performance of channel state information (CSI) based keys. Therefore, a novel channel parameter, three-dimension (3D) spatial angle, is employed to combat against a novel active eavesdropping method, which is termed as Environment Reconstruction based Attack for SEcret keys (ERASE). Compared to the existing plane-angle-based method, our scheme can efficiently utilize spatial resources and provide a higher key generation rate (KGR). The advantages of the proposed scheme are shown through both theoretical analysis and simulations.
Physical layer security (PLS) can be adopted for efficient key sharing in secured wireless systems. The random nature of the wireless channel and channel reciprocity (CR) are the main pillars for realizing PLS techniques. However, for applications that involve air-to-air (A2A) transmission, such as unmanned aerial vehicle (UAV) applications, the channel does not generally have sufficient randomness to enable reliable key generation. Therefore, this work proposes a novel system design to mitigate the channel randomness constraint and enable high-rate secret key generation (SKG) process. The proposed system integrates physically unclonable functions (PUFs) and CR principle to securely exchange secret keys between two nodes. Moreover, an adaptive and controllable artificial fading (AF) level with interleaving is used to mitigate the impact of low randomness variations in the wireless channel. The proposed system can operate efficiently even when the channel is nearly flat or time invariant. Consequently, the time required for generating and sharing a key is significantly shorter than conventional techniques. We also propose a novel bit extraction scheme that reduces the number of overhead bits required to share the intermediate keys. The obtained Monte Carlo simulation results show that a key agreement can be reached at the first trial for moderate and high signal-to-noise ratios (SNRs), which is substantially faster than other PLS techniques. Moreover, the results show that inducing AF into static channels reduces the mismatch ratio between the generated secret sequences and degrades the eavesdropper’s capability to predict the secret keys.
In this paper, we address physical-layer key generation between two unmanned aerial vehicles (UAVs) in flight, which are hindered by a dominant line-of-sight component (LOS) in their wireless channel. Although strong LOS component yields better error-performance in data transmission, it is well known that limited randomness in the channel variation will render the underlying physical-layer key generation algorithms ineffective. Pointing at this disadvantage, we explore a relay-based secret-key generation technique between the two UAVs, wherein a ground- stationed relay assists the two UAVs to witness a common source of randomness with higher entropy than their direct channel. We propose the Relay- Assisted Selective Inversion (RASI) protocol, which selectively offers common randomness from either of the channels from the relay to the two UAVs. To showcase the benefits of the RASI protocol, we first obtain theoretical lower bounds on the differential entropy of the common source of randomness, and subsequently employ a practical key-generation algorithm to synthesize the digital keys. We show that RASI can help the two UAVs to generate keys with higher key-rate than using the direct channel only. Finally, we also show that RASI outperforms an existing state-of-the-art relay-based method in terms of key-rate and computational complexity at the UAVs, while marginally losing to the latter in communication- overhead.
Physical Layer Security (PLS) is emerging as an innovative solution to enhance the security of wireless communications. This work analyzes the impact of a realistic indoor radio propagation on Secrecy Key Generation (SKG) in a Wi-Fi application scenario. This PLS technique is based on the extraction of raw cryptographic keys, taking advantage of the radio propagation phenomena as a source of entropy. In detail, we considered two legitimate nodes, i.e., Alice and Bob, which use the SKG to extract keys from the channel, and a malicious node, i.e., Eve, which acts as a passive eavesdropper and tries to discover the key. The reported results show that legitimate nodes key mismatch is strongly influenced by noise contribution, and the eavesdropper attack performs better with a higher Line-of-Sight (LoS) contribution. Conversely, when the power is evenly spread over all the multipath components, the eavesdropped key mismatch is maintained in the range of 30 – 50 %.