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.
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.
Unmanned aerial vehicles (UAVs) have attracted much attention for civil and military uses because of their high mobility and adaptable deployment capabilities in open spaces. They facilitate agile communications and ubiquitous connectivity. UAVs benefit from dominant line-of-sight communication links but are more susceptible to adversary eavesdropping attacks. Since upper-layer cryptography methods may be insufficient, physical-layer security (PLS) is an attractive alternative. PLS capitalizes on the inherent randomness of wireless channels to improve information confidentiality, particularly in UAV systems. This article provides a comprehensive overview of PLS in the context of UAV systems, examining various communication channels, including ground-to-air (G2A), ground-to-ground (G2G), air-to-ground (A2G), and air-to-air (A2A). First, we give a general review of UAV communications, emphasizing its functions as user equipment, base station (BS), and mobile relay. Following that, we provide an overview of PLS and its forms. The survey organizes the most advanced PLS techniques against passive wireless eavesdropping regarding the channels they are designed to protect. These schemes are further categorized into optimization and secrecy performance analysis. We examine technical aspects within each sub-category and classify core contributions based on approaches and objectives to improve secrecy performance. Moreover, we added summary tables of the identified schemes considering optimization and secrecy performance analysis domains for each category, providing an in-depth understanding of their technical aspects. In addition, we discuss open research issues and identify future research directions to address evolving threats and requirements in UAV communications to improve information confidentiality.
In order to enhance the secrecy transmission of unmanned aerial vehicle (UAV) swarm, a novel physical-layer key generation (PLKG) efficient UAV swarm trajectory planning method is proposed in this work. Different from the existing UAV trajectory planning methods that only focus on collision avoidance, energy saving and improving transmission quality, the proposed method incorporates the PLKG capability into the UAV trajectory design. Based on the findings of the fact that the wireless scattering experienced by UAV signals from different UAV trajectories are typically distinct, the channel randomness oriented PLKG behaves differently for various UAV trajectories. As a result, we propose to incorporate the PLKG metric into the UAV trajectory planning objectives, in order to improve the secrecy of UAV swarm transmissions. The theoretical derivation between UAV swarm PLKG metric and the wireless scattering entropy is obtained, and we propose a channel entropy knowledge sharing mechanism for UAV swarm to achieve PLKG efficient swarm trajectory planning. Simulation results show that the key generation performance can be largely improved in comparison to the traditional secrecy rate maximization oriented UAV swarm trajectory planning.
With the rapid advancement of unmanned aerial vehicle (UAV), ensuring the security of communication links among UAVs has become crucial. In this paper, we propose a novel physical layer key generation scheme based on channel codeword reconstruction. In UAV communications, the high mobility of aerial nodes leads to short channel coherence time, which together with noise causes inevitable channel estimation errors. These errors significantly degrades the performance of wireless channel-based key generation. Therefore, we propose a codeword construction algorithm that achieves a polarization characteristic, which effectively segregates reliable keys from unreliable ones. Compared to the existing quantization-based key generation scheme, our approach maximize the utilization of raw channel information and employ soft-decision decoding to generate key. Simulation results demonstrate that the proposed scheme reduces the key disagreement rate for legitimate users and increases the number of consistently generated keys. Furthermore, our method ensures a lower key consistency rate for eavesdropper, which guarantees system security.
Due to its high mobility and flexible deployment, unmanned aerial vehicle (UAV) is drawing unprecedented interest in both military and civil applications to enable agile wireless communications and provide ubiquitous connectivity. Mainly operating in an open environment, UAV communications can benefit from dominant line-of-sight links; however, it on the other hand renders the UAVs more vulnerable to malicious eavesdropping or jamming attacks. Recently, physical layer security (PLS), which exploits the inherent randomness of the wireless channels for secure communications, has been introduced to UAV systems as an important complement to the conventional cryptography-based approaches. In this paper, a comprehensive survey on the current achievements of the UAV-aided wireless communications is conducted from the PLS perspective. We first introduce the basic concepts of UAV communications including the typical static/mobile deployment scenarios, the unique characteristics of air-to-ground channels, as well as various roles that a UAV may act when PLS is concerned. Then, we introduce the widely used secrecy performance metrics and start by reviewing the secrecy performance analysis and enhancing techniques for statically deployed UAV systems, and extend the discussion to a more general scenario where the UAVs' mobility is further exploited. For both cases, respectively, we summarize the commonly adopted methodologies in the corresponding analysis and design, then describe important works in the literature in detail. Finally, potential research directions and challenges are discussed to provide an outlook for future works in the area of UAV-PLS in 5G and beyond networks.
In unmanned aerial vehicle (UAV) swarm networks, a group secret key (GSK) is required to enable secured UAV-UAV communications, multicast, and broadcast transmission. Moreover, it can be used for device authentication. Therefore, this paper proposes an efficient GSK protocol denoted as the sequential secret group key (SSGK) algorithm for distributed UAV swarmsecured communications. The proposed protocol utilizes network coding to generate cooperation information that is transmitted on the channel and is uncorrelated with the generated secret key. The proposed protocol depends on the pairwise key generation (PKG) process between pairs of UAVs. However, not all possible pairwise agreements are performed to minimize the time and signaling overhead, i.e., the pairwise key agreement is performed only between selected UAVs as a compromise between the required overhead transmission resources and the achieved redundancy level. The obtained results show that a redundancy level of 4 is sufficient to provide a reliable GSK generation process. The results also show that the performance of the key generation process highly depends on the channelbit error rate (BER), the number of UAVs, and the key length.
Due to their flexible deployment and on-demand mobility, small-scale unmanned aerial vehicles (UAVs) are anticipated to be involved in widespread communication applications in the forthcoming fifth-generation networks. However, the confidentiality of UAV communication applications is vulnerable to security threats due to the broadcast nature and dominant line-of-sight channel conditions, and physical-layer security can be applied for secrecy performance enhancement in such a context. On the other hand, it is also promising to exploit UAVs to cooperatively protect secure communications. This article provides an overview of the recent research efforts on UAV-involved secure communications at the physical layer. We focus on the design of secure transmission schemes according to different roles of UAVs and the optimization of introduced degrees of freedom by the unique characteristics of UAVs. We also propose some future research directions on this topic.