Physical layer security is a method to ensure the confidentiality of a wireless communication from encryption keys exploiting the randomness of the reciprocal propagation channel between a pair of legitimate users, Alice and Bob. This confidentiality is achieved owing to the decorrelation between these channels and that experienced by a third terminal (Eve), acting as an eavesdropper. In this work, we evaluate the secret key capacity of a simple channel model, based on a disc of scatterers. The model allows to consider any distance between Bob and Eve within the disc, thus is not limited to a spatial stationarity, and is suitable to investigate the impact on the security of multiple antennas.
Physical layer security is a method to ensure the confidentiality of a wireless communication from encryption keys exploiting the randomness of the reciprocal propagation channel between a pair of legitimate users, Alice and Bob. This confidentiality is achieved owing to the decorrelation between these channels and that experienced by a third terminal (Eve), acting as an eavesdropper. In this work, we evaluate the secret key capacity of a simple channel model, based on a disc of scatterers. The model allows to consider any distance between Bob and Eve within the disc, thus is not limited to a spatial stationarity, and is suitable to investigate the impact on the security of multiple antennas.
Secret key generation (SKG) from the randomness provided by random channels is currently considered as one way to improve security in wireless communications at the physical layer level. However, the relation between the performance of SKG schemes and the characteristics of the radio channel has been moderately investigated. In this work, we evaluate the security performance on the basis of a simple channel model based on scatterers distributed around terminals, which enables going beyond the common assumption of spatial stationarity between the legitimate terminal and the eavesdropper. This performance is assessed both from information theory metrics and from a practical key extraction algorithm. Owing to the model flexibility, we evaluate the impact of several major channel characteristics such as the distribution and density of scatterers or the existence of a dominant LOS path.
Abstract Physical layer security is a method of extracting encryption keys according to the randomness of reciprocal propagation channels between legitimate users, and the security under normal circumstances is ensured according to the decorrelation between these channels and those tapped by eavesdropper. However, evidences show that in some scenarios, such as the environment of quasi-static or insufficient scattering, the tapped channel still has a strong correlation with the legitimate channel, leading to bits leakage and security imperilment of key generation. The effect of introducing scatterers has been experimentally proved, however, these studies are based on fixed positions or special models and there is yet a lack of research on the influences brought by various scatterer distributions. In this paper, we introduce scatterers into single-bounced DISC model and control their distributions through a probability density function with two degrees of freedom, aiming to deeply investigate the impacts of scatterer distribution on channel decorrelation as well as key security. Simulation results prove that spiral correlation between tapped channel and legitimate channel can be effectively reduced by increasing scatterers and arranging them around the legitimate receiver, which make contributions to reduce key leakage and improve security.
The wireless channel is inherently an open medium which exposes wireless communication users to the risk of interception. The vulnerabilities of the wireless channel have led to the search for innovative and efficient security solutions at different levels of the network protocol. In particular, the physical layer level allows for implementing some security functions, such as key generation and exchange, by exploiting the intrinsic randomness of the wireless communication channel. In this paper, we analyze the effect of wireless channel and of antenna characteristics on physical layer security (PLS) key generation. The aim is to put in evidence the relation between physical quantities, such as radio channel characteristics or antenna directivity, with higher level secrecy performance indicators, such as the key mismatch between the different communication nodes and the key randomness. For this purpose, we developed a comprehensive numerical model, which implements all the different steps, from signal generation and wireless propagation modeling to key generation through spectral quantization. The reported results show that the multipath richness of the radio channel, as in outdoor urban scenarios, improves the PLS secrecy performances with respect to simpler propagation scenarios. Moreover, we show that the use of more directive antennas in the legitimate communication link improves secrecy. An opposite effect is achieved when the directivity of the eavesdropper antenna is increased, thus improving its ability to perform passive attacks.
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 %.
Physical layer security (PLS) is a new paradigm aiming at securing communications between legitimate parties at the physical layer. Conventionally, achieving confidentiality in communication networks relies on cryptographic techniques such as public-key cryptography, secret-key distribution and symmetric encryption. Such techniques are deemed secure based on the assumption of limited computational abilities of a wiretapper. Given the relentless progress in computational capacities and the dynamic topology and proliferation of modern wireless networks, the relevance of the previous techniques in securing communications is more and more questionable and less and less reliable. In contrast to this paradigm, PLS does not assume a specific computational power at any eavesdropper, its premise to guarantee provable security via employing channel coding techniques at the physical layer exploiting the inherent randomness in most communication systems. In this dissertation, we investigate a particular aspect of PLS, which is secret-key agreement, also known as secret-sharing. In this setup, two legitimate parties try to distill a secret-key via the observation of correlated signals through a noisy wireless channel, in the presence of an eavesdropper who must be kept ignorant of the secret-key. Additionally, a noiseless public channel is made available to the legitimate parties to exchange public messages that are also accessible to the eavesdropper. Recall that key agreement is an important aspect toward realizing secure communications in the sense that the key can be used in a one-time pad scheme to send the confidential message. In the first part, our focus is on secret-sharing over Rayleigh fading quasi-static channels. We study the fundamental relationship relating the probability of error and a given target secret-key rate in the high power regime. This is characterized through the diversity multiplexing tradeoff (DMT) concept, that we define for our model and then characterize it. We show that the impact of the secrecy constraint is to reduce the effective number of transmit antennas by the number of antennas at the eavesdropper. Toward this characterization, we provide several schemes achieving the DMT and we highlight disparities between coding for the wiretap channel and coding for secret-key agreement. In the second part of the present work, we consider a fast-fading setting in which the wireless channels change during each channel use. We consider a correlated environment where transmit, legitimate receiver and eavesdropper antennas are correlated. We characterize the optimal strategy achieving the highest secret-key rate. We also identify the impact of correlation matrices and illustrate our analysis with various numerical results. Finally, we study the system from an energy-efficiency point of view and evaluate relevant metrics as the minimum energy required for sharing a secret-key bit and the wideband slope.
There is growing interest in physical-layer security methods that exploit the random nature of the physical propagation channel to strengthen existing crypto-systems. In reciprocal channel key generation (RCKG), legitimate nodes (Alice and Bob) observe a common fluctuating channel to generate keys that are safe from the eavesdropper (Eve). Previous work [1, 2] derived expressions for the available key bits and those safe from an eavesdropper for MIMO systems with correlated complex Gaussian statistics. This paper applies these expressions to new MIMO measurements in indoor LOS and NLOS environments, indicating how propagation effects limit secure key generation and what key generation rates can be expected in practice.