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arXiv:1101.3774 · International Journal of Advanced Computer Science and Applications

Secret Key Agreement Over Multipath Channels Exploiting a Variable-Directional Antenna

Коржик Валерий Иванович, Viktor Yakovlev, Yuri Kovajkin, Guillermo B. Morales-Luna

Published Jan 1, 2012• 11 citations
arXivHTMLPDF

Abstract

We develop an approach of key distribution protocol(KDP) proposed recently by T.Aono et al., where the security of KDP is only partly estimated in terms of eavesdropper's key bit errors. Instead we calculate the Shannon's information leaking to a wire tapper and also we apply the privacy amplification procedure from the side of the legal users. A more general mathematical model based on the use of Variable-Directional Antenna (VDA) under the condition of multipath wave propagation is proposed. The new method can effectively be used even in noiseless interception channels providing thus a widened area with respect to practical applications. Statistical characteristics of the VDA are investigated by simulation, allowing to specify the model parameters. We prove that the proposed KDP provides both security and reliability of the shared keys even for very short distances between legal users and eavesdroppers. Antenna diversity is proposed as a mean to enhance the KDP security. In order to provide a better performance evaluation of the KDP, it is investigated the use of error correcting codes.

DOI
10.14569/ijacsa.2012.030127

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We develop an approach of key distribution protocol(KDP) proposed recently by T.Aono et al., where the security of KDP is only partly estimated in terms of eavesdropper's key bit errors. Instead we calculate the Shannon's information leaking to a wire tapper and also we apply the privacy amplification procedure from the side of the legal users. A more general mathematical model based on the use of Variable-Directional Antenna (VDA) under the condition of multipath wave propagation is proposed. The new method can effectively be used even in noiseless interception channels providing thus a widened area with respect to practical applications. Statistical characteristics of the VDA are investigated by simulation, allowing to specify the model parameters. We prove that the proposed KDP provides both security and reliability of the shared keys even for very short distances between legal users and eavesdroppers. Antenna diversity is proposed as a mean to enhance the KDP security. In order to provide a better performance evaluation of the KDP, it is investigated the use of error correcting codes.
It has been proposed recently an approach to generate secret key exploiting reactance-domain scalar response of multipath fading channel. However, the security of the shared key has not been adequately investigated. In this paper we propose a mathematical model of the key distribution protocol based on the use of a Variable-Directional Antenna (VDA) acting on multipath wireless channels. The security of the key distribution protocol (KDP) is estimated in terms of Shannon's information leaking to an eavesdropper. Statistical properties of VDA are investigated by simulation that results in an opportunity to calculate the security of the KDP depending on the mutual locations of the legal user and the eavesdropper. Antenna diversity is considered as a measure to enhance a level of the KDP security.
As a way to ensure security on wireless communication, a secret key agreement scheme exploiting the unique properties of the wireless medium, the reciprocity of radio propagation and the irregularity of multipath fading, is being proposed [1-3]. The method enables two legitimate users to share a secret key without distributing the actual key, by using the radio propagation channel between the two as a common and exclusive source of randomness upon which a secret key could be derived. As an application of this scheme to environments where the radio propagation characteristics are static, a method employing a variable directivity antenna called the ESPAR antenna [4] has been known to be effective. In this method, secret keys are generated from received signal strength indicator (RSSI) sequences of legitimate users. One known problem of this method is that in environments with simple radio propagation characteristics such as a rectangular room of concrete with no fixtures, the strength of the direct wave becomes the dominant factor affecting the fluctuation of the RSSI, thus increasing the chance for eavesdroppers located near the path of such waves to estimate the secret key. Since all previous considerations of the aforementioned scheme has been done with environments where the legitimate users are in line-of-sight, this paper aims to illustrate how the location of eavesdroppers affect the secrecy of keys generated with the scheme, in a radio propagation environment with no clearly dominant wave. The key capacity in respect to the position of the eavesdropper in such environment is shown using computer simulations.
The method of key sharing between a mobile unit and a base station through a wireless MIMO-based fading channel is investigated.The description of a key distribution protocol is given.The expression to estimate the correct key bit agreement based on the use of guard interval is proved.Statistical properties of the key string are tested using the NIST criteria.Impossibility of key string eavesdropping by illegal users is guaranteed due to small values of correlation between legal and eavesdropper carrier phases.Numerical examples show that the MIMO system with 8 antennas is able to agree 256 bits with a reliability value 0.99 for SNR equal to 35 dB.This experiment confirms that the MIMO scenario is especially effective for secret key distribution.
A less expensive and more flexible solution to the problem of sharing secret keys between wireless nodes is to use the inherent randomness in the wireless channel between them as the source for extracting bits of the secret key between these nodes. We propose a new secret key distribution approach that utilizes the uniformly distributed phase information of channel responses to extract shared cryptographic keys under narrowband multipath fading models. Compared to existing approaches which only support pair wise key distribution, our scheme is highly scalable and can support efficient group key distribution. Various key distribution schemes are appraised to determine the level of security and connectivity. Simulated results show that key distribution exploiting channel phase has improved resilience against node capture. them as the source for extracting bits of the secret key between these nodes. Shared secret key distribution from channel measurements is an application which benefits from the randomnessof the multipath channel. It would not, for example, work in a truly free-space environment (such as deep space radio links). Secret sharing benefits from: • Reciprocity of the wireless radio channel: The multipath properties of the radio channel (gains, phase shifts, and delays) at any point in time and on any given frequency channel are identical on both directions of the link. • Temporal variations in the radio channel: Over time, the multipath channel changes due to movement of either end of the link, and any motion of people and objects in the environment near the link. An application may specifically request a user to move or shake the wireless device in order to generate more temporal variation. • Spatial variations: The properties of the radio channel are unique to the locations of the two endpoints of the link. An eavesdropper at a third location more than a few wavelengths from either endpoint will measure a different, uncorrelated radio channel. The proposed scheme is more flexible and can be applied in both static and mobile environments. Our scheme introduces phase randomness to bit distribution and removes the reliance on node mobility to obtain high entropy bits. We evaluate the proposed schemes through both analytical and simulation studies. The parameters of the scheme can be selected such that a desired level of key distribution accuracy and reliability is achieved with high efficiency.
We consider a source model for information theoretic secret key agreement based on the distance among the nodes, in a basic system consisting of two legitimate users and an eavesdropper. The legitimate nodes try to agree on a reliable and secure key based on their noisy observation of distance between them. We propose two methods to enhance system utility: 1) Artificial Noise Forwarding (ANF), 2) transmission in different beam directions (multi-antenna transmission). In the first method artificial noise is used to worsen e a vesdropper's distance estimation and in the second method beacon signals are sent in different directions and the virtual distances in different beam directions are used as the randomness sources. We show that if eavesdropper is not equipped with multi-directional antenna, then ANF is a useful method while in the case of users equipped with multi-directional antenna, transmitting in different directions is a suitable way to increase the secret key rate.
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.