The wireless medium contains domain-specific information that can be used to complement and enhance traditional security mechanisms. In this paper we propose ways to exploit the spatial variability of the radio channel response in a rich scattering environment, as is typical of indoor environments. Specifically, we describe a physical-layer authentication algorithm that utilizes channel probing and hypothesis testing to determine whether current and prior communication attempts are made by the same transmit terminal. In this way, legitimate users can be reliably authenticated and false users can be reliably detected. We analyze the ability of a receiver to discriminate between transmitters (users) according to their channel frequency responses. This work is based on a generalized channel response with both spatial and temporal variability, and considers correlations among the time, frequency and spatial domains. Simulation results, using the ray-tracing tool WiSE to generate the time-averaged response, verify the efficacy of the approach under realistic channel conditions, as well as its capability to work under unknown channel variations.
More recently, the wireless channel has been explored as a new form of fingerprint for wireless security. The reciprocity and rich multipath of the ultrawideband channel has been used as a means to establish encryption keys @cite_15 . In @cite_14 , a practical scheme to discriminate between transmitters was proposed and identifies mobile devices by tracking measurements of signal strength from multiple access points. A similar approach was considered for sensor networks in @cite_4 . Concurrent to these efforts, the present authors have built a significance test that exploits the spatial variability of propagation to enhance the authentication in the stationary, time-invariant channel @cite_3 . In this paper, we have significantly expanded the method to cover a more generalized channel, where there are time variations due to changes in the environment. As in @cite_3 , however, the ends of the link remain stationary, as might be the case for a population of users sitting in a room or airport terminal. We will see that, in some cases, the time variations the authentication.
@cite_15 @cite_14 @cite_4 @cite_3
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The wireless medium contains domain-specific information that can be used to complement and enhance traditional security mechanisms. In this paper we propose ways to exploit the spatial variability of the radio channel response in a rich scattering environment, as is typical of indoor environments. Specifically, we describe a physical-layer authentication algorithm that utilizes channel probing and hypothesis testing to determine whether current and prior communication attempts are made by the same transmit terminal. In this way, legitimate users can be reliably authenticated and false users can be reliably detected. We analyze the ability of a receiver to discriminate between transmitters (users) according to their channel frequency responses. This work is based on a generalized channel response with both spatial and temporal variability, and considers correlations among the time, frequency and spatial domains. Simulation results, using the ray-tracing tool WiSE to generate the time-averaged response, verify the efficacy of the approach under realistic channel conditions, as well as its capability to work under unknown channel variations. The multipath-rich wireless environment associated with typical wireless usage scenarios is characterized by a fading channel response that is time-varying, location-sensitive, and uniquely shared by a given transmitter-receiver pair. The complexity associated with a richly scattering environment implies that the short-term fading process is inherently hard to predict and best modeled stochastically, with rapid decorrelation properties in space, time, and frequency. In this paper, we demonstrate how the channel state between a wireless transmitter and receiver can be used as the basis for building practical secret key generation protocols between two entities. We begin by presenting a scheme based on level crossings of the fading process, which is well-suited for the Rayleigh and Rician fading models associated with a richly scattering environment. Our level crossing algorithm is simple, and incorporates a self-authenticating mechanism to prevent adversarial manipulation of message exchanges during the protocol. Since the level crossing algorithm is best suited for fading processes that exhibit symmetry in their underlying distribution, we present a second and more powerful approach that is suited for more general channel state distributions. This second approach is motivated by observations from quantizing jointly Gaussian processes, but exploits empirical measurements to set quantization boundaries and a heuristic log likelihood ratio estimate to achieve an improved secret key generation rate. We validate both proposed protocols through experimentations using a customized 802.11a platform, and show for the typical WiFi channel that reliable secret key establishment can be accomplished at rates on the order of 10 b s. We propose an enhanced physical-layer authentication scheme for multi-carrier wireless systems, where transmission bursts consist of multiple frames. More specifically, it is based on the spatial variability characteristic of wireless channels, and able to work with moderate terminal mobility. For the authentication of the first frame in each data burst, the legal transmitter uses the saved channel response from the previous burst as the key for authentication of the first frame in the next burst. The key is obtained either via feedback from the receiver, or using the symmetric channel property of a TDD system. Then the authentication of the following frames in the burst is performed either by a Neyman-Pearson hypothesis test, or a least-squares adaptive channel estimator. Simulations in a typical indoor building show that the scheme based on the Neyman-Pearson test is more robust against terminal mobility, and is able to detect spoofing attacks efficiently with small system overhead when the terminal moves with a typical pedestrian speed. The broadcast nature of the wireless medium poses a serious challenge to the security of wireless communications and networks. Traditional computational security strategies always fail to prevent the eavesdropper from overhearing the communications. Recently, the unique characteristics of wireless channel fingerprints, e.g. randomness and reciprocity, have been successfully used to enhance the security of the wireless network. We expand our previous work on exploring particular physical parameters of fingerprints, and focus on a new scheme in which we use the RAKE receiver to differentiate users under low transmission power. RAKE receiver may capture and estimate fingerprints through poor autocorrelation of the spreading coding. As the fingerprint is incomputable and unpredictable, and may only be detected by the pair of transmitter and receiver, it may be fully utilized to design an efficient authentication method. Simulation results strongly verify the efficiency of our proposed method, especially in the case of low SNR.