Fingerprints in the Ether: Using the Physical Layer for Wireless Authentication

Abstract

Abstract-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 fact that, in a typically rich scattering environment, the radio channel response decorrelates quite rapidly in space. Specifically, we describe a physical-layer algorithm that combines channel probing (M complex frequency response samples over a bandwidth W ) with hypothesis testing to determine whether current and prior communication attempts are made by the same user (same channel response). In this way, legitimate users can be reliably authenticated and false users can be reliably detected. To evaluate the feasibility of our algorithm, we simulate spatially variable channel responses in real environments using the WiSE ray-tracing tool; and we analyze the ability of a receiver to discriminate between transmitters (users) based on their channel frequency responses in a given office environment. For several rooms in the extremities of the building we considered, we have confirmed the efficacy of our approach under static channel conditions. For example, measuring five frequency response samples over a bandwidth of 100 MHz and using a transmit power of 100 mW, valid users can be verified with 99% confidence while rejecting false users with greater than 95% confidence.

Channel-based spoofing detection in frequency-selective rayleigh channels

“…This error is zero-mean and independent across frequencies and receive antennas, with a common variance 2 . Another impairment, often omitted in channel estimation models [10]- [13], is interference from other radio users. We can model the interference effect on channel estimation as contributing a random error component, ( ), to the true value of each measured channel gain.…”

“…Since decreases monotonically with , Bob can conveniently find the test threshold that reaches the required . The performance of the scheme depends on several system parameters in addition to the correlation coefficient , as given by the 0 (⋅) term in (10). One is the signal-to-(interferenceplus-noise) ratio (SINR) of the channel estimates for Alice, defined by…”

“…Several physical-layer authentication techniques have been proposed to enhance security in wireless networks, exploiting the physical-layer information such as the received signal strength (RSS) [4], [7], [8], channel impulse response (CIR) [9], and channel frequency response (CFR) [10]- [13].…”

“…As a benchmark, we first investigated the channel-based spoofing detection for time-invariant path gains, [10]. Then the impact of channel time variations and terminal mobility were studied in [11] and [13], respectively.…”

“…Our previous work [10]- [13] has partly addressed these impairments and validated the efficacy of the channel-based authentication for various cases, notably, environmental changes [11], and terminal mobility [13]. However, these studies are limited by virtue of using different heuristic test statistics for each scenario.…”