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arXiv:1507.00095 · IEEE Transactions on Wireless Communications

Secret Key Agreement With Large Antenna Arrays Under the Pilot Contamination Attack

Sanghun Im, Hyoungsuk Jeon, Jinho Choi, Jeongseok Ha

Published Jul 15, 2015• 27 citations
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Abstract

We present a secret key agreement (SKA) protocol for a multi-user time-division duplex system where a base-station (BS) with a large antenna array (LAA) shares secret keys with users in the presence of non-colluding eavesdroppers. In the system, when the BS transmits random sequences to legitimate users for sharing common randomness, the eavesdroppers can attempt the pilot contamination attack (PCA) in which each of eavesdroppers transmits its target user's training sequence in hopes of acquiring possible information leak by steering beam towards the eavesdropper. We show that there exists a crucial complementary relation between the received signal strengths at the eavesdropper and its target user. This relation tells us that the eavesdropper inevitably leaves a trace that enables us to devise a way of measuring the amount of information leakage to the eavesdropper even if PCA parameters are unknown. To this end, we derive an estimator for the channel gain from the BS to the eavesdropper and propose a rate-adaptation scheme for adjusting the length of secret key under the PCA. Extensive analysis and evaluations are carried out under various setups, which show that the proposed scheme adequately takes advantage of the LAA to establish the secret keys under the PCA.

DOI
10.1109/twc.2015.2456894

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We present a secret key agreement (SKA) protocol for a multi-user time-division duplex system where a base-station (BS) with a large antenna array (LAA) shares secret keys with users in the presence of non-colluding eavesdroppers. In the system, when the BS transmits random sequences to legitimate users for sharing common randomness, the eavesdroppers can attempt the pilot contamination attack (PCA) in which each of eavesdroppers transmits its target user's training sequence in hopes of acquiring possible information leak by steering beam towards the eavesdropper. We show that there exists a crucial complementary relation between the received signal strengths at the eavesdropper and its target user. This relation tells us that the eavesdropper inevitably leaves a trace that enables us to devise a way of measuring the amount of information leakage to the eavesdropper even if PCA parameters are unknown. To this end, we derive an estimator for the channel gain from the BS to the eavesdropper and propose a rate-adaptation scheme for adjusting the length of secret key under the PCA. Extensive analysis and evaluations are carried out under various setups, which show that the proposed scheme adequately takes advantage of the LAA to establish the secret keys under the PCA.
We consider secret key agreement (SKA) over time division duplex for a multi-user wireless system, in which a base station (BS) equipped with a large antenna array remotely generates different secret keys for multiple users in the system. The BS can have the SKA over downlink broadcast channels with precoding based on uplink training from the multiple users. In this case, unfortunately, an eavesdropper can effectively perform a pilot contamination attack (PCA) by transmitting a targeted user's training sequence for the purpose to steer beam direction toward the eavesdropper. As the beam direction becomes under the eavesdroppers control, this PCA can result in information leakage from the BS to the targeted user. In order to fend off this PCA, we derive PCA detectors based on generalized likelihood ratio test and propose a countermeasure. For the performance analysis, we consider the outage probability and show that it decreases exponentially with the number of antennas at the BS, which cannot be achieved by the conventional SKA.
This work presents a secret key agreement (SKA) protocol for a multiuser time-division duplex cellular system under an active eavesdropping called pilot contamination attack (PCA) when the base station (BS) is equipped with a large antenna array. In particular, we study how to incorporate twoway training, i.e. conducting training processes in both the uplink and down-link transmissions, into the SKA protocol for the purpose of strengthening the protocol against the PCA and/or improving secret key generation efficiency. It will be shown that the two-way training provides the SKA protocol with a considerable enhencement of estimation for eavesdropper's channel. Secrecy performances of the proposed SKA protocol is quantitatively analyzed in terms of secrecy outage probability and average secret key rate, which shows that the two-way training improves the security performances especially in fast fading environments.
We consider a secret key agreement (SKA) protocol over time division duplex for a massive Multiple-Input-Multiple-Output (MIMO) system. As a security threat, we assume that a pilot contamination attack (PCA) is attempted by an eavesdropper for the purpose to gain information about the secret key. The eavesdropper controls its transmit power for the PCA in a way to maximize the amount of eavesdropping information, while hiding her presence from legitimate users. To fend off this PCA, we consider a SKA protocol working with a PCA detector. Specifically, our SKA protocol suspends the key generation process to prevent information leakage to the eavesdropper if the PCA detector declares the presence of the PCA more than a certain number of times. Taking into account the best choice of the PCA power for the eavesdropper, we analyze an achievable length of generated secret key through our SKA protocol. Simulation results show that our SKA protocol effectively suppresses the eavesdropper's PCA power by adjusting a threshold determining the suspension of the PCA, and a positive length of secret key is achievable through our SKA protocol.
In this paper, we study the design of secure communication for time-division duplex multi-cell multi-user massive multiple-input-multiple-output (MIMO) systems with active eavesdropping. We assume that the eavesdropper actively attacks the uplink pilot transmission and the uplink data transmission before eavesdropping the downlink data transmission of the users. We exploit both the received pilot's and the received data signals for uplink channel estimation. We show analytically that when both the number of transmit antennas and the length of the data vector tend to infinity, the signals of the desired user and the eavesdropper lie in different eigenspaces of the received signal matrix at the base station, provided their signal powers are different. This finding reveals that decreasing (instead of increasing) the desired user's signal power might be an effective approach to combat a strong active attack from an eavesdropper. Inspired by this observation, we propose a data-aided secure downlink transmission scheme and derive an asymptotic achievable secrecy sum-rate expression for the proposed design. For the special case of a single-cell single-user system with independent and identically distributed fading, the obtained expression reveals that the secrecy rate scales logarithmically with the number of transmit antennas. This is the same scaling law as for the achievable rate of a single-user massive MIMO system in the absence of eavesdroppers. The numerical results indicate that the proposed scheme achieves significant secrecy rate gains compared with alternative approaches based on matched filter precoding with artificial noise generation and null space transmission.
Transmitter-side channel state information of the legitimate destination plays a critical role in physical layer secure transmissions. However, channel training procedure is vulnerable to the pilot spoofing attack (PSA) or pilot jamming attack (PJA) by an active eavesdropper (Eve), which inevitably results in severe private information leakage. In this paper, we propose a random channel training (RCT)-based secure downlink transmission framework for a time division duplex multiple antennas base station. In the proposed RCT scheme, multiple orthogonal pilot sequences (PSs) are simultaneously allocated to the legitimate user (LU), and the LU randomly selects one PS from the assigned PS set to transmit. Under either the PSA or PJA, we provide the detailed steps for the BS to identify the PS transmitted by the LU, and to simultaneously estimate channels of the LU and Eve. The probability that the BS makes an incorrect decision on the PS of the LU is analytically investigated. Finally, closed-form secure beamforming vectors are designed and optimized to enhance the secrecy rates during the downlink transmissions. Numerical results show that the secrecy performance is greatly improved compared to the conventional channel training scheme wherein only one PS is assigned to the LU.
In this paper, the achievable secrecy rate of a relay-assisted massive multiple-input multiple-output (MIMO) downlink is investigated in the presence of a multi-antenna active/passive eavesdropper. The excess degrees-of-freedom offered by a massive MIMO base-station (BS) are exploited for sending artificial noise (AN) via random and null-space precoders. An active eavesdropper contaminates the uplink channel estimates by sending pilot sequences identical to those of the legitimate users/relay. This active pilot contamination makes the massive MIMO BS implicitly beamform the confidential signals toward the active eavesdropper during two-hop downlink transmissions. The achievable secrecy rates are derived by taking the detrimental effects of actively contaminated channel state information with estimation errors and spatially correlated fading at the multiple-antenna terminals into account. The secrecy rate loss incurred by active pilot attacks over passive eavesdropping is investigated, and the secrecy rate gap between random and null-space-based AN is compared. A novel transmit power control policy is designed to efficiently allocate transmit power at the BS/relay for payload data and AN sequences for maximizing the achievable secrecy rate. Our results reveal that active pilot contamination attacks significantly degrade the achievable secrecy rate in dual-hop transmissions, and the corresponding detrimental effects cannot be asymptotically mitigated in the infinite BS antenna regime.