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arXiv:2007.03201 · ACM Conference on Security and Privacy in Wireless and Mobile Networks (WiSec)

iJam with channel randomization

Jordan L. Melcher, Yao Rui Zheng, Dylan Anthony, Matthew Troglia, Thomas Yang, Alvin Yang, Samson Aggelopoulos, Yanjun Pan, Ming Li

Published Jul 8, 2020• 3 citations
arXivHTMLPDF

Abstract

Physical-layer key generation methods utilize the variations of the communication channel to achieve a secure key agreement between two parties with no prior security association. Their secrecy rate (bit generation rate) depends heavily on the randomness of the channel, which may reduce significantly in a stable environment. Existing methods seek to improve the secrecy rate by injecting artificial noise into the channel. Unfortunately, noise injection cannot alter the underlying channel state, which depends on the multipath environment between the transmitter and receiver. Consequently, these methods are known to leak key bits toward multi-antenna eavesdroppers, which is capable of filtering the noise through the differential of multiple signal receptions. This work demonstrates an improved approach to reinforce physical-layer key generation schemes, e.g., channel randomization. The channel randomization approach leverages a reconfigurable antenna to rapidly change the channel state during transmission, and an angle-of-departure (AoD) based channel estimation algorithm to cancel the changing effects for the intended receiver. The combined result is a communication channel stable in the eyes of the intended receiver but randomly changing from the viewpoint of the eavesdropper. We augmented an existing physical-layer key generation protocol, iJam, with the proposed approach and developed a full-fledged remote instrumentation platform to demonstrate its performance. Our evaluations show that augmentation does not affect the bit error rate (BER) of the intended receiver during key establishment but reduces the eavesdropper's BER to the level of random guessing, regardless of the number of antennas it equips.

DOI
10.1145/3395351.3401705

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Physical-layer key generation methods utilize the variations of the communication channel to achieve a secure key agreement between two parties with no prior security association. Their secrecy rate (bit generation rate) depends heavily on the randomness of the channel, which may reduce significantly in a stable environment. Existing methods seek to improve the secrecy rate by injecting artificial noise into the channel. Unfortunately, noise injection cannot alter the underlying channel state, which depends on the multipath environment between the transmitter and receiver. Consequently, these methods are known to leak key bits toward multi-antenna eavesdroppers, which is capable of filtering the noise through the differential of multiple signal receptions. This work demonstrates an improved approach to reinforce physical-layer key generation schemes, e.g., channel randomization. The channel randomization approach leverages a reconfigurable antenna to rapidly change the channel state during transmission, and an angle-of-departure (AoD) based channel estimation algorithm to cancel the changing effects for the intended receiver. The combined result is a communication channel stable in the eyes of the intended receiver but randomly changing from the viewpoint of the eavesdropper. We augmented an existing physical-layer key generation protocol, iJam, with the proposed approach and developed a full-fledged remote instrumentation platform to demonstrate its performance. Our evaluations show that augmentation does not affect the bit error rate (BER) of the intended receiver during key establishment but reduces the eavesdropper's BER to the level of random guessing, regardless of the number of antennas it equips.
Orthogonal blinding based schemes for wireless physical layer security aim to achieve secure communication by injecting noise into channels orthogonal to the main channel and corrupting the eavesdropper’s signal reception. These methods, albeit practical, have been proven vulnerable against multiantenna eavesdroppers who can filter the message from the noise. The vulnerability is rooted in the fact that the main channel state remains static in spite of the noise injection, which allows an eavesdropper to estimate it promptly via known symbols and filter out the noise. Our proposed scheme leverages a reconfigurable antenna for Alice to rapidly change the channel state during transmission and a compressive sensing based algorithm for her to predict and cancel the changing effects for Bob. As a result, the communication between Alice and Bob remains clear, whereas randomized channel state prevents Eve from launching the knownplaintext attack. We formally analyze the security of the scheme against both single and multi-antenna eavesdroppers and identify its unique anti-eavesdropping properties due to the artificially created fast-changing channel. We conduct extensive simulations and real-world experiments to evaluate its performance. Empirical results show that our scheme can suppress Eve’s attack success rate to the level of random guessing, even if she knows all the symbols transmitted through other antenna modes.
Physical-layer based key generation schemes exploit the channel reciprocity for secret key extraction, which can achieve information-theoretic secrecy against eavesdroppers. Such methods, although practical, have been shown to be vulnerable against man-in-the-middle (MitM) attacks, where an active adversary, Mallory, can influence and infer part of the secret key generated between Alice and Bob by injecting her own packet upon observing highly correlated channel/RSS measurements from Alice and Bob. As all the channels remain stable within the channel coherence time, Mallory's injected packets cause Alice and Bob to measure similar RSS, which allows Mallory to successfully predict the derived key bits. To defend against such a MitM attack, we propose to utilize a reconfigurable antenna at one of the legitimate transceivers to proactively randomize the channel state across different channel probing rounds. The randomization of the antenna mode at every probing round breaks the temporal correlation of the channels from the adversary to the legitimate devices, while preserving the reciprocity of the channel between the latter. This prevents key injection from the adversary without affecting Alice and Bob's ability to measure common randomness. We theoretically analyze the security of the protocol and conduct extensive simulations and real-world experiments to evaluate its performance. Our results show that our approach eliminates the advantage of an active MitM attack by driving down the probability of successfully guessing bits of the secret key to a random guess.
While secret encryption keys are commonly-used for securing wireless transmissions, establishment of such keys has traditionally been accomplished using computational techniques at the higher layers of the wireless communication protocol stack. However, the multipath electromagnetic propagation typical of many environments can also be an excellent source of random variables useful for encryption key generation. Furthermore, antennas play an important role in how the transmitter and receiver excite or sense the channel and therefore become a critical component in the performance of techniques that exploit the multipath channel for key establishment. This paper focuses on how using multiple antennas can dramatically improve the performance of such key establishment methods.
There is a growing interest in physical layer security. Recent work has demonstrated that wireless devices can generate a shared secret key by exploiting variations in their channel. The rate at which the secret bits are generated, however, depends heavily on how fast the channel changes. As a result, existing schemes have a low secrecy rate and are mainly applicable to mobile environments. In contrast, this paper presents a new physical-layer approach to secret key generation that is both fast and independent of channel variations. Our approach makes a receiver jam the signal in a manner that still allows it to decode the data, yet prevents other nodes from decoding. Results from a testbed implementation show that our method is significantly faster and more accurate than state of the art physical-layer secret key generation protocols. Specifically, while past work generates up to 44 secret bits/s with a 4% bit disagreement between the two devices, our design has a secrecy rate of 3-18 Kb/s with 0% bit disagreement.
Internet-of-Things (IoT) networks generally contain resource-constrained devices that require an energy-efficient key generation procedure to producing secure keys at a faster rate. The physical characteristics of the wireless channel can be exploited to secure communication within IoT networks. In particular, secret keys can be generated by leveraging on the randomness of the wireless physical channel between two communicating parties. The conventional mechanism of generating keys at the physical layer, i.e., using channel probing, quantization, information reconciliation, and privacy amplification, may not be preferable for IoT devices. In addition, in some cases IoT devices may be deployed in static environments, wherein the channel coherence time is too high to generate keys at a faster rate and with the desired randomness. This study proposes a mapping table-based key distribution scheme for IoT environments, wherein multiple characteristics of the random channel are combined to improve not only the key generation rate (KGR) but also the key agreement rate (KAR) and bit error rate (BER). In the proposed scheme, both the channel magnitude and the phase are exploited in the key generation process. The proposed scheme is immune to channel estimation errors while providing sufficient randomness in the static environment. Additionally, the scheme is thoroughly investigated for different scenarios including the case of a smarter eavesdropper, which attempts to estimate the channel between the legitimate nodes. This case verifies the robustness of the proposed scheme in different settings and attack models.
In this paper, we propose a novel approach for providing secure wireless communications in transmit-receive diversity systems. In this approach, we precode the information-bearing signal with a uniquely generated randomized eigenvector-based jamming signal to impair the eavesdropper's received signal, while the main channel, the link between the transmitter and the desired receiver, remains unaffected. Unlike existing methods, our approach can be applied to any antenna array configuration, even when the receiver and eavesdropper utilize more antennas than the transmitter, with no benefits to the eavesdropper's information detection capability from employing more antenna elements. Moreover, our proposed approach can provide more degrees of freedom for the jamming signal, significantly increasing the provided level of security. Additionally, our scheme does not assume any knowledge about the eavesdropper or even the number of collaborating eavesdroppers. Our simulation results show a secrecy capacity increase of about 7 bits/s/Hz for a 4 x 4 antenna configuration under typical transmit power constraints, which results in significant improvement in security performance and enables physically secure wireless communications.