Convolution Attack on Frequency-Hopping by Full-Duplex Radios

TL;DR

This paper introduces a novel real-time adversarial attack on frequency-hopping wireless systems using full-duplex radios, significantly impacting channel characteristics and challenging existing detection methods, with proposed countermeasures involving advanced modulation and secret-key strategies.

Contribution

The paper presents the first practical attack that modifies signals within symbol periods to induce rapid fading, and explores new mitigation techniques for frequency-hopping systems.

Findings

Eve's attack converts slow-fading channels to rapid-fading ones.

Large antenna arrays are needed for reliable detection with OOK.

Secret-key randomization enhances BFSK robustness.

Abstract

We propose a new adversarial attack on frequency-hopping based wireless communication between two users, namely Alice and Bob. In this attack, the adversary, referred to as Eve, instantaneously modifies the transmitted signal by Alice before forwarding it to Bob within the symbol-period. We show that this attack forces Bob to incorporate Eve's signal in the decoding process; otherwise, treating it as noise would further degrade the performance akin to jamming. Through this attack, we show that Eve can convert a slow-fading channel between Alice and Bob to a rapid-fading one by modifying every transmitted symbol independently. As a result, neither pilot-assisted coherent detection techniques nor blind-detection methods are directly applicable as countermeasures. As potential mitigation strategies, we explore the applicability of frequency-hopping along with (i) On-Off keying (OOK) and (ii) Binary Frequency-Shift-Keying (FSK) as modulation schemes. In the case of OOK, the attacker attempts to introduce deep-fades on the tone carrying the information bit, whereas in the case of BFSK, the attacker pours comparable energy levels on the tones carrying bit-$0$ and bit-$1$, thereby degrading the performance. Based on extensive analyses and experimental results, we show that (i) when using OOK, Bob must be equipped with a large number of receive antennas to reliably detect Alice's signal, and (ii) when using BFSK, Alice and Bob must agree upon a secret-key to randomize the location of the tones carrying the bits, in addition to randomizing the carrier-frequency of communication.