RF-Parrot: Wireless Eavesdropping on Wired Audio

Recent works demonstrated that we can eavesdrop on audio by using radio frequency signals or videos to capture the physical surface vibrations of surrounding objects. They fall short when it comes to intercepting internally transmitted audio through wires. In this work, we first address this gap by proposing a new eavesdropping system, RF-Parrot, that can wirelessly capture the audio signal transmitted in earphone wires.

Our system involves embedding a tiny field-effect transistor in the wire to create a battery-free retroreflector, with its reflective efficiency tied to the audio signal's amplitude. To capture full details of the analog audio signals, we engineered a novel retroreflector using a depletion-mode MOSFET, which can be activated by any voltage of the audio signals, ensuring no information loss. We also developed a theoretical model to demystify the nonlinear transmission of the retroreflector, identifying it as a convolution operation on the audio spectrum. Subsequently, we have designed a novel convolutional neural network-based model to accurately reconstruct the original audio. Our extensive experimental results demonstrate that the reconstructed audio bears a strong resemblance to the original audio, achieving an impressive 95% accuracy in speech command recognition.