MagEar
Qianru Liao, Yongzhi Huang, Yandao Huang, Yuheng Zhong, Huitong Jin, Kaishun Wu
Abstract
Speakers have been widely embedded in various electronic devices as a standard configuration. The security vulnerability of microspeakers (such as earphones) is commonly overlooked because it is often assumed that soundproof boundaries, such as walls, can prevent privacy-infringing sound leakage. In this paper, we present the prototype MagEar, an eavesdropping system that leverages magnetic side-channel signals leaked by a microspeaker to recover intelligible human speech. MagEar has sufficiently high sensitivity to detect magnetic fields on the order of nanotesla, exceeding some high-precision magnetometers. It can recover high-quality audio with 90% similarity to the original audio even at a distance of 60 cm. In addition, the MagEar prototype is portable and can be hidden in a headset shell. We have implemented MagEar as a proof-of-concept system and conducted several case studies of eavesdropping on different types of speaker-embedded devices, including earphones, and we have demonstrated the ability to successfully transcribe the recovered speech using automatic speech recognition techniques even when blocked by soundproof walls. We hope that our work can push manufacturers to rethink this security vulnerability of speakers.