EarPPG: Securing Your Identity with Your Ears

Wearable devices have become indispensable gadgets in people's daily lives nowadays; especially wireless earphones have experienced unprecedented growth in recent years, which lead to increasing interest and explorations of user authentication techniques. Conventional user authentication methods embedded in wireless earphones that use microphones or other modalities are vulnerable to environmental factors, such as loud noises or occlusions. To address this limitation, we introduce EarPPG, a new biometric modality that takes advantage of the unique in-ear photoplethysmography (PPG) signals, altered by a user's unique speaking behaviors. When the user is speaking, muscle movements cause changes in the blood vessel geometry, inducing unique PPG signal variations. As speaking behaviors and PPG signals are unique, the EarPPG combines both biometric traits and presents a secure and obscure authentication solution. The system first detects and segments EarPPG signals and proceeds to extract effective features to construct a user authentication model with the 1D ReGRU network. We conducted comprehensive real-world evaluations with 25 human participants and achieved 94.84% accuracy, 0.95 precision, recall, and f1-score, respectively. Moreover, considering the practical implications, we conducted several extensive in-the-wild experiments, including body motions, occlusions, lighting, and permanence. Overall outcomes of this study possess the potential to be embedded in future smart earable devices.