  Biometric-based authentication is gaining increasing attention for wearables
and mobile applications. Meanwhile, the growing adoption of sensors in
wearables also provides opportunities to capture novel wearable biometrics. In
this work, we propose EarDynamic, an ear canal deformation-based user
authentication using in-ear wearables. EarDynamic provides continuous and
passive user authentication and is transparent to users. It leverages ear canal
deformation that combines the unique static geometry and dynamic motions of the
ear canal when the user is speaking for authentication. It utilizes an acoustic
sensing approach to capture the ear canal deformation with the built-in
microphone and speaker of the in-ear wearable. Specifically, it first emits
well-designed inaudible beep signals and records the reflected signals from the
ear canal. It then analyzes the reflected signals and extracts fine-grained
acoustic features that correspond to the ear canal deformation for user
authentication. Our extensive experimental evaluation shows that EarDynamic can
achieve a recall of 97.38% and an F1 score of 96.84%. Results also show that
our system works well under different noisy environments with various daily
activities.
