Earables, or ear wearables, are increasingly being used for a variety of personal applications, prompting the development of authentication schemes to safeguard user privacy. Existing authentications are designed for traditional in-ear earphones, relying on a closed ear canal environment, which is not suited for bone conduction earphones that feature an open-ear design. In this paper, we propose HCR-Auth, a new authentication approach for bone conduction earphones based on head biometrics. It employs a modulated chirp signal, emitted by the earphone speaker, to actively sense the user's head structure, and captures the response through the earphone's accelerometer. It operates implicitly, eliminating additional efforts from the user to perform authentication. Through extensive experiments involving 60 subjects, we determine that HCR-Auth achieves a commendable balanced accuracy of 96.55% using only 10 registration samples, proving its efficacy and resilience against potential threats. Our dataset and source codes are available at https://anonymous.4open.science/r/HCR-Auth-D43B/.

HCR-Auth: Reliable Bone Conduction Earphone Authentication with Head Contact Response