New security definitions for biometric authentication with template protection: Toward covering more threats against authentication systems

Existing studies on the security of biometric authentication with template protection have considered the adversaries who obtain only protected templates. Since biometric authentication systems transmit data other than the protected templates, we need to consider how to secure biometric authentication systems against adversaries with those data. In this paper, we propose a classification of adversaries in biometric authentication with template protection into the following three types in accordance with their knowledge: (1) protected template data, (2) data transmitted during authentication, and (3) both types of data. We also propose a new security metric unforgeability, which provides authentication security against attacks by adversaries impersonating someone else on authentication systems even when they cannot obtain the biometric information of a claimant. We then give security definitions against each type of adversary we classified. We also propose a biometric authentication scheme with template protection that is irreversible against all types of adversaries.