Small-angle approximation attack on angle-based many-to-one functions for biometric templates

If a biometric template is compromised, the invasion of user privacy is inevitable. Since human biometric is irreplaceable and irrevocable, such an invasion implies a permanent loss of user identity. As a result, many transformation methods are proposed to convert the biometric template into non-invertible version of itself. However, if the transformation functions are not carefully designed, the “non-invertible” templates are susceptible to be partially or fully invertible. In this paper, we proposed a template inversion technique, namely small-angle approximation attack, which is less studied in the literature. We reveal that the angle-based many-to-one property of the non-linear functions is highly vulnerable to small-angle approximation attack.