Reconstructing Protected Biometric Templates from Binary Authentication Results

TL;DR

This paper demonstrates that biometric templates can be reconstructed solely from binary authentication success/failure signals, revealing significant privacy vulnerabilities even in protected biometric systems.

Contribution

The authors introduce a novel attack method that reconstructs biometric templates from binary success/failure data, exposing vulnerabilities in existing biometric protection schemes.

Findings

Reconstructed facial images pass the system over 98% of the time

Negligible loss in template reconstruction accuracy

Applicable to systems with similar binary output mechanisms

Abstract

Biometric data is considered to be very private and highly sensitive. As such, many methods for biometric template protection were considered over the years -- from biohashing and specially crafted feature extraction procedures, to the use of cryptographic solutions such as Fuzzy Commitments or the use of Fully Homomorphic Encryption (FHE). A key question that arises is how much protection these solutions can offer when the adversary can inject samples, and observe the outputs of the system. While for systems that return the similarity score, one can use attacks such as hill-climbing, for systems where the adversary can only learn whether the authentication attempt was successful, this question remained open. In this paper, we show that it is indeed possible to reconstruct the biometric template by just observing the success/failure of the authentication attempt (given the ability to inject a sufficient amount of templates). Our attack achieves negligible template reconstruction loss and enables full recovery of facial images through a generative inversion method, forming a pipeline from binary scores to high-resolution facial images that successfully pass the system more than 98\% of the time. Our results, of course, are applicable for any protection mechanism that maintains the accuracy of the recognition.