Variable-length template protection based on homomorphic encryption with application to signature biometrics

Any privacy leakage of biometric data poses severe security risks given their sensitive nature. Biometric templates should thus be protected, storing irreversibly transformed or encrypted biometric signals, while preserving the unprotected system's performance. Based on the recent developments by Zhu et al. on privacy preserving similarity evaluation of time series data, we present a new biometric template protection scheme based on homomorphic probabilistic encryption, where only encrypted data is stored or exchanged. We then apply the proposed scheme to signature verification and show that all requirements described in the ISO/IEC 24745 standard are met with no performance degradation, using a publicly available database and a free implementation of the Paillier cryptosystem. Moreover, the proposed approach is robust to hill-climbing attacks.