Towards a General Framework for Privacy-Preserving Unimodal and Multimodal Biometric Verification

Towards a General Framework for Privacy-Preserving Unimodal and Multimodal Biometric Verification


Beneficiary: Marta Gomez-Barrero, PhD Student at ATVS, Universidad Autonoma de Madrid, Spain

Host: Prof. Dr. Christoph Busch, NISlab, Norwegian University of Science and Technology (NTNU), Gjovik, Norway

Period: 04/01/2016 – 15/02/2016


Purpose of the STSM


Even though biometric recognition systems are nowadays widely deployed, many concerns arise from the privacy issues posed by biometric data storage.  Among the various schemes proposed in the literature, Bloom filter based template protection has been successfully applied to different biometric traits (iris, face, fingerprint, and fingervein in a past STSM) granting irreversibility while preserving verification accuracy.

However, the application of this protection scheme to a given biometric characteristic is not straightforward – appropriate values for its parameters have to be computed ad hoc. Moreover, so far a multi-biometric approach has been only proposed for protected templates having the same size.

In the present Short Time Scientific Mission (STSM), we have continued our shared research line based on template protection to devise a new general framework for the estimation of the Bloom filter parameters based on statistical measures of the unprotected templates. Furthermore, we have proposed a new multi-biometrics approach for templates of different sizes based on a weighted feature-level fusion. The soundness of both methods has been analysed for several characteristics, namely: face, iris, fingerprint and fingervein.


Work carried out during the STSM


  1. Development of a methodology to reliably estimate the main parameters of Bloom filter based template protection schemes.
  2. Development of a general multi-biometric template protection system based on Bloom filters and a weighted feature level fusion.
  3. Evaluation of the proposed methodologies on several biometric characteristics – face, iris, fingerprint and fingervein – and feature level fusion – face and iris.


Results of the STSM


A new framework has been proposed for the estimation of the two main parameters of Bloom filter based schemes, based on a statistical analysis of the unprotected binary templates. A balance is reached between the irreversibility provided and accuracy degradation.

For the validation of the proposed framework, we use two independent sets of databases to avoid biased results. First, appropriate values for the system parameters are estimated on the development databases. Then, the performance of the protected systems is compared to that of the unprotected systems, evaluated on the test database. Comparing the evaluation results in terms of the Detection Error Trade-Off (DET) curves, we observe that accuracy is preserved for all characteristics considered.

Finally, the performance of the multi-biometric approach is compared to a score level unprotected fusion, achieving a higher accuracy. As a consequence, we may conclude that we achieve: i) higher verification accuracy and ii) more secure and privacy protected templates, due to the feature level fusion carried out in the protected domain.


Future Collaboration


As shared future research lines, we could highlight the continuation of the combination of the Bloom filter based template protection scheme with another protection approach based on honey templates, developed at the NISlab, which further protects the privacy of the subject. An article has been submitted with the first analysis and results.

Additionally, we are currently preparing a manuscript to report the results achieved during the STSM.

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