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Cryptographic-biometric authentication systems using biometric template protection schemes

Authentication systems are an important application area for biometrics. The method successfully used in classic password authentication systems of storing a hashed password value, which ensures the password remains secure, is excluded here, however, because two recordings of the biometric feature never match completely.

Current research is therefore addressing the question of how the advantages of biometrics can be effectively combined with reliable cryptographic procedures so that the original biometric feature can no longer be stored in plain text but as a public reference data record, in a similar way to the password procedure. By means of biometric template protection, a public data record is created that enables both the identification and the verification of an individual, provided that enquirer can evidence knowledge of the biometric template. Without evidence of the biometric template, the database does not reveal any information about the person.

An important aspect to consider when designing and implementing biometric systems is protecting the stored biometric reference information. The standard "ISO/IEC 24745 – Information technology – Security techniques – Biometric information protection" lists several methods for biometric template protection. Biometric encryption – also known as biometric cryptosystems – is an important class of methods, which aims at protecting the biometric reference information without the need to store secret information such as cryptographic keys. Biometric encryption enables biometric authentication using reference data that does not reveal the original biometric information.

An overview of the state of the art in biometric template protection is provided in the final project report of "BioKeyS Pilot-DB Teil II". This report also includes a summary of the standardisation activities in this field – namely ISO/IEC 24745 – and the framework that was contributed to this standard by the European Integrated Project TURBINE.

Report: Projekt BioKeyS-Pilot-DB Teil II, Abschlussbericht

Publication:

Biometric encryption based on genetic fingerprints

The first project of the BioKeyS project series provided details of a biometric cryptosystem using genetic fingerprints. A detailed security analysis was presented for this procedure based on the entropy of the DNA (deoxyribonucleic acid) data and formal security results on the underlying Fuzzy Commitment Scheme. The resulting scheme was shown to be robust and efficient by analysing the typical frequency and structure of errors in DNA measurements and selecting appropriate error correcting codes. As a result, a security level was obtained equivalent to cryptographic keys with 73 bits and a False Reject Rate (FRR) well below 1%.
The project BioKeyS-DNA was initiated by the BSI and accomplished by an interdisciplinary group consisting of:

  • Federal Office for Information Security (BSI), 53175 Bonn, Germany
  • Giesecke & Devrient GmbH, 81677 Munich, Germany
  • Institute of Medical Informatics and Statistics, Christian-Albrecht University of Kiel, 24105 Kiel, Germany
  • Institute of Experimental Mathematics, University of Duisburg-Essen, 45326 Essen, Germany
  • Labor Dr. Krone & Partner, D-32105 Bad Salzuflen, Germany
  • secunet Security Networks AG, 45128 Essen, Germany

The following report concludes this project: A cryptographic biometric authentication system based on genetic fingerprints

Publication (shortened version):

  • U. Korte, M. Krawczak, U. Martini, J. Merkle, M. Niesing, R. Plaga, C. Tiemann, and H. Vinck: "A cryptographic biometric authentication system based on genetic fingerprints", in Proceedings of Sicherheit 2008: Sicherheit, Schutz und Zuverlässigkeit. Lecture Notes in Informatics (LNI), © German Informatics Society (GI), P-128, ISBN 978-3-88579-222-2, pp. 263-276, 2008.

Implementation of a Fuzzy Vault Scheme for Fingerprints

The evaluation and practical implementation of one Template Protection Procedure – the Fuzzy Vault – was the main objective of the project BioKeyS-Multi. To achieve this, a biometric cryptosystem for fingerprints of multiple fingers was introduced that combines two approaches: the Fuzzy Vault links the fingerprint templates with a secret polynomial and conceals it in an appropriately large set of random points (chaff points), and uses a special fingerprint comparison algorithm for additional error correction. To enhance the entropy of the biometric information, fingerprints of multiple fingers of one person were used.

The security capacity of this scheme was investigated as part of the BioKeyS-Multi project. A reference implementation was developed in parallel to investigate the feasibility.

The project BioKeyS-Multi was initiated by the BSI and accomplished by an interdisciplinary group consisting of:

  • Federal Office for Information Security (BSI), 53175 Bonn, Germany
  • secunet Security Networks AG, 45128 Essen, Germany

Report: Projekt BioKeyS-Multi: Implementierung eines Fuzzy Fingerprint Vault Version 1.1.1, 03.09.2009

Publication:

Improvement of the Fuzzy Vault Fingerprint Procedure

The results of the project BioKeyS-Multi revealed several approaches for potential optimisations. These were investigated in the follow-up project BioKeyS-Pilot-DB I.
It was demonstrated that minutia quality filtering and enforcing a minimum number of minutia per finger in the template significantly increases recognition performance. Both optimisation approaches are very sensitive to the respective thresholds, which must be carefully set on the basis of empirical data.
Although it was not possible to achieve recognition rates required to prove the security by information-theoretic arguments, a security level against existing attacks of 80 bit for three fingers and of 100 bit for four fingers was obtained.

Enrolment and verification simulations indicated that this optimised scheme can be effective and efficient in practice. The process of capturing several fingers can be made easier using multi-finger sensors. Nevertheless, the parameters need to be selected with care to reduce the error rates and effort for enrolment.

The project BioKeyS-Pilot-DB I was initiated by the BSI and accomplished by an interdisciplinary group consisting of:

  • Federal Office for Information Security (BSI), 53175 Bonn, Germany
  • secunet Security Networks AG, 45128 Essen, Germany

Report: Projekt BioKeyS-PilotDB-Teil 1 Projektbericht, Version 1.1.1, 27.04.2010

Publications:

Template Protection Schemes linked with Password Authentication and Investigation of Identification Scenarios

The recognition and security performance of Biometric Template Protection Procedures is limited by the entropy of biometric data, while in knowledge-based authentication it is hard for users to remember long secure passwords. Thus, the project BioKeyS-Pilot-DB II, combined the Fuzzy Vault Fingerprint system with additional information (PIN, Passwords) to improve both, security and recognition performance.
In addition, the project investigated identification scenarios and the specific challenges that occur when using template protection procedures for identification. Thus, in an interdisciplinary approach, techniques were researched that pave the way for a fast database search over a set of protected templates. Various techniques were implemented and benchmarked on the publicly available database NIST SD14.
Finally, the project investigated the impact of the quality of minutia extraction methods, which have considerable impact on the performance and security of minutia-based template protection schemes (including the Fuzzy Vault scheme for fingerprints). For this purpose, a semantic conformance testing methodology was applied to a test dataset compiled from NIST Special Databases NISTSD14 and NIST SD29 for which dactyloscopic ground truth data (i.e. minutiae data determined by human experts) were available. The results obtained were presented at the NIST International Biometric Performance Conference (IBPC 2010).

The project BioKeyS-Pilot-DB Teil II was a research project of the BSI and accomplished by an interdisciplinary group consisting of:

  • Federal Office for Information Security (BSI), 53175 Bonn, Germany
  • Darmstadt University of Applied Sciences (HDA), Darmstadt, Germany
  • Fraunhofer Institute for Computer Graphics Research (IGD), Darmstadt, Germany
  • RWTH Aachen University, Aachen, Germany
  • Ludwig Maximilian University of Munich (LMU), Munich, Germany
  • secunet Security Networks AG, Essen, Germany

Report: Projekt BioKeyS-Pilot-DB Teil II, Abschlussbericht

Publications:

Privacy and Accuracy of Fingerprint Recognition Based on the Fuzzy Commitment Procedure

Biometric cryptosystems have been developed and reached a level of sophistication that has enabled commercial products to become available. Among the most promising examples are designs based on a cryptographic technique known as fuzzy commitment scheme. The aim of the project BioKeyS-Pilot-DB III was to assess the achievable level of privacy and accuracy of biometric cryptosystems for fingerprints based on the fuzzy commitment scheme.

The project first defined a general framework for the assessment of the privacy of biometric cryptosystems, which was published in a paper "A Reference Framework for the Privacy Assessment of Biometric Encryption Systems" at the BIOSIG 2010 Conference.
Furthermore, approaches for the fusion of several fingers per subject were investigated in the context of biometric cryptosystems and a new fusion method was presented, which preserves the confidentiality of templates and is easy to implement.

Based on the developed framework for privacy assessment and traditional methods for determining the recognition accuracy of biometric solutions, the project assessed the potential of biometric cryptosystems for fingerprints based on the fuzzy commitment scheme considering a commercial product as an example implementation. This analysis was based on heuristic arguments and a thorough discussion of possible attacks as well as on empirical evaluations on public and proprietary databases.

The project BioKeyS-Pilot-DB III was initiated by the BSI and accomplished by an interdisciplinary group consisting of:

  • Federal Office for Information Security (BSI), 53175 Bonn, Germany
  • priv-ID B.V., Eindhoven, Netherlands
  • secunet Security Networks AG, 45128 Essen, Germany

Report: Study of the Privacy and Accuracy the Fuzzy Commitment Scheme, BioKeyS III Final Report, Version 2.0

Publication:

BioKeyS-KBEinweg: Development and Testing of One-way Crypto-biometric Functions

In biometric systems, the stored reference data comprise unique characteristics of a data subject, which can contain sensitive data (i.e., ethnicity, diseases). If the reference data is compromised, biometric characteristics cannot be easily cancelled or replaced. Furthermore, the number of biometric characteristics a single person has is limited. This means it is critical for biometrics to be used in a way that complies with data protection to provide sufficient protection to the biometric reference data.

Biometric cryptographic "template protection" schemes ensure that the biometric information cannot be formed again from the reference data. These technologies enable inherently secure biometric authentication and therefore a new simplified application of biometrics.

The aim of this project is to carry out a study on biometric cryptographic one-way functions for minutiae-based fingerprints based on the promising fuzzy vault approach, including a solution to the following two challenges that still currently exist:

  • Fingerprints must be aligned. Until now, additional information has often been used to achieve this, but it may reveal information about the actual biometric feature.
  • Multiple use of biometric characteristics in different applications based on the fuzzy vault scheme can also lead to what is referred to as cross-matching problems if these applications are linked with each other.

The BioKeyS-KBEinweg project consists of three main focus areas:

  1. In the first work package (WP1), a configurable fuzzy vault test bench is developed and supplied.
  2. In the second work package (WP2), a fuzzy vault structure for minutiae-based fingerprints is presented that provides a solution to the two challenges mentioned previously by fully pre-aligning the fingerprints and then quantising the minutiae positions on a grid, whereby the grid points not occupied by minutiae are additionally included in the fuzzy vault as chaff points. In addition, the recognition performance is improved by including the minutiae angles and the minutiae types. This approach will be evaluated experimentally using the publicly available MCYT-100 database.
  3. In the third work package (WP3), different rotation and translation invariant characteristics are presented and quantised as protection against cross-matching attacks and subsequently consolidated. Experimental tests are carried out using the publicly available MCYT-100 database for three different feature-level fusions.

The project BioKeyS-KBEinweg was initiated by the BSI as the project owner and accomplished by an interdisciplinary group consisting of:

  • Federal Office for Information Security (BSI), 53175 Bonn, Germany
  • Darmstadt University of Applied Sciences (Project Management)
  • secunet Security Networks AG, 45128 Essen, Germany
  • Georg August University of Göttingen, Germany
  • Fraunhofer Institute for Computer Graphics Research (IGD), Germany

Report: BioKeyS-KBEinweg

Publications:

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