Biometric data stored in automated recognition systems are at risk of attacks. This is particularly true for large-scale biometric identification systems, where the reference database is often accessed remotely. A popular approach for the protection of the stored templates is homomorphic encryption, which grants privacy protection while maintaining the biometric performance of the unprotected system. However, it introduces a significant computational overhead that can render identification transactions infeasible. To reduce this workload, biometric indexing in the encrypted domain has become a recent research interest. In this work, we show that in such schemes, auxiliary indexing data can leak additional privacy-sensitive information that violate standardized requirements for biometric template protection. In response to this leakage, we propose a novel framework HEBI that protects biometric indexing approaches at a post-quantum security level while requiring a computational effort of only 0.12 milliseconds per cluster.

Contactless fingerprint recognition is an emerging biometric technology and Presentation Attack Detection (PAD) methods are crucial to preserve system security. Convolutional Neural Networks (CNNs) represent the state-of the-art of PAD algorithms for many contactless captured biometric characteristics and various research groups proposed specialized CNN-based PAD methods or used general purpose CNNs to detect Presentation Attacks (PAs). In this work, we compare nine CNN-based PAD methods for contactless fingerprint PAD: five general purpose algorithms, and four dedicated PAD methods designed for various biometric characteristics. To achieve this, we combine the COLFISPOOF database with three bona fide databases: the HDA database and both versions of the ISPFD database. We set up our experiments using a baseline evaluation protocol and four Leave-One-Out (LOO) protocols, to benchmark the generalization capabilities to unseen data. The results reported by using the Attack Presentation Classification Error Rate (APCER) vs. Bona fide Presentation Classification Error Rate (BPCER) and the Detection Equal Error Rate (D-EER). Further, we discuss the achieved results in detail and give recommendations for real-world implementations. Our results show that established PAD algorithms for other biometric characteristics can accurately detect PAs on contactless fingerprints. While strong deviations between the considered PAD algorithms are observed, the best performing method shows a D-EER between 0.01% and 0.08% (depending on the LOO partition) and a APCER of 0.00% at a BPCER of 1.00%.

Protecting minutiae-based fingerprint templates with fully homomorphic encryption has recently been recognised as a hard problem. In this work, we evaluate state-of-the-art fingerprint recognition based on minutiae templates using post-quantum secure fully homomorphic encryption that operates directly on floating point numbers, such that no simplification or quantisation of the comparison algorithm is necessary. In a practical evaluation on a publicly available dataset, we run a benchmark and provide directions for future work.

The efficiency of biometric systems, in particular efficient and accurate biometric identification, is one of the most challenging open problems in biometrics today. Adding to that, biometric data are sensitive data deserving adequate protection. As a solution, this work proposes an efficient privacy-preserving reduction of the computational workload of biometric identification systems using public-key encryption with keyword search (PEKS). For long-term protection of the biometric data, fully homomorphic encryption is applied for template protection. As all applied cryptographic schemes are lattice-based, they also offer post-quantum security. Throughout the system, the recognition accuracy of the unprotected system is preserved. In an evaluation on a public face database, the computational workload of an identification search in the encrypted domain is reduced down to 8.4% compared to an exhaustive search, achieving identification on 1062 subjects in 210 milliseconds. Based on these results, an identification search on 1 million subjects can be estimated at under 3 minutes using off-the-shelf hardware.

Due to the wide operational deployment of biometric recognition systems, presentation attacks targeting the capture device have become a severe threat. Especially for fingerprint recognition, a high number of different materials allows the creation of numerous presentation attack instruments (PAIs) in the form of full fake fingers and fingerprint overlays, which very much resemble the skin properties at fingertips. As a consequence, automated presentation attack detection (PAD) mechanisms are of utmost importance. Utilising a 1310 nm laser in a new capture device, we present an evaluation of three long short-term memory (LSTM) networks in comparison to eight convolutional neural networks (CNNs) on a database comprising over 22,000 samples and including 45 different PAI species. The LSTMs analyse temporal properties within a captured sequence in order to detect blood movement, while the CNNs take into account spatial properties within a single frame to focus on reflections by the PAI material. The results show that the diversity of PAI species is too big for a single classifier to correctly detect all presentation attacks. However, by fusing the scores from distinct algorithms, we can achieve a detection accuracy of 3.71% APCER for a convenient BPCER of 0.2%.

Speech recordings are a rich source of personal, sensitive data that can be used to support a plethora of diverse applications, from health profiling to biometric recognition. It is therefore essential that speech recordings are adequately protected so that they cannot be misused. Such protection, in the form of privacy-preserving technologies, is required to ensure that: (i) the biometric profiles of a given individual (e.g., across different biometric service operators) are unlinkable; (ii) leaked, encrypted biometric information is irreversible, and that (iii) biometric references are renewable. Whereas many privacy-preserving technologies have been developed for other biometric characteristics, very few solutions have been proposed to protect privacy in the case of speech signals. Despite privacy preservation this is now being mandated by recent European and international data protection regulations. With the aim of fostering progress and collaboration between researchers in the speech, biometrics and applied cryptography communities, this survey article provides an introduction to the field, starting with a legal perspective on privacy preservation in the case of speech data. It then establishes the requirements for effective privacy preservation, reviews generic cryptography-based solutions, followed by specific techniques that are applicable to speaker characterisation (biometric applications) and speech characterisation (non-biometric applications). Glancing at non-biometrics, methods are presented to avoid function creep, preventing the exploitation of biometric information, e.g., to single out an identity in speech-assisted health care via speaker characterisation. In promoting harmonised research, the article also outlines common, empirical evaluation metrics for the assessment of privacy-preserving technologies for speech data.