A Survey on Multimodal Biometrics and the Protection of Their Templates <s> Combination of Cryptography and Multimodalities <s> Within the next year, travelers from dozens of nations may be carrying a new form of passport in response to a mandate by the United States government. The e-passport, as it is sometimes called, represents a bold initiative in the deployment of two new technologies: Radio-Frequency Identification (RFID) and biometrics. Important in their own right, e-passports are also the harbinger of a wave of next-generation ID cards: several national governments plan to deploy identity cards integrating RFID and biometrics for domestic use. We explore the privacy and security implications of this impending worldwide experiment in next-generation authentication technology. We describe privacy and security issues that apply to e-passports, then analyze these issues in the context of the International Civil Aviation Organization (ICAO) standard for e-passports. <s> BIB001 </s> A Survey on Multimodal Biometrics and the Protection of Their Templates <s> Combination of Cryptography and Multimodalities <s> We propose the first practical and secure way to integrate the iris biometric into cryptographic applications. A repeatable binary string, which we call a biometric key, is generated reliably from genuine iris codes. A well-known difficulty has been how to cope with the 10 to 20 percent of error bits within an iris code and derive an error-free key. To solve this problem, we carefully studied the error patterns within iris codes and devised a two-layer error correction technique that combines Hadamard and Reed-Solomon codes. The key is generated from a subject's iris image with the aid of auxiliary error-correction data, which do not reveal the key and can be saved in a tamper-resistant token, such as a smart card. The reproduction of the key depends on two factors: the iris biometric and the token. The attacker has to procure both of them to compromise the key. We evaluated our technique using iris samples from 70 different eyes, with 10 samples from each eye. We found that an error-free key can be reproduced reliably from genuine iris codes with a 99.5 percent success rate. We can generate up to 140 bits of biometric key, more than enough for 128-bit AES. The extraction of a repeatable binary string from biometrics opens new possible applications, where a strong binding is required between a person and cryptographic operations. For example, it is possible to identify individuals without maintaining a central database of biometric templates, to which privacy objections-might be raised <s> BIB002 </s> A Survey on Multimodal Biometrics and the Protection of Their Templates <s> Combination of Cryptography and Multimodalities <s> Biometric recognition offers a reliable solution to the problem of user authentication in identity management systems. With the widespread deployment of biometric systems in various applications, there are increasing concerns about the security and privacy of biometric technology. Public acceptance of biometrics technology will depend on the ability of system designers to demonstrate that these systems are robust, have low error rates, and are tamper proof. We present a high-level categorization of the various vulnerabilities of a biometric system and discuss countermeasures that have been proposed to address these vulnerabilities. In particular, we focus on biometric template security which is an important issue because, unlike passwords and tokens, compromised biometric templates cannot be revoked and reissued. Protecting the template is a challenging task due to intrauser variability in the acquired biometric traits. We present an overview of various biometric template protection schemes and discuss their advantages and limitations in terms of security, revocability, and impact on matching accuracy. A template protection scheme with provable security and acceptable recognition performance has thus far remained elusive. Development of such a scheme is crucial as biometric systems are beginning to proliferate into the core physical and information infrastructure of our society. <s> BIB003 </s> A Survey on Multimodal Biometrics and the Protection of Their Templates <s> Combination of Cryptography and Multimodalities <s> Random projection provides a good diversification effect for biometric template protection but is drawing increasing security concerns under the token-stolen (or public parameter) case. We propose a dynamic random projection method to alleviate these security concerns due to the stolen token by increasing the computational complexity to search for the unprotected biometric features. This is achieved by a projection process which dynamically assembles a random projection matrix from a set of candidate projection vectors. The selection of projection vectors is decided by the biometric feature vector itself and thus forms a nonlinear projection process. The proposed method permits the public and secure storage of all the candidate random vectors without the need for external secret keys. Experiments on the 800 samples in the database FVC2002DB2_A demonstrate the well-kept biometrie performance of the proposed method. <s> BIB004 </s> A Survey on Multimodal Biometrics and the Protection of Their Templates <s> Combination of Cryptography and Multimodalities <s> Fuzzy commitment schemes have been established as a reliable means of binding cryptographic keys to binary feature vectors extracted from diverse biometric modalities. In addition, attempts have been made to extend fuzzy commitment schemes to incorporate multiple biometric feature vectors. Within these schemes potential improvements through feature level fusion are commonly neglected. In this paper a feature level fusion technique for fuzzy commitment schemes is presented. The proposed reliability-balanced feature level fusion is designed to re-arrange and combine two binary biometric templates in a way that error correction capacities are exploited more effectively within a fuzzy commitment scheme yielding improvement with respect to key-retrieval rates. In experiments, which are carried out on iris-biometric data, reliability-balanced feature level fusion significantly outperforms conventional approaches to multi-biometric fuzzy commitment schemes confirming the soundness of the proposed technique. <s> BIB005 </s> A Survey on Multimodal Biometrics and the Protection of Their Templates <s> Combination of Cryptography and Multimodalities <s> The term biometrics refers to “automated recognition of individuals based on their behavioral and biological characteristics” (ISO/IEC JTC1 SC37). Several physiological (static) as well as behavioral (non-static) biometric characteristics have been exploited (Jain, Flynn & Ross, 2008) such as fingerprints, iris, face, hand, voice, gait, keystroke dynamics, etc., depending on distinct types of applications (see Figure 1). Biometric traits are acquired applying adequate sensors and distinctive feature extractors are utilized in order to generate a biometric template (reference data) in the enrollment process. During verification (authentication process) or identification (identification can be handled as a sequence of biometric comparisons against the enrollment records in a reference databse) the system processes another biometric measurement from which an according template is extracted and compared against the stored template(s) yielding acceptance/ rejection or hit/ no-hit, respectively. The presented work is motivated by very recent advances in the fields of multi-biometric recognition (Ross et al., 2006) and biometric template protection (Rathgeb & Uhl, 2011). Automatic recognition systems based on a single biometric indicator often have to contend with unacceptable error rates (Ross & Jain, 2003). Multi-biometric systems have improved the accuracy and reliability of biometric systems (Ross et al., 2006). Biometric vendors are already deploying multi-biometric systems (e.g. fingerprint and finger vein by SAFRAN Morpho1) and multi-biometric recognition is performed on large-scale datasets (e.g. within the Aadhaar project (Unique Identification Authority of India, 2012) by the Unique Identification Authority of India (UIDAI)). However, security of multi-biometric templates is especially crucial as they contain information regarding multiple traits of the same subject (Nagar et al., 2012). The leakage of any kind of template information to unauthorized individuals constitutes serious security and privacy risks, e.g. permanent tracking of subjects without consent (Ratha et al., 2001) or reconstruction of original biometric traits (e.g. fingerprints (Cappelli et al., 2007) or iris textures (Venugopalan & Savvides, 2011)) might become a realistic threat. Therefore, biometric template protection technologies have been developed in order to protect privacy and integrity of stored biometric data. However, so far, template protection schemes which provide provable security/ privacy, and achieve practical recognition rates have remained elusive, even on small datasets. This bookchapter provides a comprehensive overview of <s> BIB006 </s> A Survey on Multimodal Biometrics and the Protection of Their Templates <s> Combination of Cryptography and Multimodalities <s> As biometric technologies are becoming pervasive, it is imperative to protect the users of these technologies from misuse of their biometric data. However, unlike user credentials in traditional security systems, such as passwords or tokens, biometric features cannot be consistently sampled, and the matching process can be complex. Furthermore, the consequences of losing biometric data can be far more severe than passwords or tokens. Secure sketches, a recently developed cryptographic primitive, allow noisy data to be restored using some helper-data, while providing bounds on how much sensitive information such helper-data would reveal when obtained by malicious parties. In this chapter, we discuss security threats on the use of biometric templates in security systems, and how secure sketches can be used to address these threats under various circumstances. <s> BIB007 </s> A Survey on Multimodal Biometrics and the Protection of Their Templates <s> Combination of Cryptography and Multimodalities <s> This important text/reference presents the latest secure and privacy-compliant techniques in automatic human recognition. Featuring viewpoints from an international selection of experts in the field, the comprehensive coverage spans both theory and practical implementations, taking into consideration all ethical and legal issues. Topics and features: presents a unique focus on novel approaches and new architectures for unimodal and multimodal template protection; examines signal processing techniques in the encrypted domain, security and privacy leakage assessment, and aspects of standardization; describes real-world applications, from face and fingerprint-based user recognition, to biometrics-based electronic documents, and biometric systems employing smart cards; reviews the ethical implications of the ubiquity of biometrics in everyday life, and its impact on human dignity; provides guidance on best practices for the processing of biometric data within a legal framework. <s> BIB008
It is an undeniable fact that the combination of cryptography and multibiometrics introduces a number of successful mechanisms that ensure information privacy. Some of the approaches presented in the previous paragraphs of this section may be adopted as solutions, but, still other situations will occur. Precisely, the alignment of the protected templates is an essential task BIB006 , and the representation of feature vectors remains an important line of research. Experiments on protected biometric data BIB005 lead to the assumption that the low boundaries between the false rejection rates and the error-correction capacities compound a more vulnerable system and at the same time, the requirements for stable biometric features are, definitely, non-trivial. Some of the approaches show that the protocols in the literature do not secure the encoding procedures BIB007 while others provide multiple suggestions for the distribution of reliability, or concentrate the efforts to the improvement of recognition rates BIB008 . With respect to the different multimodal biometrics template protection schemes, the interesting side contains the concentrated trials for a generic framework, focused on unified representation of biometric features, under the combination of the suggested protection designs. Relevant to the mechanisms and for the improvement of security and privacy, the requirements, according to Biometric Template Protection Standardization ISO/IEC 24745 [58] need to be covered and clearly addressed, while the accuracy of each concept should be tested. The last element in this list is some of the most popular introduced privacy methods and the security issues currently on debate. Beyond all the technical cases that arise from the use of multimodalities, when those are applied to template protection schemes, their fusion leads to a number of issues. While, researchers suggest the use of multimodalities, other approaches [57] induce different findings and set the dilemma about the choice of the use of multimodal biometrics instead of uni-modal ones, in order to contribute to a protection of the user against undesired biometric checking. Some other open research questions from privacy aspect, which need to be further examined are: Does the system exclude the threats that can arise, considering the possibility to perform the biometric procedure without notice and/or against the will of the user? How can the user protect himself/herself against undesired biometric checking? One step further, the biometric databases, created to support a range of applications, the possibility of data correlation with health information BIB002 BIB003 BIB001 BIB004 , and the security requirements for data, stored in ePassports or ID cards, cause a risky uncertainty. Also, the very nature of template protection schemes, introduce questions about their efficiency for on-line fast identifications, or situations that involve government applications, and these are some of the areas that need to be covered extensively.