A multi-modal biometric fusion implementation for ABC Systems

Daniel Cuesta Cantarero, David Antonio Pérez Herrero, Fernando Martín Méndez Security Systems Indra Sistemas

Alcobendas, Spain

Abstract— In this paper, we introduce a multi-modal approach for traveller biometric identity verification, in the context of the Spanish Automated Border Control (ABC) implementation. An ABC is an automated system which reads and authenticates the electronic travel document, verifies the identity of the document holder, performs background checks and resolves the eligibility for border crossing. This paper focuses on the second stage of the automated process, the identity verification, based on the biometric data available in the electronic travel document. According to the nature of the travel document, a standardized facial image (1st and 2nd generation electronic Passport, Spanish electronic ID card), two standardized fingerprint images (2nd generation electronic Passport) or fingerprint Match-on-Card features (Spanish electronic ID card) are available. While the facial image can be considered the de facto standard biometric modality for ABC systems, fingerprint availability allows for security enhancement and false rejection rates improvement.

Keywords— Automated Border Control; electronic passport; multi-biometric; multi-modal; biometric fusion.

I. INTRODUCTION According to Boeing [1], despite the global economical

uncertainty, passenger traffic worldwide in 2011 rose 6 percent above 2010 levels. The expected trend is a steady 5 percent annual growth over the next 20 years. This situation implies important side effects at the international Border Crossing Points (BCPs), which cannot be simply addressed due to the limited Border Authorities infrastructures and human resources. Additionally, optimal allocation of such human resources requires them to focus on high-risk individuals, and not in routine-checks. ABC systems strategically deployed at international airports have proven during the latest years to be cost effective solutions to the increasingly growth of travellers, facilitating the border crossing while maintaining the required security levels at the BCPs, allowing bona fide, low risk travellers to cross the border in a quick and efficient way.

According to the European Agency for the Management of Operational Cooperation at the External Borders of the Member States of the European Union (Frontex) [3], the principal components of an Automated Border Control (ABC) are the physical barriers (one or two e-Gates), a full page electronic Passport scanner for text recognition and chip reading, a monitor displaying instructions to the traveller, the

biometric capture device(s) and the system management hardware and software.

ABC systems in Europe can be classified into two different groups, depending on the source of the biometric sample which uniquely and undoubtedly identifies the traveller: Registered Traveller Programmes (RTP), aimed at frequent pre-vetted, pre-screened travellers who are required to enrol their biometric marker in the system and regular ABCs, aimed at EU citizens, using a biometrically enabled electronic travel document, usually an ICAO compliant e-Passport. This paper focuses on the latter. ABC system references of both modalities are presented in TABLE I.

In terms of topology, Frontex classify existing ABC systems into three categories:

• One-Step Process, when the document verification, the identity verification and the border crossing happens in one single process.

• Integrated Two-Step Process, when the document verification and eligibility to use the system is performed in advance and, if successful, the identity verification process is performed in a different stage within the same physical location.

• Segregated Two-Step Process, when the process of traveller verification and the border crossing are completely separated. A token is needed to link both processes, usually in the form of a biometric sample.

European Member States are responsible of issuing biometrically enabled Passports to their citizens since August 2006, as per EU Council’s December 2004 regulation n° 2252/2004 [2]. The first generation e-Passport, which features one biometric modality only, i.e. the facial marker, is now broadly available. The second generation e-Passport featuring two biometric modalities, i.e. the facial and fingerprint markers, has been in circulation since June 2009. It is envisaged that 90% of the passports available worldwide will be electronic by 2016.

Some ABC systems deployed by certain Member States, such as Spain, are designed to allow their own nationals to perform the automated border crossing by using their national ID card. These ID cards feature either the same ICAO compliancy as the e-Passports or proprietary mechanisms with similar functionality, thus allowing equivalent security levels

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for the document authentication and biometric identity verification processes. The Spanish e-ID card, for example, incorporates advanced chip authentication mechanisms, a facial image and fingerprint Match-On-Card capabilities.

TABLE I. ABC SYSTEMS IN EUROPE

Country Name Eligibility requirements

Biometric marker

Registered Traveller Programmes (pre-enrollment required)

Germany ABG 18 or above. Schengen citizens Passport holders

Iris

United Kingdom

IRIS 18 or above. Schengen citizens Passport holders

Iris mySense

France PARAFES

18 or above. Schengen citizens Passport holders Nationals of the third States, living of the EU holders of a membership card of family of a National of the EU.

Fingerprint

Netherlands Privium

Schegen citizens and diplomats stationed in the Netherlands. Passport holders.

Iris

ABC Systems (no pre-enrollment)

Portugal RAPID 18 or above. Schengen citizens e-Passport holders

Face

United Kingdom ABC System

18 or above. Schengen citizens e-Passport holders

Face

Finland ABC 18 or above. Schengen citizens e-Passport holders

Face

Germany EasyPass 18 or above. Schengen citizens e-Passport holders

Face

Spain ABC System

18 or above. Schengen citizens e-Passport holders or Spanish e-ID holders

Face & Fingerprint

Netherlands No-Q 18 or above. Schengen citizens e- Passport holders

Face

II. THE SPANISH ABC SYSTEM Inaugurated in late May 2010, the Spanish ABC System

features two different topologies in selected terminals at Barajas and El Prat international airports: One-Step Process and Segregated Two-Step Process.

The One-Step Process ABC takes the form of a mantrap, while the Segregated Two-Step Process ABC combines six kiosks, where the traveller’s identity verification takes place, with two gates.

The facial image is the main biometric modality, while the traveller’s fingerprint is used in three different scenarios:

• In the Segregated Two-Step Process it serves as the token to grant the exit.

• During the identity verification process of the Spanish nationals, the live captured fingerprint image is used in a Match-on-Card operation when the travel document is the Spanish e-ID card.

• During the identity verification process of the Spanish nationals, the live captured fingerprint image is compared against the reference data stored in the chip when the travel document is the Spanish second generation e-Passport. This could also apply to other EU citizens, as soon as the certificates required to extract the fingerprint reference images are available.

The decision matrix in the original setup of the Spanish ABC system required that the result of both biometric modalities comparisons were satisfactory in order to allow the exit to the traveller. If either the facial verification or the fingerprint verification (when required) fails, the system considered the traveller identity verification process unsuccessful.

The decision matrix required that the fingerprint image was captured for all the Spanish citizens (using their Spanish e-ID cards or second generation e-Passports), in a systematic way.

A statistic of a three month period during summer 2012 is shown in the TABLE II.

TABLE II. 4 MONTH STATISTICS OF THE ORIGINAL DECISION MATRIX

Country Total ABC

usage Global

Biometric FRR Facial FRR Fingerprint

FRR AUT 215 5.12% 5.12% 0.00%BEL 531 21.59% 21.59% 0.00%BGR 135 3.73% 3.73% 0.00%CHE 217 5.09% 5.09% 0.00%CYP 5 0.00% 0.00% 0.00%CZE 97 10.53% 10.53% 0.00%D 1,540 10.18% 10.18% 0.00%DNK 152 13.16% 13.16% 0.00%ESP 67,508 16.40% 13.34% 3.29%EST 15 7.14% 7.14% 0.00%FIN 155 4.52% 4.52% 0.00%FRA 2,687 12.69% 12.69% 0.00%GBR 10,914 7.54% 7.54% 0.00%GRC 187 2.67% 2.67% 0.00%HUN 70 8.57% 8.57% 0.00%IRL 749 8.58% 8.58% 0.00%ISL 10 0.00% 0.00% 0.00%ITA 2,757 15.79% 15.79% 0.00%LIE 1 0.00% 0.00% 0.00%LTU 56 8.93% 8.93% 0.00%LUX 13 0.00% 0.00% 0.00%LVA 56 1.79% 1.79% 0.00%MLT 10 10.00% 10.00% 0.00%NLD 990 13.54% 13.54% 0.00%NOR 97 16.49% 16.49% 0.00%POL 214 10.33% 10.33% 0.00%PRT 2,172 5.45% 5.45% 0.00%ROU 367 7.42% 7.42% 0.00%SVK 49 14.29% 14.29% 0.00%SVN 40 10.00% 10.00% 0.00%SWE 397 7.61% 7.61% 0.00%TOTAL 92,406 14.55% 12.32% N/A

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The TABLE II. summarizes the travellers usage of the ABC System in a four month period of time and their related biometric results, grouped by country.

The Country column identifies the traveller’s country of origin, as described in the ICAO 9303 standard [6] (Part 1, Volume 1, Section IV, Appendix 7, Part A).

The Total ABC usage column counts the total number of system uses per country of origin.

The Global biometric FRR denotes the unsuccessful border crossings rate due to facial and/or fingerprint verification. Only the Spanish travellers

The Facial FRR denotes the unsuccessful border crossings rate due to facial verification only.

The Fingerprint FRR denotes the unsuccessful border crossings rate due to fingerprint verification only. This column has only meaning for the Spanish citizens because, although the current implementation of the ABC System is ready to process the 2nd generation passports from any country, only the cryptographic keys from Spain are available to read the fingerprint.

III. REASONS THAT MOTIVATED A MULTI-MODAL FUSION

The statistics shown that, even when the 96.61% of the Spanish citizens using a fingerprint-enabled travel document could cross the border after a successful fingerprint biometric comparison, up to 13.34% of them would be rejected because of the facial verification result. An efficient multi-modal biometric fusion algorithm would improve the error rates and the overall security level of the system.

The improvement of the system error rates would reflect in a better experience to the user, who will not be wrongly rejected to cross the border, and an increment in the traveller flow efficiency.

The fingerprint verification step was performed in a systematic way, but not universally: only the Spanish travellers bearing an e-ID or a second generation e-Passport would suffer the additional annoyance of the fingerprint capture in the One-Step Process ABC. With the implementation of a multi-modal biometric fusion approach, the holders of fingerprint-enabled travel documents would instead benefit from the extra biometric information, and only when necessary.

IV. MULTI-MODAL FUSION IN THE SPANISH ABC The multi-modal implementation is based on ISO/IEC TR

24722 [4], following the model of a cascaded decision-level fusion.

Two thresholds were selected for the facial verification subsystem: the lower threshold would allow the system to undoubtedly reject the border crossing to travellers not reaching the minimum score; the upper threshold would allow the system to undoubtedly allow the border crossing to travellers exceeding the score. Only those travellers with a

comparison score falling in the uncertainty zone between the lower and the upper thresholds would be required to present their fingerprint for additional verification.

Two different scenarios shall be considered. When the traveller uses an Spanish e-ID card, a Match-on-Card operation is performed inside the card chip. Thus, there is no fingerprint comparison score, but a logical (true, false) result.

Fig. 1. Multi-biometric implementation for the Spanish e-ID card

FACIAL VERIFICATION

result < lowerthreshold?

Negative biometriccomparison Yes

No

FINGERPRINT VERIFICATION(Match On Card)

result > upperthreshold

Positive biometriccomparisonYes

No

Success?

No

Yes

The second scenario, for second generation e-Passport holders, makes use of the fusion algorithm of the biometric technology manufacturer. This fusion algorithm is also based on ISO/IEC TR 24722, following the model of a score-level fusion.

Fig. 2. Multi-biometric implementation for the 2nd generation e-Passport

FACIAL VERIFICATION

result < lowerthreshold?

Negative biometriccomparison Yes

No

BIOMETRIC FUSION(NEUROTECHNOLOGY

result > upperthreshold

Positive biometriccomparisonYes

No

Success?

No

Yes

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TABLE III. FEBRUARY 2013 STATISTICS

Country Total ABC

usage Global

Biometric FRR Facial FRR Fingerprint

FRR AUT 25 8.00% 8.00% 0.00%BEL 108 10.10% 10.10% 0.00%BGR 26 4.00% 4.00% 0.00%CHE 55 12.96% 12.96% 0.00%CYP 1 0.00% 0.00% 0.00%CZE 19 0.00% 0.00% 0.00%D 240 10.88% 10.88% 0.00%DNK 22 18.18% 18.18% 0.00%ESP 13,478 3.72% 12.23% 4.77%EST 11 9.09% 9.09% 0.00%FIN 28 3.57% 3.57% 0.00%FRA 647 8.85% 8.85% 0.00%GBR 2,520 5.19% 5.19% 0.00%GRC 37 8.11% 8.11% 0.00%HUN 28 11.54% 11.54% 0.00%IRL 173 9.64% 9.64% 0.00%ISL 3 0.00% 0.00% 0.00%ITA 577 15.29% 15.29% 0.00%LTU 14 7.14% 7.14% 0.00%LUX 4 0.00% 0.00% 0.00%LVA 16 6.25% 6.25% 0.00%MLT 1 0.00% 0.00% 0.00%NLD 177 11.86% 11.86% 0.00%NOR 25 16.00% 16.00% 0.00%POL 30 10.00% 10.00% 0.00%PRT 443 1.36% 1.36% 0.00%ROU 94 10.99% 10.99% 0.00%SVK 11 0.00% 0.00% 0.00%SVN 7 14.29% 14.29% 0.00%SWE 64 1.59% 1.59% 0.00%TOTAL 18,884 4.78% 9.30% N/A

The results of the multi-modal implementation during February 2013 are shown in TABLE III.

The meaning of the Country, Total ABC usage, Facial FRR and Fingerprint FRR columns is the same as described in section II, THE SPANISH ABC SYSTEM.

The Global Biometric FRR column represents the multi-modal biometric fusion result, which has only impact in the Spanish travellers border crossings, where the fingerprint verification process can also be performed.

In the original Spanish ABC System setup, only 85.45% of the travellers were able to use the system. After the multi-modal biometric verification was implemented, the biometric overall error rates lowered to 4.78%, allowing 95.22% of the travellers to use the system.

Although the required cryptographic keys to extend the multi-modal fusion to other EU travellers were not available during the statistics calculation, the majority of the travellers are Spanish, so the overall FRR is significantly improved.

REFERENCES

[1] Boeing “Current Market Outlook 2012-2031” http://www.boeing.com/boeing/commercial/cmo/

[2] “COUNCIL REGULATION (EC) No 2252/2004 of 13 December 2004 on standards for security features and biometrics in passports and travel documents issued by Member State”, EC Council, December 2004. http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2004:385:0001:0006:EN:PDF .

[3] “Best Practice Technical Guidelines for Automated Border Control (ABC) Systems”, Frontex – Research and Development Unit, v2.0, August 2012. http://www.frontex.europa.eu/assets/Publications/Research/Best_Practice_Technical_Guidelines_for_Automated_Border_Control_Systems.pdf

[4] ISO/IEC 24722:2007 Information technology -- Biometrics-- Multimodal and other multibiometric fusion

[5] Guidelines on electronic – Machine Readable Travel Documents & Passenger Facilitation. Version – 1.0. April 17, 2008. http://legacy.icao.int/icao/en/atb/meetings/2008/TAGMRTD18/TagMrtd18_wp03.pdf

[6] ICAO 9303 – Machine Readable Travel Documents, Sixth Edition – 2006. http://www.icao.int/publications/pages/publication.aspx?docnum=9303

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