Anonymous Digital Identity in e-Government DISSERTATION DER WIRTSCHAFTSWISSENSCHAFTLICHEN FAKULTAT¨ DER UNIVERSITAT¨ ZURICH¨ zur Erlangung der W¨urde eines Doktors der Informatik vorgelegt von NIKLAS AUERBACH aus Deutschland genehmigt auf Antrag von Prof. Dr. Lutz Richter Prof. Dr. Gerhard Schwabe Juni 2004 Die Wirtschaftswissenschaftliche Fakult¨atder Universit¨atZ¨urich, Lehrbe- reich Informatik, gestattet hierdurch die Drucklegung der vorliegenden Dis- sertation, ohne damit zu den darin ausgesprochenen Anschauungen Stellung zu nehmen. Z¨urich, den 23. Juni 2004* Der Lehrbereichsvorsteher: Prof. Dr. Martin Glinz *Datum der Promotionsfeier Abstract The ongoing implementation of e-government has brought many governments to consider issuing digital identity cards. This thesis focuses on the impact of digital identity cards on the citizen’s privacy. Potential privacy threats are discussed and countermeasures that pertain to enhancing privacy are proposed. We advocate that digital identity should not solely be based on elements that disclose a citizens identity. Instead this thesis proposes a concept for digital identity cards that includes an anonymous component. This proposed approach is different from the approach taken by the current projects for digital identity cards. We propose a concept that comprises pseudonymous credentials as part of the citizen’s digital identity. We discuss current implementations of pseudonymous credential systems and consider problems resulting from the implementation in resource-restricted smart card environments. We discuss requirements for the use of credentials as part of the citizen’s digital identity. We discuss conceptual issues that must be ad- dressed for a deployment of credentials. We consider the infrastructure that is necessary to support pseudonymous credentials. We discuss conceptual issues such as the choice of credential system, devices for the secure storage of credentials, non-transferability and revocation of digital credentials. An architecture is proposed that supports the use of the extended form of digital identity. We discuss barriers that must be overcome on the way to imple- mentation. With the ongoing migration towards digital identity cards, we expect that privacy will become an issue of growing importance. This the- sis contributes to the discussion on privacy in the domain of e-government and proposes anonymous services based on pseudonymous credentials as a means to alleviate potential privacy problems related to the use of electronic identity cards. Zusammenfassung Im Zuge nationaler e-Government Initiativen haben einige europ¨aische Re- gierungen bereits elektronische Identit¨atskarten ausgegeben. Diese Disserta- tion befasst sich mit den Auswirkungen von digitalen Identit¨atskarten auf die Privatsph¨aredes B¨urgers. Potentielle Bedrohungen f¨urdie Privatheit werden aufgezeigt und Gegenmassnahmen, die zum Schutz der Privatheit beitragen, werden vorgeschlagen. Diese Arbeit schl¨agt vor, dass die digi- tale Identit¨atdes B¨urgers nicht nur aus Elementen bestehen soll, welche die Identit¨at des B¨urgers preisgeben. Stattdessen stellt diese Arbeit ein Konzept f¨urelektronische Identit¨atskarten vor, das eine anonyme Komponente um- fasst. Der vorgeschlagene Ansatz unterscheidet sich von den Ans¨atzen, die von gegenw¨artigen Projekten f¨urelektronische Identit¨atskarten implemen- tiert werden. Das vorgeschlagene Konzept umfasst pseudonyme Creden- tials als Teil der digitalen Identit¨at des B¨urgers. Verf¨ugbare Ans¨atzef¨ur pseudonyme Credential Systeme werden besprochen und Probleme disku- tiert, die sich aus einer Implementation in Ressourcen-beschr¨ankten Umge- bungen wie Smart Cards ergeben. Wir besprechen Anforderungen f¨urden Einsatz von Credentials in e-Government. Infrastrukturkomponenten, die f¨ur einen Einsatz von Credentials notwendig sind, werden diskutiert. Konzep- tionelle Fragen werden besprochen, wie die Wahl eines geeigneten Creden- tial Systems, die sichere Aufbewahrung von Credentials, Methoden f¨urdie Gew¨ahrleistung der nicht-Ubertragbarkeit¨ sowie Algorithmen f¨urdie Re- vokation von pseudonymen Credentials. Eine Architektur zur Umsetzung der erweiterten digitalen Identit¨atwird vorgeschlagen. Hindernisse wer- den diskutiert, die auf dem Weg zur Implementation ¨uberwunden werden m¨ussen. Durch die fortw¨ahrende Migration in Richtung elektronischer Iden- tit¨atskarten erwarten wir, dass das Thema Privatheit wachsende Bedeutung erlangen wird. Diese Arbeit leistet einen wissenschaftlichen Beitrag zur Diskussion um das Thema der Privatheit im Bereich von e-Government und schl¨agt einen anonymen Dienstzugang als eine Massnahme vor, die m¨ogliche negative Auswirkungen von elektronischen Identit¨atskarten auf die Privatheit verringern kann. Acknowledgements This thesis was written during my time as a research assistant at the Depart- ment of Informatics (IFI) at the University of Zurich. First and foremost, I would like to express my sincere gratitude to my thesis advisor Prof. Dr. Lutz Richter for giving me the chance to work as part of his research team, for supervising my thesis and for always having confidence in my work. I would like to thank Prof. Dr. Gerhard Schwabe for receiving me into his research team, for his support and feedback during the writing of this thesis and for acting as a co-supervisor. I would also like to thank Dr. Reinhard Riedl for bringing me into the e-Mayor project, for supporting my research and for acting as a co-supervisor. I would like to express my gratitude to Dr. Jan Camenisch at the IBM Zurich Research Laboratory in R¨uschlikon for numerous discussions on pseu- donymous credential systems and for the willingness to establish a joint study agreement. I would especially like to thank Dr. Camenisch for providing me with a prototype of the Idemix pseudonymous credential system for use in my research. Furthermore, I would like to thank the following people who have all contributed to this work: • Nico Maibaum at the University of Rostock for a fruitful cooperation during and after the FASME project and for providing feedback on my research. • Prof. Dr. Clemens H. Cap for numerous discussions on the topic of credentials and for inviting me to present my work to his research group in Rostock. I would also like to thank the members of Prof. Dr. Cap’s research group as they have taken time for many productive discussions. • Andr´as Kiraly for implementing a prototypical system for the use of credentials in Web-based service delivery as part of a diploma thesis. Andr´as Kiraly also developed a Big Integer library for the Java Card that was used for parts of my research. • Dr. Els Van Herreweghen and Roger D. Zimmermann at IBM’s Zurich Research Laboratory in R¨uschlikon for fruitful discussions. • All partners that were involved in the FASME project for interesting discussions at project meetings and workshops. • My parents Doris and Hans-Joachim Auerbach for the proof-reading the manuscript, for motivating me throughout the writing of this thesis and for always believing in me. • My partner Petra Baumg¨artner for her patience and her support during the writing of this thesis. Part of the work underlying this thesis has been performed as part of the FASME project (Facilitating Administrative Services for Mobile Europeans). The project has been funded by the European Commission in the Information Society Technology program under contract number IST-1999-10882. Table of Contents List of Figures viii List of Tables ix 1 Introduction 1 1.1 Research Contributions . 3 1.2 Structure of the Thesis . 4 2 Digital Identity and Anonymity 7 2.1 Identity, Anonymity and Pseudonymity . 7 2.1.1 Human Identity . 7 2.1.2 Human Identification . 8 2.1.3 Anonymity . 9 2.1.4 Anonymity in Computer Supported Cooperative Work 10 2.1.5 Pseudonymity . 12 2.1.6 Revocable Anonymity . 12 2.2 Digital Identity . 14 2.2.1 Digital Identity in Electronic Service Access . 17 2.2.2 Authentication of Digital Identities . 19 2.3 Summary . 21 3 Introduction to e-Government 23 3.1 e-Government . 23 3.1.1 Definition of e-Government . 24 3.1.2 Differentiation Between e-Government and e-Business . 26 3.1.3 e-Government Services . 28 3.2 One-Stop e-Government and Service Portals . 30 3.3 Uptake of Electronic Service Delivery in Europe . 32 3.4 Challenges of International e-Government Services . 36 3.5 Summary . 37 i ii Table of Contents 4 Technical State of the Art 39 4.1 Digital Credentials . 39 4.1.1 Characteristics of Digital Credentials . 41 4.2 Anonymous and Pseudonymous Credential Systems . 42 4.2.1 Implementations of Credential Systems . 43 4.3 Public-Key Certificates and Public-Key Infrastructure . 48 4.3.1 Public-Key Infrastructure . 49 4.3.2 X.509 Public-Key and Attribute Certificates . 50 4.4 Group Signature Schemes . 52 4.5 Identity Management . 54 4.6 Anonymous Communications in the Internet . 54 4.7 Electronic Identity and Citizen Card Initiatives in Europe . 55 4.7.1 General Approach Taken to Electronic Identity Cards . 56 4.7.2 Electronic Identity Card Projects in Europe . 58 4.8 Summary . 62 5 From Privacy to Anonymous Transactions in e-Government 65 5.1 Privacy in e-Government . 65 5.1.1 The Concept of Privacy . 66 5.1.2 Informational Privacy in e-Government . 67 5.1.3 The Sensitive Nature of Information in e-Government . 68 5.1.4 IT Security Goals and Informational Privacy . 69 5.2 Data Protection Legislation . 70 5.2.1 A Brief History of Data Protection Legislation . 70 5.2.2 Basic Data Protection Principles . 71 5.2.3 EU Data Protection Directive . 73 5.2.4 Local Implementations of the Data Protection Directive 74 5.3 Potential Threats to Privacy Posed by e-Government Systems 75 5.3.1 General Threats To Privacy . 75 5.3.2 Threats To Privacy Posed by the Introduction of Citi- zen Cards . 78 5.4 Measures to Enhance Privacy . 81 5.4.1 General Measures to Enhance Privacy . 81 5.4.2 Privacy-enhancing Measures for Smart Cards . 86 5.4.3 A Conceptual Model of Privacy-Enhancing Measures .