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Towards Practical Privacy-Preserving Protocols

Demmler, Daniel (2019):
Towards Practical Privacy-Preserving Protocols.
Darmstadt, Technische Universität, [Online-Edition: https://tuprints.ulb.tu-darmstadt.de/8605],
[Ph.D. Thesis]

Abstract

Protecting users' privacy in digital systems becomes more complex and challenging over time, as the amount of stored and exchanged data grows steadily and systems become increasingly involved and connected. Two techniques that try to approach this issue are Secure Multi-Party Computation (MPC) and Private Information Retrieval (PIR), which aim to enable practical computation while simultaneously keeping sensitive data private. In this thesis we present results showing how real-world applications can be executed in a privacy-preserving way. This is not only desired by users of such applications, but since 2018 also based on a strong legal foundation with the General Data Protection Regulation (GDPR) in the European Union, that forces companies to protect the privacy of user data by design.

This thesis' contributions are split into three parts and can be summarized as follows:

MPC Tools Generic MPC requires in-depth background knowledge about a complex research field. To approach this, we provide tools that are efficient and usable at the same time, and serve as a foundation for follow-up work as they allow cryptographers, researchers and developers to implement, test and deploy MPC applications. We provide an implementation framework that abstracts from the underlying protocols, optimized building blocks generated from hardware synthesis tools, and allow the direct processing of Hardware Definition Languages (HDLs). Finally, we present an automated compiler for efficient hybrid protocols from ANSI C.

MPC Applications MPC was for a long time deemed too expensive to be used in practice. We show several use cases of real-world applications that can operate in a privacy-preserving, yet practical way when engineered properly and built on top of suitable MPC protocols. Use cases presented in this thesis are from the domain of route computation using BGP on the Internet or at Internet Exchange Points (IXPs). In both cases our protocols protect sensitive business information that is used to determine routing decisions. Another use case focuses on genomics, which is particularly critical as the human genome is connected to everyone during their entire lifespan and cannot be altered. Our system enables federated genomic databases, where several institutions can privately outsource their genome data and where research institutes can query this data in a privacy-preserving manner.

PIR and Applications Privately retrieving data from a database is a crucial requirement for user privacy and metadata protection, and is enabled amongst others by a technique called Private Information Retrieval (PIR). We present improvements and a generalization of a well-known multi-server PIR scheme of Chor et al., and an implementation and evaluation thereof. We also design and implement an efficient anonymous messaging system built on top of PIR. Furthermore we provide a scalable solution for private contact discovery that utilizes ideas from efficient two-server PIR built from Distributed Point Functions (DPFs) in combination with Private Set Intersection (PSI).

Item Type: Ph.D. Thesis
Erschienen: 2019
Creators: Demmler, Daniel
Title: Towards Practical Privacy-Preserving Protocols
Language: English
Abstract:

Protecting users' privacy in digital systems becomes more complex and challenging over time, as the amount of stored and exchanged data grows steadily and systems become increasingly involved and connected. Two techniques that try to approach this issue are Secure Multi-Party Computation (MPC) and Private Information Retrieval (PIR), which aim to enable practical computation while simultaneously keeping sensitive data private. In this thesis we present results showing how real-world applications can be executed in a privacy-preserving way. This is not only desired by users of such applications, but since 2018 also based on a strong legal foundation with the General Data Protection Regulation (GDPR) in the European Union, that forces companies to protect the privacy of user data by design.

This thesis' contributions are split into three parts and can be summarized as follows:

MPC Tools Generic MPC requires in-depth background knowledge about a complex research field. To approach this, we provide tools that are efficient and usable at the same time, and serve as a foundation for follow-up work as they allow cryptographers, researchers and developers to implement, test and deploy MPC applications. We provide an implementation framework that abstracts from the underlying protocols, optimized building blocks generated from hardware synthesis tools, and allow the direct processing of Hardware Definition Languages (HDLs). Finally, we present an automated compiler for efficient hybrid protocols from ANSI C.

MPC Applications MPC was for a long time deemed too expensive to be used in practice. We show several use cases of real-world applications that can operate in a privacy-preserving, yet practical way when engineered properly and built on top of suitable MPC protocols. Use cases presented in this thesis are from the domain of route computation using BGP on the Internet or at Internet Exchange Points (IXPs). In both cases our protocols protect sensitive business information that is used to determine routing decisions. Another use case focuses on genomics, which is particularly critical as the human genome is connected to everyone during their entire lifespan and cannot be altered. Our system enables federated genomic databases, where several institutions can privately outsource their genome data and where research institutes can query this data in a privacy-preserving manner.

PIR and Applications Privately retrieving data from a database is a crucial requirement for user privacy and metadata protection, and is enabled amongst others by a technique called Private Information Retrieval (PIR). We present improvements and a generalization of a well-known multi-server PIR scheme of Chor et al., and an implementation and evaluation thereof. We also design and implement an efficient anonymous messaging system built on top of PIR. Furthermore we provide a scalable solution for private contact discovery that utilizes ideas from efficient two-server PIR built from Distributed Point Functions (DPFs) in combination with Private Set Intersection (PSI).

Place of Publication: Darmstadt
Divisions: 20 Department of Computer Science
20 Department of Computer Science > Cryptography and Privacy Engineering (ENCRYPTO)
DFG-Collaborative Research Centres (incl. Transregio)
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres
Profile Areas
Profile Areas > Cybersecurity (CYSEC)
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 1119: CROSSING – Cryptography-Based Security Solutions: Enabling Trust in New and Next Generation Computing Environments
Date Deposited: 30 Jun 2019 19:55
Official URL: https://tuprints.ulb.tu-darmstadt.de/8605
URN: urn:nbn:de:tuda-tuprints-86051
Referees: Schneider, Prof. Dr. Thomas and Herzberg, Prof. Dr. Amir
Refereed / Verteidigung / mdl. Prüfung: 22 November 2018
Alternative Abstract:
Alternative abstract Language
Es wird zunehmend schwieriger die Privatsphäre von Nutzerdaten in digitalen Systemen zu schützen, da die Menge an gespeicherten und verarbeiteten Daten stetig wächst und Systeme immer komplexer und vernetzter werden. Zwei Techniken, die dieses Problem angehen und darauf abzielen praktische Berechnungen unter gleichzeitigem Schutz der Privatsphäre zu ermöglichen, sind sichere Mehrparteienberechnung (MPC) und Private Information Retrieval (PIR). Diese Dissertation präsentiert Ergebnisse, die zeigen wie Anwendungen aus der Praxis mit Privatsphäre-Schutz versehen werden können. Dies ist nicht nur der Wunsch vieler Anwender, sondern mit der europäischen Datenschutz-Grundverordnung (DSGVO) seit 2018 auch auf einer starken rechtlichen Basis verankert. Die wissenschaftlichen Beiträge dieser Arbeit sind in die folgenden drei Teile gegliedert: MPC Werkzeuge Die Verwendung von MPC-Techniken benötigt fundiertes Hintergrundwissen in einem komplexen Forschungsfeld. Wir stellen dafür Werkzeuge zur Verfügung, die effizient sind und gleichzeitig einen großen Fokus auf Benutzbarkeit legen. Diese Werkzeuge diesen als Basis für viele Folge-Arbeiten und sie erleichtern es Kryptographen, Entwicklern und Forschern MPC Anwendungen zu entwickeln und zu evaluieren. Wir stellen ein Implementierungs-Framework zur Verfügung, das von Protokolldetails abstrahiert, ergänzen dieses mit Bausteinen aus der Hardware-Synthese und erlauben die direkte Verarbeitung von Hardwarebeschreibungs-Sprachen. Weiterhin stellen wir einen Compiler vor, der ANSI-C-Code vollautomatisiert in effiziente, hybride MPC Protokolle übersetzt. MPC Anwendungen MPC war lange Zeit als rein theoretisches Resultat angesehen, das aufgrund seiner Komplexität in der Praxis kaum Verwendung findet. Wir präsentieren mehrere praktische Applikationen, die die Privatsphäre der verarbeiteten Daten schützen und gleichzeitig praktikable Performanz erreichen. Eine Anwendung ist fokussiert auf die Berechnung von Routen mittels des Border Gateway Protokolls (BGP) im Internet sowie deren Verteilung bei Internet Exchange Points (IXPs). In beiden Fällen schützen unsere Protokolle sensitive Unternehmensdaten, die für Routing-Entscheidungen benötigt werden. Ein weiterer Anwendungsfall stammt aus der Genetik und ist insofern von besonderer Relevanz, da das menschliche Genom unveränderlich ist und für die komplette Dauer eines Menschenlebens an ein Individuum gebunden ist. Unser System erlaubt es mehreren medizinischen Institutionen ihre Genomdaten sicher in eine verteilte Genomdatenbank auszulagern und diese zentrale Datenbank unter Schutz der Privatsphäre abzufragen. PIR und Anwendungen Die private Abfrage von Daten aus einer Datenbank als Grundlage für Anonymität und den Schutz von Metadaten wird ermöglicht durch Private Information Retrieval (PIR). Wir zeigen Verbesserungen und die Generalisierung des PIR-Protokolls von Chor et al. sowie eine Implementierung und Evaluation davon. Wir implementieren zudem ein effizientes anonymes Kommunikationssystem auf der Grundlage von PIR. Weiterhin stellen wir eine skalierbare Lösung für private Schnittmengenberechnung (PSI), speziell für den Kontext der privaten Kontaktsynchronisierung vor. Diese basiert auf effizienter 2-Parteien PIR in Kombination mit PSI.German
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