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Privacy Analysis and Protocols for Decentralized Online Social Networks
KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.ORCID iD: 0000-0002-7102-8153
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Decentralized Online Social Networks (DOSNs) are evolving as a promising approach to mitigate design-inherent privacy flaws of logically centralized services such as Facebook, Google+ or Twitter. Common approaches to implement a DOSN build upon a peer-to-peer (P2P) architecture in order to avoid the central aggregation of sensitive user data at one provider-controlled location.

While the absence of a single point of data aggregation strikes the most powerful attacker from the list of adversaries, the decentralization also removes some privacy protection afforded by the provider's intermediation of all communication in a centralized Online Social Network (OSN). As content storage, access right management, retrieval and other administrative tasks of the service become the obligation of the users, it is non-trivial to hide the metadata of objects and information flows, even when the content itself is encrypted. Such metadata is, deliberately or as a side effect, hidden by the provider in a centralized system.

Implementing the different features of a privacy-presvering DOSN does not only face these general challenges but must also cope with the absence of a trusted agent with full access to all data. For example user authentication should provide the same usabilty known from common centralized OSN services, such as ease of changing a password, revoking the access of a stolen device or resetting a forgotten password via e-mail or security questions. All this without relying on a trusted third party such as an identity provider. Another example is user search, where the challenge is to protect user data while making user findable at the same time. An implementation of such a feature in a DOSN has to work without assuming a trusted provider having access to all user profiles maintaining a global search index.

In this work we analyze the general privacy-problems in a DOSN, especially those arising from metadata. Furthermore, we suggest two privacy-preserving implementations of standard OSN features, i.e., user authentication via password-login and user search via a knowledge threshold. Both implementations do not rely on a trusted, central provider and are therefore applicable in a DOSN cenario but can be applied in other P2P or low-trust environments as well.

Abstract [sv]

I dagens populära sociala nätverkstjänster, såsom Facebook, Google+ och Twitter, finns en risk för integritetskränkningar. Risken är en oundviklig konsekvens av den logiskt centraliserade struktur som dessa tjänster bygger på.  Decentraliserade sociala nätverkstjänster (eng. Decentralized Online Social Networks, DOSNs) är en lovande utveckling för att minska risken och skydda användarnas personliga information från tjänsteleverantören och dem som leverantören samarbetar med. Ett vanligt sätt att implementera ett DOSN är genom en icke-hierarkisk nätverksarkitektur (eng. peer-to-peer network) för att undvika att känsliga personuppgifter ansamlas på ett ställe under tjäns televerantörens kontroll.  

Att inte längre ha en tjänsteleverantör som har tillgång till alla data tar bort den största risken för integritetskränkningar. Men genom att ersätta den centrala tjänsteleverantören med ett decentraliserat system tar vi även bort visst integritetsskydd. Integritetsskyddet var en konsekvens av att förmedlingen av all användarkommunikation skedde genom tjänsteleverantörens mellanservrar. När ansvaret för lagring av innehållet, hantering av behörigheterna, åtkomst och andra administrativa uppgifter övergår till användarna själva, då blir det en utmaning att skydda metadata för objekten och informationsflöden, även om innehållet är krypterat. I ett centraliserat system är dessa metadata faktiskt skyddade av tjänsteleverantören - avsiktligt eller som en sidoeffekt.  

För att implementera de olika funktioner som ska finnas i ett integritetsskyddande DOSN, är det nödvändigt att både lösa dessa generella utmaningar och att hantera frånvaron av ett betrodd tredjepart som har full tillgång till all data. Autentiseringen av användarna, till exempel, borde ha samma användbarhet som finns i centraliserade system. Det vill säga att det är lätt att ändra lösenordet, dra tillbaka rättigheterna för en stulen klientenhet, eller återställa ett glömt lösenord med hjälp av e-post eller säkerhetsfrågor - allt utan att förlita sig på en betrodd tredjepart. Ett annat exempel är funktionen att kunna söka efter andra användare. Utmaningen där är att skydda informationen om användarna samtidigt som det måste vara möjligt att hitta användare baserad på samma information. En implementation av denna funktion i ett DOSN måste klara sig utan en betrodd tjänsteleverantör som med tillgång till alla användares data kan upprätthålla ett globalt sökindex.

I den här avhandlingen analyserar vi de generella risker för integritetskränkningar i DOSN, särskilt de som orsakas av metadata. Dessutom föreslår vi två integritetskyddande implementationer av vanliga funktioner i en socialt nätverkstjänst: lösenordbaserad användarautentisering och en användarsökfunktionen med en kunskaptröskel. Båda implementationerna är lämpliga för DOSN-scenarier eftersom de klarar sig helt utan en betrodd, central tjänstleverantör, och kan därför också användas i andra sammanhang: såsom icke-hierarkiska nätverk eller andra system som måste klara sig utan en betrodd tredjepart.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , viii, 81 p.
Series
TRITA-CSC-A, ISSN 1653-5723 ; 2015:06
Keyword [en]
privacy, online social networks, decentralization
National Category
Computer Science
Research subject
Computer Science
Identifiers
URN: urn:nbn:se:kth:diva-165377ISBN: 978-91-7595-546-9 (print)OAI: oai:DiVA.org:kth-165377DiVA: diva2:808202
Presentation
2015-05-29, E2, Lindstedtsvägen 3 (03 tr), KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , SSF FFL09-0086Swedish Research Council, VR 2009-3793
Note

QC 20150428

Available from: 2015-04-28 Created: 2015-04-27 Last updated: 2015-04-28Bibliographically approved
List of papers
1. The devil is in the metadata - New privacy challenges in decentralised online social networks
Open this publication in new window or tab >>The devil is in the metadata - New privacy challenges in decentralised online social networks
2012 (English)In: 2012 IEEE International Conference on Pervasive Computing and Communications Workshops, PERCOM Workshops 2012, IEEE , 2012, 333-339 p.Conference paper, Published paper (Refereed)
Abstract [en]

Decentralised Online Social Networks (DOSN) are evolving as a promising approach to mitigate design-inherent privacy flaws of logically centralised services such as Facebook, Google+ or Twitter. A common approach to build a DOSN is to use a peer-to-peer architecture. While the absence of a single point of data aggregation strikes the most powerful attacker from the list of adversaries, the decentralisation also removes some privacy protection afforded by the central party's intermediation of all communication. As content storage, access right management, retrieval and other administrative tasks of the service become the obligation of the users, it is non-trivial to hide the metadata of objects and information flows, even when the content itself is encrypted. Such metadata is, deliberately or as a side effect, hidden by the provider in a centralised system. In this work, we aim to identify the dangers arising or made more severe from decentralisation, and show how inferences from metadata might invade users' privacy. Furthermore, we discuss general techniques to mitigate or solve the identified issues.

Place, publisher, year, edition, pages
IEEE, 2012
Keyword
privacy, social networks, metadata, decentralized social networks
National Category
Computer Systems
Research subject
SRA - ICT
Identifiers
urn:nbn:se:kth:diva-88041 (URN)10.1109/PerComW.2012.6197506 (DOI)2-s2.0-84861539737 (Scopus ID)978-146730907-3 (ISBN)
Conference
2012 IEEE International Conference on Pervasive Computing and Communications Workshops, PERCOM Workshops 2012; Lugano; 19 March 2012 through 23 March 2012
Funder
Swedish Research CouncilICT - The Next Generation
Note

QC 20120806

Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2016-11-15Bibliographically approved
2. Passwords in Peer-to-Peer
Open this publication in new window or tab >>Passwords in Peer-to-Peer
Show others...
2012 (English)In: Peer-to-Peer Computing (P2P), 2012 IEEE 12th International Conference on, IEEE , 2012, 167-178 p.Conference paper, Published paper (Refereed)
Abstract [en]

One of the differences between typical peer-to-peer (P2P) and client-server systems is the existence of user accounts. While many P2P applications, like public file sharing, are anonymous, more complex services such as decentralized online social networks require user authentication. In these, the common approach to P2P authentication builds on the possession of cryptographic keys. A drawback with that approach is usability when users access the system from multiple devices, an increasingly common scenario. In this work, we present a scheme to support logins based on users knowing a username-password pair. We use passwords, as they are the most common authentication mechanism in services on the Internet today, ensuring strong user familiarity. In addition to password logins, we also present supporting protocols to provide functionality related to password logins, such as resetting a forgotten password via e-mail or security questions. Together, these allow P2P systems to emulate centralized password logins. The results of our performance evaluation indicate that incurred delays are well within acceptable bounds.

Place, publisher, year, edition, pages
IEEE, 2012
Series
IEEE International Conference on Peer-to-Peer Computing, ISSN 2161-3567
Keyword
Authentication mechanisms, Client-server systems, Complex services, Cryptographic key, File Sharing, Multiple devices, Online social networks, P2P applications, P2P system, Peer to peer, Performance evaluation, User authentication, Users access
National Category
Computer Science Telecommunications
Identifiers
urn:nbn:se:kth:diva-107785 (URN)10.1109/P2P.2012.6335797 (DOI)000312674500024 ()2-s2.0-84870369349 (Scopus ID)978-146732862-3 (ISBN)
Conference
IEEE 12th International Conference on Peer-to-Peer Computing, P2P 2012; Tarragona;3 September 2012 through 5 September 2012
Funder
Swedish Foundation for Strategic Research , SSF FFL09-0086Swedish Research Council, VR 2009-3793ICT - The Next Generation
Note

QC 20130111

Available from: 2012-12-17 Created: 2012-12-17 Last updated: 2017-05-05Bibliographically approved
3. User Search with Knowledge Thresholds in Decentralized Online Social Networks
Open this publication in new window or tab >>User Search with Knowledge Thresholds in Decentralized Online Social Networks
2014 (English)In: PRIVACY AND IDENTITY MANAGEMENT FOR EMERGING SERVICES AND TECHNOLOGIES, 2014, 188-202 p.Conference paper, Published paper (Refereed)
Abstract [en]

User search is one fundamental functionality of an Online Social Network (OSN). When building privacy-preserving Decentralized Online Social Networks (DOSNs), the challenge of protecting user data and making users findable at the same time has to be met. We propose a user-defined knowledge threshold ("find me if you know enough about me") to balance the two requirements. We present and discuss protocols for this purpose that do not make use of any centralized component. An evaluation using real world data suggests that there is a promising compromise with good user performance and high adversary costs.

Series
IFIP Advances in Information and Communication Technology, ISSN 1868-4238 ; 421
Keyword
Decentralized Online Social Networks, Privacy, User Search
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-155157 (URN)000342688200015 ()978-3-642-55137-6; 978-3-642-55136-9 (ISBN)
Conference
8th IFIP WG 9.2, 9.5, 9.6/11.7, 11.4, 11.6 International Summer School, JUN 17-21, 2013, Nijmegen, NETHERLANDS
Note

QC 20141103

Available from: 2014-11-03 Created: 2014-10-31 Last updated: 2016-11-15Bibliographically approved

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Greschbach, Benjamin

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