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Privacy-enhanced Microblogging

Senftleben, Marius (2018):
Privacy-enhanced Microblogging.
Darmstadt, Technische Universität, [Online-Edition: http://tuprints.ulb.tu-darmstadt.de/7554],
[Ph.D. Thesis]

Abstract

Microblogging is a popular form of Online Social Networking (OSN) activity. It allows users to send out short and succinct messages in a one-to-many publish-subscribe manner. Most current service providers are centralized and deploy a client-server model with unencrypted message content. As a consequence, all user behavior can, by default, be monitored, and censoring based on message content can easily be enforced on the server side. Also, the centralized services can be seen as a single point of failure and can become severely disrupted either by disconnecting the service from the Internet or by Internet outages. These privacy issues and the susceptibility of the services to censorship are not only theoretical, but a variety of incidents have shown that these issues are readily exploited. As a consequence, it would be desirable if alternative microblogging solutions were available that offer additional privacy features and which are more resilient to censorship. In this thesis, a distributed, peer-to-peer based microblogging system consisting of mobile smartphone-equipped users that exchange messages, encrypted under a group key, in an anonymous and censorship-resistant manner is proposed, which alleviates the privacy and censorship issues of most current centralized microblogging architectures. Users conduct peer synchronizations to exchange messages, i.e., the bidirectional exchange of a prepared message buffer whenever two users are in proximity of each other and able to establish a direct link using local communication means such as Bluetooth. The way in which the send buffer is filled with messages is determined by the use of a given synchronization strategy. To show the feasibility of the proposed microblogging system, we experimentally evaluate the message spread with simulations that run on a wide range of synthetic and real-world mobility inputs. We show that such systems are working for a range of mobility and network settings, and we evaluate the effects of using different synchronization strategies. In addition to a normal operation of the network, we also test it under adversarial conditions, e.g., under the presence of users which jam the network or send spam. Since the message propagation in the purely peer-to-peer based system is dependent on the mobility the users exhibit as well as the number of users encountered, which are needed to conduct peer synchronizations, the message spread can be slow to non-existent, if parts of the network are segmented and users can not exchange messages via peer synchronizations. In such cases, the devised solution for a higher message spread is facilitated by employing a server that stores the messages of multiple groups in an Oblivious RAM (ORAM) data structure which can be accessed by users at their own discretion. On demand, users read or write their group-encrypted messages obliviously, without the server getting to know anything about the accesses that took place by the users including the message accessed or whether the access was a read or write access. In total, the microblogging solution's use is feasible, but the design decisions required for anonymity result in a delayed spread of messages on a best effort basis.

Item Type: Ph.D. Thesis
Erschienen: 2018
Creators: Senftleben, Marius
Title: Privacy-enhanced Microblogging
Language: English
Abstract:

Microblogging is a popular form of Online Social Networking (OSN) activity. It allows users to send out short and succinct messages in a one-to-many publish-subscribe manner. Most current service providers are centralized and deploy a client-server model with unencrypted message content. As a consequence, all user behavior can, by default, be monitored, and censoring based on message content can easily be enforced on the server side. Also, the centralized services can be seen as a single point of failure and can become severely disrupted either by disconnecting the service from the Internet or by Internet outages. These privacy issues and the susceptibility of the services to censorship are not only theoretical, but a variety of incidents have shown that these issues are readily exploited. As a consequence, it would be desirable if alternative microblogging solutions were available that offer additional privacy features and which are more resilient to censorship. In this thesis, a distributed, peer-to-peer based microblogging system consisting of mobile smartphone-equipped users that exchange messages, encrypted under a group key, in an anonymous and censorship-resistant manner is proposed, which alleviates the privacy and censorship issues of most current centralized microblogging architectures. Users conduct peer synchronizations to exchange messages, i.e., the bidirectional exchange of a prepared message buffer whenever two users are in proximity of each other and able to establish a direct link using local communication means such as Bluetooth. The way in which the send buffer is filled with messages is determined by the use of a given synchronization strategy. To show the feasibility of the proposed microblogging system, we experimentally evaluate the message spread with simulations that run on a wide range of synthetic and real-world mobility inputs. We show that such systems are working for a range of mobility and network settings, and we evaluate the effects of using different synchronization strategies. In addition to a normal operation of the network, we also test it under adversarial conditions, e.g., under the presence of users which jam the network or send spam. Since the message propagation in the purely peer-to-peer based system is dependent on the mobility the users exhibit as well as the number of users encountered, which are needed to conduct peer synchronizations, the message spread can be slow to non-existent, if parts of the network are segmented and users can not exchange messages via peer synchronizations. In such cases, the devised solution for a higher message spread is facilitated by employing a server that stores the messages of multiple groups in an Oblivious RAM (ORAM) data structure which can be accessed by users at their own discretion. On demand, users read or write their group-encrypted messages obliviously, without the server getting to know anything about the accesses that took place by the users including the message accessed or whether the access was a read or write access. In total, the microblogging solution's use is feasible, but the design decisions required for anonymity result in a delayed spread of messages on a best effort basis.

Place of Publication: Darmstadt
Divisions: 20 Department of Computer Science
20 Department of Computer Science > Security Engineering
Date Deposited: 29 Jul 2018 19:55
Official URL: http://tuprints.ulb.tu-darmstadt.de/7554
URN: urn:nbn:de:tuda-tuprints-75541
Referees: Katzenbeisser, Prof. Dr. Stefan and Armknecht, Prof. Dr. Frederik
Refereed / Verteidigung / mdl. Prüfung: 5 June 2018
Alternative Abstract:
Alternative abstract Language
Microblogging ist eine beliebte Form der Kommunikation im Bereich der Online Social Networks (OSN). Es erlaubt den Benutzern kurze, informative Nachrichten an eine Gruppe Interessierter zu versenden. Die meisten zur Zeit existierenden Diensteanbieter verwenden eine zentralisierte Client-Server-Architektur und versenden die Nachrichten unverschlüsselt. Eine sich daraus ergebende Problematik ist, dass das gesamte Nutzerverhalten überwacht werden kann und dass das serverseitige Zensieren von Nachrichten einfach durchgeführt werden kann. Zusätzlich ermöglicht die Zentralisierung des Dienstes Angriffsmöglichkeiten gegen die Verfügbarkeit, indem er vom Internet abgetrennt wird oder indem er unerreichbar durch Ausfälle des Internets wird. Diese angesprochenen Kritikpunkte hinsichtlich Privatheit sowie die Anfälligkeit für Zensur sind nicht nur eine theoretische Möglichkeit, sondern wurden durch eine Reihe von Vorfällen zur praktisch durchführbaren Realität. Aus diesen Gründen wäre es wünschenswert, alternative Microblogging-Dienste zur Verfügung zu haben, die ein Mehr an Privatheit bieten und zugleich resilienter gegenüber Zensurmaßnahmen sind. In dieser Arbeit wird ein verteiltes, peer-to-peer basiertes Microblogging-System vorgestellt, welches aus mobilen Smartphone-Nutzern besteht, die ihre Nachrichten unter einem Gruppenschlüssel verschlüsselt anonym und zensurgeschützt verbreiten können. Die Nutzer benutzen für das Verbreiten der Nachrichten Peer-Synchronisationen, d.h. es erfolgt - wann immer sich aufgrund der örtlichen Nähe zweier Nutzer die Möglichkeit ergibt einen direkten Kommunikationskanal zwischen den Smartphones aufzubauen - ein beidseitiger Austausch von vorbereiteten Nachrichtenpuffern. Die Art auf die die Nachrichtenpuffer gefüllt werden hängt dabei von einer gewählten Synchronisationsstrategie ab. Um die Durchführbarkeit des vorgeschlagenen Microblogging-Systems vorzuführen, wird die Nachrichtenverbreitung mittels Simulationen experimentell untersucht, die auf Grundlage eines breiten Spektrums von synthetischen und empirischen Bewegungsmustern der Nutzer erfolgen. Es wird gezeigt, unter welchen Bedingungen hinsichtlich Bewegungsmuster und Netzwerkeinstellungen die Nachrichtenverbreitung gelingt, inklusive der Auswirkungen von verschiedenen Synchronisationsstrategien. Neben dem ungehinderten Ablauf wird dabei auch der Betrieb unter dem Vorhandensein von Gegenspielern getestet, die das Netzwerk durch Jamming oder das Versenden von Spam unbrauchbar machen wollen. Da die Nachrichtenverbreitung in einem reinen peer-to-peer basierten System von der Bewegung der Nutzer und den daraus resultierenden Begegnungen derselben abhängig ist, kann es vorkommen, dass die durch Peer-Synchronisationen erreichte Nachrichtenverbreitung langsam erfolgt oder sogar nicht stattfinden kann, falls Teile des Netzwerks segmentiert und somit voneinander abgeschottet sind. In diesen Fällen ist es vorgesehen einen höheren Verbreitungsgrad der Nachrichten durch die Benutzung einer Server-Komponente zu erreichen, die die Nachrichten der verschiedenen Gruppen in einer Oblivious RAM (ORAM) Datenstruktur speichert. Dieser Speicher erlaubt es den Nutzern lesend oder schreibend auf ihre Nachrichten zuzugreifen, ohne dass der Server aus diesen Zugriffen irgendwelche Informationen über die Art des Zugriffs oder auf die zugegriffenen Nachrichten gewinnen kann. Das vorgestellte Microblogging-System ist nutzbar, jedoch ist die Nachrichtenverbreitung aufgrund der für die Anonymität nötigen Designentscheidungen verzögert.German
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