As online social network (OSN) providers such as Facebook deal with tremendous amounts of user information, they can obtain a deep insight into their users’ personal opinions, social relationships, and economical or political preferences, raising severe privacy and security concerns. Facebook, for example, recently reached the one billion user mark and already controls the personal data of more than 10% of the world’s population. Yet, the hunt for user data is not over and users are often helpless when imposed with changes of any kind, as demonstrated by Facebook’s recent acquisition of the Instagram user base with a billion-dollar agreement. Moreover, centralized control often results in the misuse of user data. For example, LinkedIn leaked millions of passwords of its users, and the Facebook Beacon application passed sensitive shopping information of users to Facebook without their consent.

While it remains to be seen whether OSN providers would give up a major source of income and grant comprehensive security and privacy means to their users (e.g., encryption of data), decentralized OSNs are becoming more promising for better user data security and privacy. Instead of relying on a central data repository, a decentralized OSN can allow users to regain control over their data. For instance, users can encrypt their data according to their own need, enforce access control of their data at their discretion, or distribute their data to their designated storage facilities or user devices across the OSN.

With SOUP, we design and evaluate a data placement solution for decentralized OSNs that makes all data of all users available at all times in the absence of a central OSN provider. Whereas one might consider classical peer-to-peer (P2P) data storage approaches, the distributed OSN requires a unique data placement solution for a number of reasons. First, the online patterns of OSN users are much more bursty than those in traditional decentralized applications. Second, social networking platforms are increasingly employed by mobile devices, whose storage capacity is often meager. Third, an OSN needs to be robust as a whole to ensure all data of interest are highly available, including those from users who are not active or contributing.

Recently, researchers have proposed a wide range of alternative systems that consider the characteristics of an OSN in their design. In particular, different from the tit-for-tat in classical P2P networks, the inherent social relation among OSN users offers potential incentives for users to host data for each other. While some of these solutions provide means to realize data storage in decentralized OSNs, each introduces new shortcomings, ranging from technical and economical deployability issues to limited robustness and discrimination of users due to a dependency on nodes to which the user is connected in the social graph.


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Source code added!