Exploring Decentralization Dimensions of Social Network Services: Adversaries and Availability

Current online Social Network Services (SNS) are organized around a single provider and while storage and functionality can be distributed, the control over the service belongs to one central entity. This structure raises privacy concerns over the handling of large-scale and at least logically centralized collections of user data. In an effort to protect user privacy and decrease provider dependence, decentralization has been proposed for SNS. This decentralization has effects on availability, opportunities for traffic analysis, resource requirements, cooperation and incenctives, trust and accountability for different entities, and performance. In this paper, we explore the spectrum of SNS implementations from centralized to fully decentralized and several hybrid constellations in between. Taking a systematic approach of SNS layers, decentralization classes, and replication strategies, we investigate the design space and focus on two issues as concrete examples where the contrast of extreme ends of the decentralization spectrum is illustrative, namely potential adversaries and churn-related profile availability. In general, our research indicates that hybrid approaches deserve more attention as both centralized as well as entirely decentralized systems suffer from severe drawbacks