Online Social Networks like Facebook, MySpace, Xing, etc. have become extremely popular. Yet they have some limitations that we want to overcome for a next generation of social networks: privacy concerns and requirements of Internet connectivity, both of which are due to web-based applications on a central site whose owner has access to all data. To overcome these limitations, we envision a paradigm shift from client-server to a peer-to-peer infrastructure coupled with encryption so that users

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... eep control of their data and can use the social network also locally, without Internet access. This shift gives rise to many research questions intersecting networking, security, distributed systems and social network analysis, leading to a better understanding of how technology can support social interactions. This paper is an attempt to identify the core functionalities necessary to build social networking applications and services, and the research challenges in realizing them in a decentralized setting. In the tradition of research-path defining papers in the peer-to-peer community [5, 14] , we highlight some challenges and opportunities for peer-to-peer in the era of social networks. We also present our own approach at realizing peer-to-peer social networks.