关键词: 社交网, 半去中心化, 隐私保护, 访问控制

Abstract: This paper presents a privacy preserving scheme based on semi-decentralization.In this scenario，social networks sites only provide basic application services while users’ resources are managed by themselves in the client side.Users clarify the relationship types with their direct friends to the relationship server，authorized users are denoted in terms of relationship types and depth，relationship paths between owner and requestor are checked out by relationship server.Only the requestor who meets the access rules can grant access to a resource.Thus the users’ resources privacy from unauthorized access is protected in social networks.

Key words: social networks, semi-decentralization, privacy preserving, access control