Privacy preserving picture sharing : Enforcing usage control in distributed on-line social networks

The problem of usage control, which refers to the control of the data after its publication, is becoming a very challenging problem due to the exponential growth of the number of users involved in content sharing. While the best solution and unfortunately the most expensive one to cope with this particular issue would be to provide a trusted hardware environment for each user, in this paper we address this problem in a confined environment, namely online social networks (OSN), and for the particular picture sharing application. In current OSNs, the owner of an uploaded picture is the only one who can control the access to this particular content and, unfortunately, other users whose faces appear in the same picture cannot set any rule. We propose a preliminary usage control mechanism targeting decentralized peer-to-peer online social networks where control is enforced thanks to the collaboration of a sufficient number of legitimate peers. In this solution, all faces in pictures are automatically obfuscated during their upload to the system and the enforcement of the obfuscation operation is guaranteed thanks to the underlying privacy preserving multi-hop routing protocol. The disclosure of each face depends on the rules the owner of the face sets when she is informed and malicious users can never publish this content in clear even if they have access to it.