  Nowadays we are faced with an increasing popularity of social software
including wikis, blogs, micro-blogs and online social networks such as Facebook
and MySpace. Unfortunately, the mostly used social services are centralized and
personal information is stored at a single vendor. This results in potential
privacy problems as users do not have much control over how their private data
is disseminated. To overcome this limitation, some recent approaches envisioned
replacing the single authority centralization of services by a peer-to-peer
trust-based approach where users can decide with whom they want to share their
private data. In this peer-to-peer collaboration it is very difficult to ensure
that after data is shared with other peers, these peers will not misbehave and
violate data privacy. In this paper we propose a mechanism that addresses the
issue of data privacy violation due to data disclosure to malicious peers. In
our approach trust values between users are adjusted according to their
previous activities on the shared data. Users share their private data by
specifying some obligations the receivers must follow. We log modifications
done by users on the shared data as well as the obligations that must be
followed when data is shared. By a log-auditing mechanism we detect users that
misbehaved and we adjust their associated trust values by using any existing
decentralized trust model.
