In new generation social networks, we expect that the demand of tools allowing the user to effectively control privacy, without relying on the provider trustworthiness, will be more and more increasing. A lot of precious information is currently released by users with no privacy control whenever they evaluate resources, which, for example, is done in Facebook through the “Like Button”. A mechanism allowing the user to express her preferences fully preserving her privacy is thus desired, especially if it is able to protect user privacy also in case of untrustworthy social network provider. In this paper, we propose a solution to this problem, based on a DHT-based P2P social network and on a cryptographic protocol relying on partially blind digital signatures. The protocol is shown to be a solution to the trade-off between feasibility and security, since it guarantees the needed security requirements without including the complex features of existing e-voting systems.