In order to help people keeping control over personal data, the Caliopenproject intend to associate with each element of it's user interface,including messages, a "Privacy index" showing as precisely as possible howmuch that element is at risk of being publicly exposed. We will expose hereour problems and leads. The confidentiality of correspondence has been historically characterized byletter exchanges. Think of the stamped royal letter protected with a wax seal.Everyone knows that a letter mailed in a glued envelope is more private than astandard postcard. This confidentiality with easily-understood privacyindicators has disappeared with the advent of digital correspondence. In order to offer the public a better control over their private life,Caliopen proposes to associate a "privacy index" indicator to each element ofit's interface. The user will be able to easily improve the level indicated bythis index and thus be encouraged to better protect themselves and theircontacts. In order to do so, we have to define precise metrics to calculate thoseindices, that rely as much on technical data (protocol used, encryption...)than on human behaviour. We intend to present how much ambitious this is, thedifficulties we face, and the leads we follow to realize that particular goal.