Privacy Friendly Information Disclosure

When using electronic services, people are often asked to provide personal information. This raises many privacy issues. To gain the trust of the user, service providers can use privacy policy languages such as P3P to declare the purpose and usage of this personal information. User agents can compare these policies to privacy preferences of a user and warn the user if his privacy is threatened. This paper extends two languages: P3P and APPEL. It makes it possible to refer to certified data and credentials. This allows service providers to define the minimal level of assurance. It is also shown how different ways of disclosure (exact, blurred, verifiably encrypted, ...) can be specified to achieve more privacy friendly policies. Last, the paper describes a privacy agent that makes use of the policies to automate privacy friendly information disclosure.