"I am Spartacus" – privacy enhancing technologies and privacy as a public good

The paper introduces an approach to privacy enhancing technologies that sees privacy not merely as an individual right, but as a public good. This understanding of privacy has recently gained ground in the debate on appropriate legal protection for privacy in an online environment. The jurisprudential idea that privacy is a public good and prerequisite for a functioning democracy also entails that its protection should not be left exclusively to the individual whose privacy is infringed. This idea finds its correspondence in our approach to privacy protection through obfuscation, where everybody in a group takes a small privacy risk to protect the anonymity of fellow group members. We show how these ideas can be computationally realised in an Investigative Data Acquisition Platform (IDAP). IDAP is an efficient symmetric Private Information Retrieval (PIR) protocol optimised for the specific purpose of facilitating public authorities’ enquiries for evidence