OUTOPIA: private user discovery on the internet

ABSTRACTBefore being able to communicate with one another over the Internet, users in messaging applications need to discover each other and learn their IP addresses. Today, this User Discovery process is closely coupled with the communication provider. As a result, these providers are able to find (i) who is talking to whom, (ii) who is friends with whom and (iii) where is everybody located in the Internet address space at any time, even when there was no communication channel ever established, positioning this way themselves as powerful "Big Brothers". In this paper, we show that it is easy for friends to discover each other without the need of a centralised service provider that monitors each and every move they make. We propose OUTOPIA: a system to provide privacy-preserving User Discovery on the Internet. With OUTOPIA, users are able to discover each other, without revealing their social connections. We implemented a prototype of our approach and showed that it is inherently scalable, able to handle tens of thousands of users per server. Our preliminary performance results suggest that users are able to discover each other in no more than a few milliseconds, while generating negligible traffic overall.