* Introduction

The Internet is getting more and more centralized with users' personal data
hosted on servers of large service providers, which involves serious privacy
concerns. As in most cases these systems do not provide end-to-end
confidentiality, server operators have full access to user data and users are
often unaware of how much data is stored about them or with whom their data is
shared with. Such systems include email and instant messaging services like
GMail and GTalk, social network services like Facebook, Google+ and Twitter, or
file storage and sharing services like Dropbox.

It is possible to implement social sharing and messaging in a privacy protecting
way. Chapter 2 describes previous attempts at this by federated social networks,
problems with that approach and our requirements for secure communication.

We suggest a peer-to-peer architecture as a better basis for a social network
system in Chapter 3. We show how social interactions would work in such
a network while maintaining privacy of users.

In Chapter 4 we introduce core concepts of PSYC and show how we integrated it
with P2P technology provided by the GNUnet framework, and tell more about
implementation details of the prototype of Secure Share.

Chapter 5 describes the clients we have implemented and shows extension
possibilities of Secure Share.