Vuvuzela is a private chat application that hides metadata, including who you chat with and when you are chatting. It supports millions of users and is secure even if the network and a majority of the servers are compromised.
Vuvuzela is built on mathematical foundations. To hide metadata, messages are routed through multiple servers, and each server adds noise. The servers add enough noise to guarantee differential privacy, a formal definition of privacy that enables users to quantify their metadata privacy after sending many messages through the system.
The research powering Vuvuzela is being conducted at MIT CSAIL and has been published in top systems conferences.
Alpenhorn is a new system developed by the Vuvuzela team that solves the problem of bootstrapping trust between users. With Alpenhorn, your username is your public key. That means you can start communicating securely with your friend knowing just their username, without needing to verify their public key and without needing to trust a single server.
A conversation in the Vuvuzela client: