Private messaging over the Internet has proven challenging to implement, because even if message data is encrypted, it is difficult to hide metadata about who is communicating in the face of traffic analysis. Systems that offer strong privacy guarantees, such as Dissent scale to only several thousand clients, because they use techniques with superlinear cost in the number of clients (e.g., each client broadcasts their message to all other clients). On the other hand, scalable systems, such as Tor, do not protect against traffic analysis, making them ineffective in an era of pervasive network monitoring. Vuvuzela is a new scalable messaging system that offers strong privacy guarantees, hiding both message data and metadata. Vuvuzela is secure against adversaries that observe and tamper with all network traffic, and that control all nodes except for one server. Vuvuzela’s key insight is to minimize the number of variables observable by an attacker, and to use differential privacy techniques to add noise to all observable variables in a way that provably hides information about which users are communicating. Vuvuzela has a linear cost in the number of clients, and experiments show that it can achieve a throughput of 68,000 messages per second for 1 million users with a 37-second end-to-end latency on commodity servers.
Vuvuzela is the first system to scale private messaging to millions of users and tens of thousands of messages per second,while protecting against traffic analysis by a powerful adversary who can compromise all but one of the system’s servers.
Vuvuzela achieves this through a novel approach consisting of two steps. First, Vuvuzela’s protocol is designed to clearly identify and minimize the number of observable variables
in the system. Second, Vuvuzela’s protocol hides these variables using noise with quantifiable security properties, leveraging tools from differential privacy. Together, these techniques let Vuvuzela achieve private messaging at a scale orders of magnitude higher than prior systems