Metadata absolutely tells you everything about somebody's life
— Stewart Baker, former General Counsel of the NSA
We kill people based on metadata
— Michael Hayden, former Director of the NSA
Vuvuzela
Vuvuzela is a messaging system that protects the privacy of message contents
and message metadata. Users communicating through Vuvuzela do not reveal who
they are talking to, even in the presence of powerful nation-state adversaries.
Our SOSP 2015 paper explains
the system, its threat model, performance, limitations, and more. Our
SOSP 2015 slides give
a more graphical overview of the system.
Vuvuzela is the first system that provides strong metadata privacy while
scaling to millions of users. Previous systems that hide metadata using
Tor (such as Pond) are prone to traffic
analysis attacks. Systems that encrypt metadata using techniques like
DC-nets and PIR don't scale beyond thousands of users.
Vuvuzela uses efficient cryptography (NaCl) to hide as
much metadata as possible and adds noise to metadata that can't be encrypted
efficiently. This approach provides less privacy than encrypting all of the
metadata, but it enables Vuvuzela to support millions of users. Nonetheless,
Vuvuzela adds enough noise to thwart adversaries like the NSA and guarantees
differential privacy for
users' metadata.
Screenshots
A conversation in the Vuvuzela client
In practice, the message latency would be around 20s to 40s, depending
on security parameters and the number of users connected to the system.
Noise generated by the Vuvuzela servers
Vuvuzela is unable to encrypt two kinds of metadata: the number of idle users
(connected users without a conversation partner) and the number of active users
(users engaged in a conversation). Without noise, a sophisticated adversary
could use this metadata to learn who is talking to who. However, the Vuvuzela
servers generate noise that perturbs this metadata so that it is difficult to
exploit.
Acknowledgements
This code is written by David Lazar with contributions from
Jelle van den Hooff, Nickolai Zeldovich, and Matei Zaharia.