Anonymity networks, which sit on top of the public Internet, are designed to conceal people's Web-browsing habits from prying eyes. The most popular of these, Tor, has been around for more than a decade and is used by millions of people every day.

Recent research, however, has shown that adversaries can infer a great deal about the sources of supposedly anonymous communications by monitoring data traffic though just a few well-chosen nodes in an anonymity network. At the Association for Computing Machinery Symposium on Operating Systems Principles in October, a team of MIT researchers presented a new, untraceable text-messaging system designed to thwart even the most powerful of adversaries. Joining Zeldovich on the paper are joint first authors David Lazar, a PhD student in electrical engineering and computer science, and Jelle van den Hoof, who received his MIT PhD in the spring, and Matei Zaharia, an assistant professor of computer science and engineering and, like Zeldovich, one of the co-leaders of the Parallel and Distributed Operating Systems group at MIT's Computer Science and Artificial Intelligence Laboratory.

Vuvuzela is a dead-drop system, in which one user leaves a message for another at a predefined location -- in this case, a memory address on an Internet-connected server -- and the other user retrieves it. But it adds several layers of obfuscation to cover the users' trails. To illustrate how the system works, Lazar describes a simplified scenario in which it has only three users, named, by cryptographic convention, Alice, Bob, and Charlie. Alice and Bob wish to exchange text messages, but they don't want anyone to be able to infer that they've been in touch.

If Alice and Bob send messages to the dead-drop server, and Charlie doesn't, then an observer would conclude that Alice and Bob are communicating. So the system's first requirement is that all users send regular messages to the server, whether they contain any information or not.

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