Encrypted networks: Secret NSA documents show campaign against Tor encrypted network - by Barton Gellman, Craig Timberg and Steven Ric

On Nov. 1, 2007, the National Security Agency hosted a talk by Roger Dingledine, principal designer of one of the world’s leading Internet privacy tools. It was a wary encounter, akin to mutual intelligence gathering, between a spy agency and a man who built tools to ward off electronic surveillance.

According to a top secret NSA summary of the meeting, Dingledine told the assembled NSA staff that his service, called Tor, offered anonymity to people who needed it badly — to keep business secrets, protect their identities from oppressive political regimes or conduct research without revealing themselves. To the NSA, Tor was offering protection to terrorists and other intelligence targets.

Beginning at least a year before Dingledine’s visit, the NSA had mounted increasingly successful attacks to unmask the identities and locations of Tor users, according to documents provided by former agency contractor Edward Snowden.

In some cases, the NSA has succeeded in blocking access to the anonymous network, diverting Tor users to insecure channels. With a tool called MJOLNIR — the name of the hammer used by Thor, the Norse god of thunder — it has been able to monitor and control the paths of communications that are supposed to be chosen randomly as they pass through Tor. Another operation, called MULLENIZE, can “stain” anonymous traffic as it enters the Tor network, enabling the NSA to identify users as it exits.

Read more: Secret NSA documents show campaign against Tor encrypted network - The Washington Post