The Register reports: An NSA presentation released by Edward Snowden contains mixed news for Tor users. The anonymizing service itself appears to have foxed US and UK government snoops, but instead they are using a zero-day flaw in the Firefox browser bundled with Tor to track users.

“These documents give Tor a huge pat on the back,” security guru Bruce Schneier told The Register. “If I was a Tor developer, I’d be really smiling after reading this stuff.”

The PowerPoint slide deck, prepared in June last year and entitled “Tor stinks”, details how the NSA and the UK’s Government Communications Headquarters (GCHQ) have been stymied by trying to track Tor users, thanks to the strength of the open source system.

“We will never be able to de-anonymize all Tor users all the time,” the presentation states. “With manual analysis we can de-anonymize a very small fraction of Tor users, however, no success de-anonymizing a user.”

The presentation says that both the NSA and GCHQ run Tor nodes themselves (the Brits use Amazon Web Services for this under a project entitled Newton’s Cradle), but these are only a very small number in comparison to the whole system. This makes tracking users using traditional signals-intelligence methods impossible.

There’s also a case of diminishing returns as Tor becomes more popular. With each user acting as a transport node, the sheer scale of the system means it becomes steadily more difficult for the intelligence community to run enough nodes to be useful for tracking.

Bruce Schneier reports: The online anonymity network Tor is a high-priority target for the National Security Agency. The work of attacking Tor is done by the NSA’s application vulnerabilities branch, which is part of the systems intelligence directorate, or SID. The majority of NSA employees work in SID, which is tasked with collecting data from communications systems around the world.

According to a top-secret NSA presentation provided by the whistleblower Edward Snowden, one successful technique the NSA has developed involves exploiting the Tor browser bundle, a collection of programs designed to make it easy for people to install and use the software. The trick identified Tor users on the internet and then executes an attack against their Firefox web browser.

The NSA refers to these capabilities as CNE, or computer network exploitation.

The first step of this process is finding Tor users. To accomplish this, the NSA relies on its vast capability to monitor large parts of the internet. This is done via the agency’s partnership with US telecoms firms under programs codenamed Stormbrew, Fairview, Oakstar and Blarney.

The NSA creates “fingerprints” that detect http requests from the Tor network to particular servers. These fingerprints are loaded into NSA database systems like XKeyscore, a bespoke collection and analysis tool which NSA boasts allows its analysts to see “almost everything” a target does on the internet.

Using powerful data analysis tools with codenames such as Turbulence, Turmoil and Tumult, the NSA automatically sifts through the enormous amount of internet traffic that it sees, looking for Tor connections.

Last month, Brazilian TV news show Fantastico showed screenshots of an NSA tool that had the ability to identify Tor users by monitoring internet traffic.

The very feature that makes Tor a powerful anonymity service, and the fact that all Tor users look alike on the internet, makes it easy to differentiate Tor users from other web users. On the other hand, the anonymity provided by Tor makes it impossible for the NSA to know who the user is, or whether or not the user is in the US. [Continue reading…]

Everything you need to know about the NSA and Tor in one FAQ.

Reports in The Guardian and the Washington Post, and the leaked documents: Tor: ‘The king of high-secure, low-latency anonymity’ and ‘Tor stinks’.