The U.S. National Security Agency has repeatedly tried to compromise Tor, the government-funded online anonymity tool, but has had little success, according to a new report in the U.K.'s Guardian.
The NSA has tried multiple strategies for defeating Tor, with its most successful method focused on attacking vulnerable software on users' computers, including the Firefox browser, according to the report, published Friday. In the Firefox attack, NSA agents have been able to gain "full control" of targets' computers, said the report, citing documents given to the Guardian by former NSA contractor Edward Snowden.
NSA documents provided by Snowden, which the Guardian began publishing in June, say the agency is collecting bulk phone records in the U.S. as well as Internet communications overseas.
But in many cases, the NSA has been frustrated in its efforts to target Tor users, an irony because the open-source project is largely funded by the U.S. Department of Defense, the NSA's parent agency, and the U.S. Department of State.
"We will never be able to de-anonymize all Tor users all the time," according to one NSA document quoted by the Guardian. "With manual analysis we can de-anonymize a very small fraction of Tor users." The NSA has had "no success de-anonymizing a user in response" to a specific request, the document said.
Tor routes Internet traffic through a number of relays as a way to keep communications anonymous. The State Department promotes the software to activists in countries with strong censorship regimes, including Iran and China.
An NSA spokeswoman referred a request for comments on the story to a previous statement from the agency:
"In carrying out its signals intelligence mission, NSA collects only those communications that it is authorized by law to collect for valid foreign intelligence and counterintelligence purposes, regardless of the technical means used by those targets or the means by which they may attempt to conceal their communications. ... It should hardly be surprising that our intelligence agencies seek ways to counteract targets' use of technologies to hide their communications.
"Throughout history, nations have used various methods to protect their secrets, and today terrorists, cybercriminals, human traffickers and others use technology to hide their activities," the statement continued. "Our intelligence community would not be doing its job if we did not try to counter that."
The NSA documents provided by Snowden detail what the Guardian story calls "proof-of-concept attacks" on Tor. One technique is for the agency to look for patterns in the signals entering and leaving the Tor network, then trying to de-anonymize users. The documents also discuss the NSA secretly operating computer nodes in the Tor network, but the success of that effort was "negligible" because the agency has access to few nodes.
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