By Joseph Menn
SAN FRANCISCO (Reuters) - A highly anticipated talk on how to identify users of the Internet privacy service Tor was withdrawn from the upcoming Black Hat security conference, a spokeswoman for the event said on Monday.
The talk was canceled at the request of attorneys for Carnegie Mellon University in Pittsburgh, where the speakers work as researchers, the spokeswoman, Meredith Corley, told Reuters.
Tor is a double-edged sword that has given dissidents living under repressive regimes a way of communicating safely. But it has also enabled criminals to take advantage of its cloak of anonymity.
The Black Hat conference, one of the longest running and best-attended security trade shows in the world, is scheduled to take place in Las Vegas Aug. 6-7.
Corley said a Carnegie Mellon attorney informed Black Hat that one of the speakers could not give the Tor talk because the materials he would discuss have not been approved for public release by the university or the Software Engineering Institute (SEI).
It was unclear what aspects of the research concerned the university.
The institute, based at the university, is funded by the Defense Department. SEI also runs CERT, historically known as the Computer Emergency Response Team, which works with the Department of Homeland Security on major cybersecurity issues.
Spokesmen for Carnegie Mellon and Homeland Security had no immediate comment on the talk's cancellation.
Its abstract, titled "You don't have to be the NSA to Break Tor: De-Anonymizing Users on a Budget," had attracted attention within the security and privacy communities. The abstract had been published on Black Hat's website but has since been removed.
The U.S. government funded the creation and much of the operation of Tor as a communications tool for dissidents in repressive countries. But Tor has frustrated the U.S. National Security Agency for years, according to documents released by former agency contractor Edward Snowden.
That revelation has helped increase adoption by those seeking privacy for political reasons as well as criminals, researchers say.
Some criminal suspects on Tor have been unmasked by the U.S. Federal Bureau of Investigation and other law enforcement or intelligence agencies using a variety of techniques, including tampering with software often used alongside Tor.
In their now-vanished Black Hat abstract, researchers Alexander Volynkin and Michael McCord, said "a determined adversary" could "de-anonymize hundreds of thousands Tor clients and thousands of hidden services within a couple of months," all for less than $3,000.
The summary said they had tested their techniques and that they would discuss dozens of successes, including cases where suspected child pornographers and drug dealers had been found.
In the best-known Tor case, U.S. authorities in October shut down online drug bazaar Silk Road, a so-called hidden service reachable only via the service.
This would not be the first time a talk has been canceled at Black Hat. Presentations have been pulled from it and other conferences under pressure from software makers or for other reasons.
(Reporting by Joseph Menn; Editing by Chris Reese and Jonathan Oatis)