Black Hat cancels talk on how to crack Tor

A highly anticipated talk on how to identify users of the internet privacy service Tor has been pulled from the upcoming Black Hat security conference.

The talk was cancelled at the request of attorneys for Carnegie Mellon University in Pittsburgh, where the speakers work as researchers.

Tor is a double-edged sword that has given dissidents living under repressive regimes a way of communicating safely. But it also has 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 for Las Vegas August 6-7.

A Black Hat spokesperson 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 US Defense Department. SEI also runs CERT, the Computer Emergency Response Team, which works with the US Department of Homeland Security on major cybersecurity issues.

Spokesmen for Carnegie Mellon and the Defense Department did not comment on the cancellation. One official said DHS had played no role in pulling the talk.

The talk's abstract, titled “You don’t have to be the NSA to Break Tor: De-Anonymising 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 US 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 US 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 US 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-anonymise hundreds of thousands Tor clients and thousands of hidden services within a couple of months,” all for less than US$3000. Neither man responded to a request for comment.

Their 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, US authorities in October shut down online drug bazaar Silk Road, a so-called hidden service reachable only via Tor.

Tor project president Roger Dingledine, lead developer of the software, told an online mailing list that the project had not requested the talk be cancelled.

Dingledine said the nonprofit group was working with CERT to coordinate disclosure of details on the researchers' attack on the network.

He also said he had questions "about some aspects of the research." In years past, other researchers studying Tor traffic have been criticised for intruding on users' privacy.

This would not be the first time a talk has been cancelled at Black Hat. Presentations have been pulled from it and other conferences under pressure from software makers or for other reasons.