Tor users captured by CMU had 'no reasonable expectation of privacy'

This image was removed due to legal reasons.

Two years ago, researchers affiliated with Carnegie Mellon University bragged that they had "broken" Tor, software designed to allow people to use and browse the web more privately. The revelation threw the privacy and security community into a tizzy, as the researchers claimed to have de-anonymized "hundreds of thousands" of Tor users and hidden services, which would include people who specifically used Tor to prevent their identities from being discoverable.


But then, in the midst of the uproar, the researchers, Michael McCord and Alexander Volynkin, went silent. Their talk at a security conference was canceled. And CMU refused to say anything more about the researchers' Defense Department-funded project. Many experts speculated that their research had been handed over to the feds and that they had been asked to keep quiet about it so that they didn't compromise ongoing investigations into people using the darker, illegal corners of the web.

In a court filing made public this week, we finally have confirmation that the government is indeed using the fruits of the CMU Tor hack to prosecute people. Joseph Cox of Motherboard posted a judicial order from a federal case in Washington, in which 27-year-old Brian Farrell is accused of selling drugs on Silk Road 2.0. From the order:

The record demonstrates that the defendant’s IP address was identified by the Software Engineering Institute (“SEI”) of Carnegie Mellon University (CMU”) when SEI was conducting research on the Tor network which was funded by the Department of Defense. The government previously produced information to the defense that Farrell’s IP address was observed when SEI was operating its computers on the Tor network. This information was obtained by law enforcement pursuant to a subpoena served on SEI-CMU.


Interestingly, the government got the information just with a subpoena, not with a warrant, which needs to be signed by a judge.

Farrell's attorney wanted the government to reveal more information about SEI-CMU's relationship with the government and the methods used to identify his IP address, but the judge turned Farrell down. Judge Richard Jones said the government has revealed enough information, and that Farrell can't invoke his Fourth Amendment rights against unreasonable search and seizure to argue for more information, because Tor users don't have a reasonable expectation of privacy around their IP address when they use the network.

Jones could have ruled that the Fourth Amendment was irrelevent because the invasive work was done by academic researchers not the government (though that would be complicated by the fact that they were funded by the government). But instead, he said the Fourth Amendment doesn't apply because Tor users are using a system that is fundamentally not private, according to Jones, because it exposes their IP addresses to strangers' computers. Writes Jones:

It is the Court’s understanding that in order for a prospective user to use the Tor network they must disclose information, including their IP addresses,to unknown individuals running Tor nodes, so that their communications can be directed toward their destinations.

Under such a system, an individual would necessarily be disclosing his identifying information to complete strangers. Again, according to the parties’ submissions, such a submission is made despite the understanding communicated by the Tor Project that the Tor network has vulnerabilities and that users might not remain anonymous.

Under these circumstances Tor users clearly lack a reasonable expectation of privacy in their IP addresses while using the Tor network. In other words,they are taking a significant gamble on any real expectation of privacy under these circumstances.


In other words, people who use Tor because they are interested in more privacy than offered by a normal Web browser, like Chrome, Firefox or Safari, don't legally have more privacy because of the architecture of Tor. Per the third party doctrine, you don't have privacy rights around information you hand over to a third party. Tor passes a user's request through three different nodes to its final destination in order to obscure where the request originates. In Farrell's case, the CMU researchers controlled one or more of the nodes, so were able to unmask his real starting location.

It's not the first time a judge has reached this conclusion.

Update: In a response to the ruling, Tor founder Roger Dingledine wrote that the court "does not understand how the Tor network works" and that IP information "gets stripped from messages as they pass through Tor's private network pathways." Dingledine writes that the CMU attackers did not just grab the IP address but also "intercepted and tampered with the user's traffic elsewhere in the network… They needed to attack both places in order to link the user to his destination." So it's not as simple as the judge described. Dingledine also bristled at the judge's description of Tor as a flaky network, where anonymity is far from assured.


"The Tor network is secure and has only rarely been compromised," wrote Dingledine.


This is the problem with privacy in the courts. Whether it's protected hinges not only on technological tools that we use without totally understanding how they work, but on squishy words like "reasonable." According to court decisions thus far, it is not reasonable to expect that when you use Tor to hide your IP address while surfing websites online, your IP address will actually be hidden.

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