Princeton boffins sniff Tor users' IDs from TCP ACKs and server sweat

The onion's getting more transparent by the day

Tor is regularly recommended as a vital privacy protection technology, and just as regularly, researchers discover ways to de-anonymise users, and the latest of these has just hit Arxiv.

The research, led by boffins from Princeton, demonstrates ways to de-anonymise Tor users with access to just one end of a communication path, at the Autonomous System (AS) level.

The attack suite, which the researchers call Raptor, differs from previous attacks against anonymity, most of which need to observe traffic flows at different points of the Tor network, and need to capture symmetric flows.

Instead, the Princeton crew proposes an asymmetric model which they call a “form of end-to-end timing analysis that allows AS-level adversaries to compromise the anonymity of Tor users … as long as the adversary is able to observe any direction of the traffic at both ends of the communication”.

This, they write, create four scenarios where an attacker might be able to collect enough information to de-anonymise a user:

  • Observing data traffic from the client to the entry relay, and from the exit relay to the server;
  • Observing traffic from the client to the entry relay, and catching TCP ACKs from the server to the exit relay;
  • Catching TCP ACKs from a guard relay to a client, as well as data traffic from the exit relay to the server; or
  • Relying just on two sets of TCP ACKs: from the guard relay to the client, and from the server to the exit relay.

In their experimental results, the researchers reckon they achieved “detection accuracy of 95 per cent”, with other techniques available to increase this further.

The researchers' experiments used PlanetLab nodes to act as the clients and the servers, with 50 running as Tor clients and 50 running as Web servers hosting a 100 MB image file. 300 seconds' worth of packet traces for each end were analysed to get TCP sequence number and ACK number fields.

Their ability to correlate the two ends of the communication using only sequence number and ACK number ran between 94 and 96 per cent, the researchers claim.

The paper points out that a state-level attacker – that is, an NSA demanding traffic analysis from a provider – would only need traffic capture from a relatively small number of providers. “Large networks such as NTT or Level3 are able to see Tor traffic for up to 90 per cent of Tor circuits”, the paper states.

The researchers say attacks can be mitigated in two ways: the Tor network needs to monitor the routing control plane and data plane to try to detect attacks; and with a variety of preventative measures.

Preventative measures include writing Tor clients to favour guard relays that have the shortest AS path to the client; the implementation of secure inter-domain routing (which unfortunately requires a bunch of providers to agree to deploy it); and to get Tor relays advertising /24 prefixes. ®

Other stories you might like

  • GPL legal battle: Vizio told by judge it will have to answer breach-of-contract claims
    Fine-print crucially deemed contractual agreement as well as copyright license in smartTV source-code case

    The Software Freedom Conservancy (SFC) has won a significant legal victory in its ongoing effort to force Vizio to publish the source code of its SmartCast TV software, which is said to contain GPLv2 and LGPLv2.1 copyleft-licensed components.

    SFC sued Vizio, claiming it was in breach of contract by failing to obey the terms of the GPLv2 and LGPLv2.1 licenses that require source code to be made public when certain conditions are met, and sought declaratory relief on behalf of Vizio TV owners. SFC wanted its breach-of-contract arguments to be heard by the Orange County Superior Court in California, though Vizio kicked the matter up to the district court level in central California where it hoped to avoid the contract issue and defend its corner using just federal copyright law.

    On Friday, Federal District Judge Josephine Staton sided with SFC and granted its motion to send its lawsuit back to superior court. To do so, Judge Staton had to decide whether or not the federal Copyright Act preempted the SFC's breach-of-contract allegations; in the end, she decided it didn't.

    Continue reading
  • US brings first-of-its-kind criminal charges of Bitcoin-based sanctions-busting
    Citizen allegedly moved $10m-plus in BTC into banned nation

    US prosecutors have accused an American citizen of illegally funneling more than $10 million in Bitcoin into an economically sanctioned country.

    It's said the resulting criminal charges of sanctions busting through the use of cryptocurrency are the first of their kind to be brought in the US.

    Under the United States' International Emergency Economic Powers Act (IEEA), it is illegal for a citizen or institution within the US to transfer funds, directly or indirectly, to a sanctioned country, such as Iran, Cuba, North Korea, or Russia. If there is evidence the IEEA was willfully violated, a criminal case should follow. If an individual or financial exchange was unwittingly involved in evading sanctions, they may be subject to civil action. 

    Continue reading
  • Meta hires network chip guru from Intel: What does this mean for future silicon?
    Why be a customer when you can develop your own custom semiconductors

    Analysis Here's something that should raise eyebrows in the datacenter world: Facebook parent company Meta has hired a veteran networking chip engineer from Intel to lead silicon design efforts in the internet giant's infrastructure hardware engineering group.

    Jon Dama started as director of silicon in May for Meta's infrastructure hardware group, a role that has him "responsible for several design teams innovating the datacenter for scale," according to his LinkedIn profile. In a blurb, Dama indicated that a team is already in place at Meta, and he hopes to "scale the next several doublings of data processing" with them.

    Though we couldn't confirm it, we think it's likely that Dama is reporting to Alexis Bjorlin, Meta's vice president of infrastructure hardware who previously worked with Dama when she was general manager of Intel's Connectivity group before serving a two-year stint at Broadcom.

    Continue reading
  • Lithium production needs investment to keep pace with battery demand
    Report says $42b will need to be poured into industry over next decade

    Growing demand for lithium for batteries means the sector will need $42 billion of investment to meet the anticipated level of orders by the end of the decade, according to a report.

    Lithium is used in batteries that power smartphones and laptops, but there is also rising use in electric vehicles which is putting additional pressure on supplies.

    The report, Benchmark Mineral Intelligence, predicts that demand will reach 2.4 million tons of lithium carbonate equivalent by 2030, roughly four times the 600,000 tons of lithium forecast to be produced this year.

    Continue reading
  • Cars in driver-assist mode hit a third of cyclists, all oncoming cars in tests
    Still think we're ready for that autonomous future?

    Autonomous cars may be further away than believed. Testing of three leading systems found they hit a third of cyclists, and failed to avoid any oncoming cars.

    The tests [PDF] performed by the American Automobile Association (AAA) looked at three vehicles: a 2021 Hyundai Santa Fe with Highway Driving Assist; a 2021 Subaru Forester with EyeSight; and a 2020 Tesla Model 3 with Autopilot.

    According to the AAA, all three systems represent the second of five autonomous driving levels, which require drivers to maintain alertness at all times to seize control from the computer when needed. There are no semi-autonomous cars generally available to the public that are able to operate above level two.

    Continue reading

Biting the hand that feeds IT © 1998–2022