Weįind that the attacker can substantially reduce the entropy of a bottleneck We validate our attacks using experiments over the live Tor network. Our attacks are stealthy, and cannot be readily detected by a user or by Tor (b) exactly identify the guard relay(s) of a Tor user when circuit throughputĬan be observed over multiple connections, and (c) identify whether twoĬoncurrent TCP connections belong to the same Tor user, breaking unlinkability. Solely on throughput information, can (a) reduce the attacker's uncertaintyĪbout the bottleneck relay of any Tor circuit whose throughput can be observed,

We present attacks that, with high confidence and based Paper, we show that doing this leaks information about the set of Tor relays inĪ circuit (path).

Provide efficient service to users, these anonymity systems make full use ofįorwarding capacity when sending traffic between intermediate relays. That is untraceable by adversaries that control a small number of machines. Overall, our solution improves the decentralization of the Tor network, reduces trust assumptions and increases resilience against powerful adversaries like law enforcement and intelligence servicesĪnonymity systems such as Tor aim to enable users to communicate in a manner In our evaluation, we show that SmarTor produces significantly more reliable and precise measurements compared to the current measurement system. We prototyped SmarTor using Ethereum smart contracts and Intel SGX secure hardware. This system replaces the directory authorities with a smart contract and a distributed network of untrusted entities responsible for bandwidth measurements. In particular, we leverage several emerging technologies, such as blockchains, smart contracts, and trusted execution environments to design and prototype a system called SmarTor. Our work aims at distributing the work of these trusted authorities, such increasing resilience against attacks on core infrastructure components of the Tor network. This centralization is concerning since a powerful adversary might compromise these servers and conceal information about honest nodes, leading to the full de-anonymization of all Tor users. In the Tor anonymity network, the distribution of topology information relies on the correct behavior of five out of the nine trusted directory authority servers.

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