Chelsea H. Komlo (University of Waterloo), Nick Mathewson (The Tor Project), Ian Goldberg (University of Waterloo)
Our USENIX Security paper is currently available.
Citation: Chelsea H. Komlo, Nick Mathewson, Ian Goldberg. "Walking Onions: Scaling Anonymity Networks while Protecting Users". 29th USENIX Security Symposium, August 2020.
We make a Docker-based simulation environment available to aid reproduceability of our results.
Scaling anonymity networks offers unique security challenges,
as attackers can exploit differing views of the
network's topology to perform epistemic and route capture attacks.
Anonymity networks in practice, such as Tor, have opted for security over
scalability by requiring participants to share a globally consistent view
of all relays to prevent these kinds of attacks.
Such an approach requires each user to maintain up-to-date information about every
relay, causing the total amount of data each user must download
every epoch to scale linearly with the number of relays. As the number
of clients increases, more relays must be added to provide bandwidth,
further exacerbating the total load on the network.
In this work, we present Walking Onions, a set of protocols improving
scalability for anonymity networks. Walking Onions enables constant-size scaling of the
information each user must download in every epoch, even as the number of relays in the network grows.
Furthermore, we show how
relaxing the clients' bandwidth growth from constant to logarithmic can enable
an outsized improvement to relays' bandwidth costs.
Notably, Walking Onions offers
the same security properties as current designs that require a globally consistent
network view. We present two protocol variants. The first requires minimal
changes from current onion-routing systems. The second presents a more
significant design change, thereby
reducing the latency required to establish a path through
the network while providing better forward secrecy than previous such
constructions.
We implement and evaluate Walking Onions in a simulated onion-routing anonymity
network modelled after Tor, and validate that
Walking Onions indeed offers significant scalability improvements for
networks at or above the size of the current Tor network.
