Milad Nasr (University of Massachusetts Amherst), Hadi Zolfaghari (University of Massachusetts Amherst), Amir Houmansadr (University of Massachusetts Amherst), Amirhossein Ghafari (University of Massachusetts Amherst)

Existing censorship circumvention systems fail to offer reliable circumvention without sacrificing their users' QoS and privacy, or undertaking high costs of operation. We have designed and implemented a censorship circumvention system, called SwarmProxy (anonymized name), whose goal is to offer emph{effective censorship circumvention} to a large body of censored users, with emph{high QoS}, emph{low costs of operation}, and emph{adjustable privacy protection}. Towards this, we have made several key decisions in designing our system.

First, we argue that circumvention systems should not bundle strong privacy protections (like anonymity) with censorship circumvention. Additional privacy properties should be offered as optional features to the users of circumvention users, which can be enabled by specific users or on specific connections (perhaps by trading off QoS).

Second, we combine various state-of-the-art circumvention techniques (such as using censored clients to proxy circumvention traffic for other censored clients, using volunteer NATed proxies, and leveraging CDN hosting) to make SwarmProxy significantly resistant to blocking, while keeping its cost of operation small ($0.001 per censored client per month).

We have built and deployed SwarmProxy as a fully operational system with end-user GUI software for major operating systems. Our system has been in beta release for over a year with hundreds of users from major censoring countries testing it on a daily basis.

A key part of SwarmProxy's design is using non-censored Internet users to run volunteer proxies to help censored users. We have performed the first user study on the willingness of typical Internet users in helping circumvention operators.

We have used the findings of our user study in the design of SwarmProxy to encourage wide adoption by volunteers; particularly, our GUI software offers high transparency, control, and safety to the volunteers.

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