OSS: Using online scanning services for censorship circumvention

Abstract

We introduce the concept of a web-based online scanning service, or OSS for short, and show that these OSSes can be covertly used as proxies in a censorship circumvention system. Such proxies are suitable both for short one-time rendezvous messages and bulk bidirectional data transport. We show that OSSes are widely available on the Internet and blocking all of them can be difficult and harmful. We measure the number of round trips and the amount of data that can be pushed through various OSSes and show that we can achieve throughputs of about 100 KB/sec. To demonstrate the effectiveness of our approach we built a system for censored users to communicate with blocked Tor relays using available OSS providers. We report on its design and performance. © 2013 Springer-Verlag.