Oppressive regimes and even democratic governments restrict Internet access. Existing anti-censorship systems often require users to connect through proxies, but these systems are relatively easy for a censor to discover and block. This project offers a possible next step in the censorship arms race: rather than relying on a single system or set of proxies to circumvent censorship ﬁrewalls, we explore whether the vast deployment of sites that host user-generated content can breach these ﬁrewalls. We have developed Collage, which allows users to exchange messages through hidden channels in sites that host user-generated content. Collage has two components: a message vector layer for embedding content in cover trafﬁc; and a rendezvous mechanism to allow parties to publish and retrieve messages in the cover trafﬁc. Collage uses user-generated content (e.g., photo-sharing sites) as “drop sites” for hidden messages. To send a message, a user embeds it into cover trafﬁc and posts the content on some site, where receivers retrieve this content using a sequence of tasks. Collage makes it difﬁcult for a censor to monitor or block these messages by exploiting the sheer number of sites where users can exchange messages and the variety of ways that a message can be hidden. Our evaluation of Collage shows that the performance overhead is acceptable for sending small messages (e.g., Web articles, email).
Applications use Collage to send and receive messages, by hiding these messages inside user-generated cover content (e.g., images, tweets, etc.) and publishing them on user-generated content hosts like Flickr or Twitter. At the receiver, Collage fetches the cover content from content hosts and decodes the message. By hiding data inside user-generated content as they traverse the network, Collage escapes detection by censors.
You can send us email at coll...@gtnoise.net. (Click ellipsis to get full address, or just take an educated guess.)
We have released an application demonstrating Collage. Right now, it is only recommended for use on Ubuntu Linux. Support for other systems will be coming in the next few days.
- Chipping Away at Censorship with User-Generated Content
S. Burnett, N. Feamster, and S. Vempala
USENIX Security Symposium. August 2010
USENIX Security 2010, Chipping Away at Censorship Firewalls with User-Generated Content. August 13, 2010.
In the Press and on the Web
M. Cooney, Researchers tout new weapon in Internet censorship arms race. Layer 8, Network World. July 9, 2010.
Nicole Kobie, Researchers hide censored files in Flickr photos. PC Pro. July 16, 2010.
Jim Giles, Hiding files in Flickr pics will fool Web censors. NewScientist. August 9, 2010.
Getting around Web censors with Flickr. Slashdot. August 15, 2010.
Ryan Paul, Beat censorship by hiding secret messages in Flickr photos. Ars Technica. August 18, 2010.
Hidden Truths: A new way of beating the web’s censors. The Economist. October 12, 2010.