Network Operations and Internet Security Lab

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Collage: Defeating Censorship with User-Generated Content

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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 (Click ellipsis to get full address, or just take an educated guess.)

Demo Application

We have released an application demonstrating Collage. Right now, it's being used on Bitcoin trading systems, but will support other systems in the next few days.

Go to the official website here to find out more about how the demo application can help you.

Photo Donation

We have put a photo donation service online, which lets you donate your Flickr photo album to help fight censorship. Click here fore more information.

Source Code

Collage's source code is hosted on github.



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.

View a more complete list


Sam Burnett
Nick Feamster
Santosh Vempala

Last Updated on Friday, 19 August 2011 13:06