Accordingly to recent news reports (NYT, WSJ), the Chinese government has mandated that, beginning July 1, every PC sold in China must include a censorship program called Green Dam.

This software is designed to monitor internet connections and text typed on the computer. It blocks undesirable or politically sensitive content and optionally reports it to authorities. Green Dam was developed by a company called Jin Hui and is available as a free download. We examined version 3.17.

How Green Dam Works

The Green Dam software filters content by blocking URLs and website images and by monitoring text in other applications. The filtering blacklists include both political and adult content. Some of the blacklists appear to have been copied from American-made filtering software.

Image filter Green Dam includes computer vision technology used to block online images containing nudity. The image filter reportedly works by flagging images containing large areas of human skin tone, while making an exception for close-ups of faces. We've found that the program contains code libraries and a configuration file from the open-source image recognition software OpenCV.

Text filter Green Dam scans text entry fields in various applications for blocked words, including obscenities and politically sensitive phrases (for example, references to Falun Gong). Blacklisted terms are contained in three files, encrypted with a simple key-less scrambling operation. We decrypted the contents of these files: xwordl.dat, xwordm.dat, and xwordh.dat. We also found what appears to be a word list for a more sophisticated sentence processing algorithm in the unencrypted file FalunWord.lib. When Green Dam detects these words, the offending program is forcibly closed and an error image (shown above) is displayed.

URL filter Green Dam filters website URLs using patterns contained in whitelist and blacklist files (*fil.dat, adwapp.dat, and TrustUrl.dat). These files are encrypted with the same key-less scrambling operation as the blacklists for the text filter. Five of the blacklists correspond to the categories in the content filtering section of Green Dam's options dialog (shown below).

We found evidence that a number of these blacklists have been taken from the American-made filtering program CyberSitter. In particular, we found an encrypted configuration file, wfileu.dat, that references these blacklists with download URLs at CyberSitter's site. We also found a setup file, xstring.s2g, that appears to date these blacklists to 2006. Finally, csnews.dat is an encrypted 2004 news bulletin by CyberSitter. We conjecture that this file was accidentally included because it has the same file extension as the filters.

Read Full Report: Analysis of the Green Dam Censorware System

Scott Wolchok, Randy Yao, and J. Alex Halderman
Computer Science and Engineering Division
The University of Michigan

Removing Green Dam

Green Dam allows users who know its administrator password to uninstall the software. We tested the uninstaller and found that it appears to effectively remove Green Dam from the computer. However, it fails to remove some log files, so evidence of users' activity remains hidden on the system.

In light of the serious vulnerabilities we outlined above, the surest way for users to protect themselves is to remove the software immediately using its uninstall function.

China Squeezes PC Makers
Beijing Is Set to Require Web Filter That Would Censor 'Harmful' Internet Sites
http://online.wsj.com/article/SB124440211524192081.html

BEIJING -- China plans to require that all personal computers sold in the country as of July 1 be shipped with software that blocks access to certain Web sites, a move that could give government censors unprecedented control over how Chinese users access the Internet.

The government, which has told global PC makers of the requirement but has yet to announce it to the public, says the effort is aimed at protecting young people from "harmful" content. The primary target is pornography, says the main developer of the software, a company that has ties to China's security ministry and military. ...

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