Via CDT and PKD, both of which were briefly blocked in China this week, a Wired article from a dissident Chinese blogger discussing filter- and firewall-evasion techniques.:

The authorities have numerous ways to squelch digital dissent. ISPs maintain lists of forbidden words, including the date of the infamous Tiananmen Square massacre June 4 (六四), freedom of speech (言论自由), Falungong (法轮功), former leader Jiang Zemin (江泽民), and Jiang Yanyong (蒋彦永), the doctor who first revealed the SARS crisis in 2003. They use filtering software to block posts containing these words or to replace them with asterisks. Posts that circumvent the filters are deleted, either by ISP employees or by the government’s own Net police. Earlier this year, the authorities announced that all domestic Web sites operating without explicit government approval - including some 600,000 blogs - must register or face being blocked and shut down. More than 75 percent have complied so far. Many of those who resist have their pages hosted abroad on TypePad or Blogger. Still, the authorities often block their domain names and IP addresses, so people outside China can read their work but people inside can’t.

For every advance in censorship, bloggers find a way around it. We replace banned words with Chinese characters that sound the same when spoken but have a different meaning when written, or we transliterate them into Roman characters. Recently I came up with another technique: After the authorities blocked one of my entries, I reposted it with the characters aligned vertically instead of horizontally. The filter couldn’t recognize the words, but anyone reading them could.

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