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New HTTP error code 451 to signal censorship

Will help catalogue attempts to limit information

After a three-year campaign, the IETF has cleared the way for a new HTTP status code to reflect online censorship.

The new code – 451 – is in honor of Ray Bradbury's classic novel Fahrenheit 451 in which books are banned and any found are burned.

The idea is that rather than a web server, proxy or some other system returning a 403 code to a browser when information is blocked – i.e. you are not authorized to see it – the 451 status code will mean "unavailable for legal reasons." Specifically, according to a draft RFC:

This status code indicates that the server is denying access to the resource as a consequence of a legal demand.

The server in question might not be an origin server. This type of legal demand typically most directly affects the operations of ISPs and search engines.

The IETF published the proposal late last week; this should encourage some people to start using it early. There will be a few more steps before it becomes official. It was first proposed back in June 2012 when British ISPs started being forced to block The Pirate Bay.

That sparked a blog post that proposed a special censorship code, and in turn a campaign to make it happen.

In a post on Friday, the chairman of the relevant working group, Mark Nottingham, revealed why it had taken so long to get approval: because the powers that be at the IETF were not persuaded is was a good use of a limited number of status codes.

"Initially, I and some others pushed back," reveals Nottingham. "HTTP status codes are a constrained name space; once we use everything from 400 to 499, for example, we're out of luck. Furthermore, while 451 met many of the guidelines for new status codes (such as being potentially applicable to any resource), there wasn't any obvious way for machines to use it."


However, as time has passed, things have changed. Says Nottingham: "As censorship became more visible and prevalent on the Web, we started to hear from sites that they'd like to be able to make this distinction. More importantly, we started to hear from members of the community that they wanted to be able to discover instances of censorship in an automated fashion."

Different groups have started spidering the web to look for examples of censorship, and the 451 code makes that task significantly easier, so the engineers have come around to the idea.

Of course that does not mean to say that 451 will be used for all censorship efforts, but it does provide an official way to do so, and the IETF is hopeful that big companies like Facebook, Google and Twitter will start using it.

Nottingham also suggests that the error code could be used a way to "prompt the user to try accessing the content in a different way". For example, it could point users to the Tor network as a way to bypass censorship.

Don't expect to see 451 codes pop up in countries that routinely censor the internet, however. Typically those countries are not overly keen on letting their citizens know just how much information they are hiding from them. The code is however in the best traditions of the internet: using the network itself to gently press on efforts to control it. ®

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