Internet Censorship: How Even Highly-Targeted Censorship Can Lead To Overblocking

Posted on December 25, 2011 by Action for Freedom — Leave a comment

By Glyn Moody | Sourced from TechDirt |

As the battle rages over SOPA and PIPA, censorship is very much on people’s minds. But there are many different kinds of censorship, operating at different levels of precision. For example, while some forms are crude and inexact, like Homeland Security’s shutdown of 84,000 sites, others are highly targeted, and designed to block in a very specific way.

That’s the case for the attempted blocking of Newzbin2 in the UK. The judge, Justice Arnold, ordered the ISP BT to take a two-stage approach (possible thanks to the pre-existing “Cleanfeed” system it had set up to block child pornography).

If an IP address matches one of those contained in the blocking list, the request to access the site is routed to a proxy server where the exact URL – the specific address including the directory and filename – is examined. If that matches too, access is denied. The judge specified this technique, rather than simply ordering the IP address to be blocked, for an important reason, which he explained in one of his rulings:

the Studios now accept that the order should refer to IP address re-routing and not IP address blocking. It appears that IP address blocking could lead to “overblocking” of sites or pages that ought not to be blocked.

However, as James Firth notes in a blog post, overblocking is still likely to occurthanks to the combination of two factors:

The first is that Newzbin will – and there’s strong evidence they have done already, several times – change their IP address. It is well known that IP addresses have all but run out. Nearly all IP addresses allocated are recycled – they’ve been in use before.

Pity the website owner who picks up Newzbin’s old IP address. Under Arnold, J’s BT ruling the new owner of the IP address would have some solace in that the URL would not match, therefore BT customers would still be able to access the website, albeit via a proxy. Re-routing via the proxy may cause some minor problems, but that’s a bit of a side issue.

In the case of Sky, [another UK ISP now blocking Newzbin2] unless Sky happen to also use a 2-stage blocking system [like BT] – and my contacts tell me they do not – then whoever picks up the old recycled IP addresses from Newzbin will find themselves blocked.

As Firth points out, one of the many worrying aspects of the Newzbin2 judgment is that there doesn’t appear to be any mechanism for removing IP addresses once they have been placed on the blocking list – even if they are no longer used by Newzbin2. Adding new ones, by contrast, is explicitly permitted:

sites “whose sole or predominant purpose is to enable or facilitate access to the Newzbin[2] website” (para 10) can find themselves blocked, again without re-application to the court. If someone creates a website explaining how to work around the block, and this website did very little else but explain how to access Newzbin, it too could be blocked.

That would lead to yet more IP addresses being added to the list, which might then be handed out again to new users as they are recycled from ephemeral sites that pop up and then disappear.

What Firth’s analysis shows is how even relatively “sophisticated” censorship systems that aim to minimize damage to other sites can lead to overblocking because not every situation can be foreseen or planned for. Now imagine what SOPA/PIPA will do.