Jeffrey Race

Recent articles in the Bangkok press have touched, sometimes with dry humor, on the Thai government's practice of banning access to foreign websites from within Thailand. Censorship raises troubling policy issues wherever practiced, abroad as well as here. This article sticks to technical issues, hoping to unscramble for users here the oddities of local internet censorship.

Technical Aspects

Benjamin Edelman of Harvard Law School's Berkman Center for Internet & Society recently presented two technical papers offering a taxonomy of internet censorship methodologies and an overview of their differing consequences and their varying appearances to the user (see Resources section at bottom). Edelman itemizes the four widespread methodologies as

* Proxy servers

* Router-level: by IP address of web server

* DNS server: domain name hijacking

* Packet sniffer / keyword filtering

These can be used in combination for increased effectiveness or even for increased selectivity. The important issues for users are whether they know they are being blocked from access, and whether there is "overblocking", causing sites other than those targeted by the authorities to be censored as well. If so (and leaving aside controversy about censorship itself) real damage is done to society and economy as the public are cast into unwitting and unintended darkness.

In blocking's early days, Thai ISPs received direction from several different bodies (Communications Authority of Thailand, police and others), but after numerous complaints, all official guidance now comes from the Information and Communications Technology Ministry as a periodic "BlockURL" e-mail message listing domains which each ISP must in principle apply to all customers. Official filtering is done using a caching proxy server ("transplant server") which, in the case of blocked IP addresses, serves a "request denied" page, like the following, instead of the requested page.

Of the 1,247 sites now officially blocked a few are devoted to online gaming, one incites hatred of HM the King, one belongs to a separatist movement, and the thousand-odd remaining vend pornography. (The domain names show much more creativity than the acts pictured.) No major hosting service such as Angelfire or Geocities is blocked in its entirety, so Thailand officially avoids one kind of overblocking that Edelman describes.

Some countries utilize router-level filtering which simply blocks packets either to or from an IP address (numeric counterpart to the commonly used alphanumeric domain name) depending on system configuration. IP address filtering is considered quite naughty as no "request denied" page is returned (keeping the beneficiary ignorant of the block) and it applies to an entire host: all pages are blocked even though some may be innocent and unrelated to the offending customer of the hosting service. It may be particularly difficult for the non-technical user to fathom since apparently different domains (www.virtue.com and www.naughty.com) may share the same IP address. Edelman's second paper provides the gory details.

Some countries like China use a combination of IP filtering, domain name hijacking and keyword filtering to increase the effectiveness of blocking. This requires a heavy investment of time and money and also slows packet throughput.

Piercing the Bans

Some local businesses bypass proxy caching entirely as part of their ISP contracts and so experience no blocking of officially blacklisted sites, even though they should according to policy.

Other users having legitimate reason to pierce the blocking regime can use an "anonymous browser proxy", inconvenient but effective. The famous pioneer of this service is still at <http://www.anonymizer.com/>, but access is now charged, not free. Two free services are available at the URLs shown in the Resources section; simply input the censored website's URL to the proxy's location window, press enter, and off you go. Some proxies are configurable to block cookies, images, javascript, popups and the like.

Confusing the Surfer

However as usual in Thailand nothing is as it first appears. Alongside the official mechanism, which despite the policy controversy surrounding censorship is at least transparent and clearly understood, at least one site is "mysteriously inaccessible" to large parts of the internet in Thailand. This mysterious inaccessibility crosses a new threshhold in terms of banned subject matter and cleverly confuses the websurfer since "request denied" never appears. It also provides those behind it a mechanism of plausible deniability.

This "mysterious inaccessibility" appears to employ the deprecated "cheap and dirty" IP address filtering. As the least expensive implementation requiring no added hardware, it has two serious adverse consequences. First, loss of transparency: the beneficiary of web censorship is unaware he is being blocked. Depending on his ISP's proxy configuration, he may receive such messages as "Gateway error", "Page cannot be displayed" "TCP_Error" or he may even be diverted to the new Nipa domain redirection service and end up unexpectedly at Google as shown in the accompanying examples.

The second undesirable consequence of IP filtering is its blocking of an entire host. Under the regime of "mysterious inaccessibility", several local ISPs no longer transmit packets for <http://pws.prserv.net/studies/>, which does not appear on the Ministry's BlockURL list. Just like the accused drug pusher who still ends up dead though named in no Writ of Execution, so this site is dead to a large number of local internet users, unless accessed with a browser proxy. The server, formerly run by IBM and now AT&T, hosts valuable technical download sites, all now "mysteriously inaccessible" to customers of these ISPs.

Interestingly the target "mysteriously inaccessible" site offers neither sex, nor gambling, nor politics: it details a corruption scandal involving law enforcement authorities and a state-controlled bank about which senior editors of local Thai- and English-language papers have had extensive documentation for months which curiously remains unpublished in the Bangkok press.

This may be an internet "first" for Thailand. Newspapers are now self-censored, but never before has "mysterious inaccessibility" blocked access to a foreign website detailing suspected criminal activity by those operating under state authority. With this alarming possibility in mind, local internet users may wish to sharpen their proxy skills as soon as possible.


"Internet Filtering: Technologies & Best Practices"


"Web Sites Sharing IP Addresses: Prevalence and Significance"


Anonymous browser proxies



Google search string for free anonymous browser proxy services

   {+anonymous +browser +proxy +free}

Test websites

   To test official blocking: <http://sex.com>

   To test "mysterious inaccessibility": <http://pws.prserv.net/studies/>

Technical description of Nipa's experimental service


Copyright © 2004   by Jeffrey Race      This page last updated October 3,   2004

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