1	Internet Filtering Worldwide: The Technologies of Filtering and Their Unanticipated Consequences Benjamin Edelman Berkman Center for Internet & Society Harvard Law School
2	Agenda The state of play – filtering generally Who What How Technical implementations and their unanticipated consequences Scope and overblocking
3	Country-based filtering China Saudi Arabia Vietnam United Arab Emirates Singapore United States
4	What is targeted for blocking Saudi Arabia Pornography Religions (Christianity, Judaism, and Islam too) Sensitive political content (human rights, Israel) China Western news (sometimes) Politics (Taiwan, Tibet, democracy generally) Pornography (blocked halfheartedly)
5	Filtering technologies Centralized proxy servers (Saudi Arabia) Routers & “black hole” lists (China, US) Keyword-based filtering (China) DNS redirection / “hijacking” (China)
6	Granularity of blocking Group of web servers (with adjacent addresses) Entire web server (with many sites, one IP addr) Entire web site (i.e. entire domain name) Directory on a web site Single specific web page Part of a web page Single image on a web page Part of an image
7	Granularity of blocking Group of web servers (with adjacent addresses) Entire web server (with many sites, one IP addr) Entire web site (i.e. entire domain name) Directory on a web site Single specific web page Part of a web page Single image on a web page Part of an image
8	The effect of technical happenstance on filtering granularity Proxy servers allow blocking of specific URLs Router-based filtering must block entire web servers, causing more unintended blocking (“overblocking”).
9	The effect of technical happenstance on filtering granularity Proxy servers allow blocking of specific URLs Router-based filtering must block entire web servers, causing more unintended blocking (“overblocking”). Saudi Arabia: single international gateway to Internet, relatively less Internet traffic → proxy-based filtering → relatively more granular filtering China: multiple international gateways, high traffic → router-based filtering → less granular, more overblocking (sites sharing servers, etc.)
10	Typical filtering “mistakes” Saudi Arabia blocks religioustolerance.org Encyclopedia Britannica’s “women” entry Warner Brothers Records theonion.com China blocks blogspot.com (1+ million users) Network Solutions’ main domain name redirection server, with 120,000+ customer domains … But getting more sophisticated.
11	Transparency of the block list Users cannot inspect block lists Researchers cannot inspect block lists Like commercial filtering programs (US libraries & schools)
12	Approaches to transparency Saudi Arabia Discloses the fact of filtering Official error messages when blocked sites are requested Solicits users’ suggestions and problem reports
13	Approaches to transparency China Sometimes denies the fact of filtering (“just a glitch”) No official error messages, just browser error screens No known procedure for receiving complaints or correcting mistakes
14	The effect of technical happenstance on filtering transparency Proxy servers “have to” provide error pages Router-based filtering “cannot” provide error pages
15	The effect of technical happenstance on filtering transparency Proxy servers “have to” provide error pages Router-based filtering “cannot” provide error pages Saudi Arabia: single international gateway to Internet, relatively less Internet traffic → proxy-based filtering → error pages, transparency China: multiple international gateways, high traffic → router-based filtering → no error pages, less transparency, official denials that Internet filtering exists, no “request a change” form
16	Internet Filtering Worldwide: The Technologies of Filtering and Their Unanticipated Consequences Research, articles, listings of specific blocked sites: http://cyber.law.harvard.edu/filtering Benjamin Edelman edelman@law.harvard.edu Berkman Center for Internet & Society Harvard Law School