来源：Global Internet Freedom Consortium
The Internet has become a revolutionary force in repressive regimes. The free flow of
information and idea exchange has been perceived as a threat, rather than a blessing, by the authorities in these countries. In response, they have imposed strong censorship on Internet usage by monitoring, filtering, tracing and blocking data flows, using advanced technologies.Confined to a tailored and distorted cyberspace, innocent citizens face constant threats when they read, write or speak on the Internet, as their privacy is exposed under the authorities’watchful eyes. The consequences can be life-threatening. In this environment, the service and
content providers practice a great deal of self-censorship 1.
Since late 1990s, there have been heroic efforts from grassroots organizations to defeat the censorship, with technological counter-measures. These efforts are mostly in the form of computer and Internet technologies to evade data monitoring, circumvent data flow blocking,or defeat tracing. These technologies vary greatly from each other in their objectives, designs and implementations, and have significantly different strengths and weaknesses.
In addition, they have wide range of maturity levels and life-cycles. Some have been field-proven and in operation for many years. Some have always been in design and development mode since day one. Some stirred up quite some media hype initially but never materialized. Yet, some have been quietly and persistently running in semi-underground mode for many years with great achievements.
This article aims to provide a non-technical overview of the leading and most influential technologies used to circumvent Internet censorship in repressive regimes. We will also discuss the software packages that were found to be most effective in countering the blockage for end-users. Thus, this article will document the state of the art in this field, and provide practical guidance for users who need to make judicious choices of the best tools available for their protection.
We will use the censorship in China as the primary example because the most advanced
censorship technologies have been deployed and tested there. The circumvention tools to defeat the censorship in China will work equally well or better in other countries.