The paper was submitted for the course of Information Systems Mass Attack and Defence at Tallinn University of Technology. December, 2011
1. Introduction. The essence of censorship
Censorship possibly is as old as a political system itself. The evil side of politics (and the latter always has the former) dictates the suppression of opponents.
According to Merriam-Webster dictionary, censorship is to examine communication/expression or resource in order to suppress or delete content if it is objectionable .
Censorship is an endless “catch me if you can” game. Innovation brings the censorship victims one step ahead of censors and the internet also did. In “traditional”, pre-internet terms censorship can be an exclusion of content from newspaper or TV program. It mainly (but not necessarily) concerns the content, but not the source. As for internet censorship, oppressing the source is more common.
Censorship can be dictated by not only political but also by social or cultural norms. Internet censorship, which in technical terms is content filtering, can be employed by public institution (schools, libraries. . .), private enterprises, end users (so called, client-side filtering, for example, parental control). In some circumstances, it can be considered ethical and legalized (filtering porn).
Censorship can exist anywhere with varying degrees, but there is a correlation between political systems and censorship: the more democratic a political system is the less chance exists for any kind of censorship there.
2. More on internet censorship
Internet censorship roughly includes the following activities: blocking web resources, suppressing freedom of expression online, monitoring online activities of users, suppress access to internet or not allowing internet connection at all.
Censorship has its side effects on whole society. One of them is self-censorship. Authoritarian governments can arrest one dissident to serve a showcase. In China, a lot of people avoid posting controversial comments or doing any politically objectionable activities online. They are just afraid. In some situations, self-censorship works better than actual censorship techniques.
Internet censorship geographic distribution (Fig.1 ) roughly coincides map of authoritarian/democratic regimes (Fig.2 ). China is the most prominent online censor in the world, but not the worst censorship case. North Korea does not have internet connection at all (only some high ranking officials have access to the internet) and the population can access only countrywide intranet which is totally controlled by the government. At the same time, computers are available only in educational institutions.
Another heavy case of internet censorship is Iran, which is suppressing any objectionable political activities online. Arrests are common. Iran is also planning to build an intranet like North Korea to further their efforts of political suppression.
But China is the most technically sophisticated censor of the world. The Great China Firewall (official name Golden Shield Project) along with various other software/hardware filtering schemes is built by Chinese government. On the other hand there are a lot of tools and workarounds to avoid the filtering. But arrests of bloggers, permanent monitoring and atmosphere of fear tears down the call for freedom in most of the Chinese users.
Internet censorship is well-known for democratic states too. But reasons are rather ethical or provoked by national security than political. In the USA, internet is not censored in its common understanding. But traffic can be monitored (automatically by machines/computers) for suspicious activities or security agencies can have broader than usual powers.
3. Types of internet filtering
There are several technical implementations of online censorship. They vary in terms of sophistication (including number and quality of personnel needed), supposed results (depends what should be censored) and of course, costs.
The differences between internet filtering mechanisms stipulate where actually internet filtering is taking place – at users’ computers, at ISP level or at the international internet gateway of the country.
So called in-line filtering (HTTP proxies , TCP/IP header/content filtering , various hybrid approaches ) can be placed anywhere between the user and web resources. In this case, ISP takes main operational responsibility for filtering. To be more reliable, filtering should happen on so called choke point – location where all communications (which are supposed to be filtered) should go through.
If filtering mechanisms will be positioned on international internet gateway, then ISPs have fewer responsibilities. Special government agency can take care of censorship. DNS tampering  filtering method is usually placed on gateway. განვაგრძოთ კითხვა “Price of Internet Censorship”