computer science

Internet censorship circumvention

Internet censorship circumvention is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Internet censorship circumvention rather than just read about it. In short: Internet censorship circumvention is the use of various methods and tools by technically skilled users to bypass Internet censorship—the legal control or suppression of access to, publication of, or viewing of content on the Internet. Commonly used software tools include Lantern and Psiphon, which can bypass multiple types of restrictions.

Key takeaways

Internet censorship circumvention belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Internet censorship circumvention to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Internet censorship circumvention from memory before moving on to harder problems.

Reference excerpt

Internet censorship circumvention is the use of various methods and tools by technically skilled users to bypass Internet censorship—the legal control or suppression of access to, publication of, or viewing of content on the Internet. Commonly used software tools include Lantern and Psiphon, which can bypass multiple types of restrictions. Some methods evade less sophisticated blocking tools by using alternate Domain Name System (DNS) servers, false IP addresses, or address lookup systems. However, such methods become ineffective if censors block not only the DNS but also the IP addresses of restricted domains, thereby rendering a potential bypass ineffective. Other tools can tunnel the network traffic to proxy servers in jurisdictions that don't have censorship. Through pluggable transports, traffic obscuration, website mirrors, or archive sites, users can access copies of websites even in areas with Internet censorship. An "arms race" (or competition) has developed between censors and developers of circumvention software. This competition leads to two types of innovation: more sophisticated blocking techniques by censors, and less detectable tools by circumvention developers. While estimates of user adoption for circumvention tools vary, it is widely accepted that tens of millions of people use them each month. Barriers to adoption include usability issues; difficulty in finding reliable information on circumvention; limited motivation to access censored content; and risks from breaking the law.

Circumvention methods Major circumvention methods include alternate names and addresses; mirrors, caches, and copies; alternative platforms; proxying; and traffic obfuscation.

Alternate names and addresses Censorship filters may block specific domain names, using either DNS hijacking or URL filtering. Websites can sometimes be accessed through alternate names and addresses that may not be blocked. Some websites offer the same content across multiple pages or domains. If a website's DNS resolution is disrupted, but the site is not otherwise blocked, it may be possible to access the site directly by its IP address or by modifying a computer's hosts file. It may be possible to bypass DNS-based blocking by using alternative DNS servers or public recursive name servers (especially via an encrypted DNS client). Censors may block specific IP addresses. Depending on how such filtering is implemented, it may be possible to use different forms of a blocked IP address, for example, by specifying the address in a different numeral system. For example, the following URLs all access the same site, but only some browsers will recognize all forms of the URL:

http://192.0.33.8/ (dotted decimal) http://3221233928/ (decimal) http://0300.0000.0041.0010/ (dotted octal) http://0xc0002108/ (hexadecimal) http://0xc0.0x00.0x21.0x08/ (dotted hexadecimal) The Blockchain project Namecoin is an attempt to decentralize Internet namespaces beyond the control of any single entity. Decentralized namespaces enable domains to resist censorship. Discussion of the project began in 2010 with a desire to achieve names that are decentralized, secure, and human-readable.

Mirrors, caches, and copies Certain online services allow users to access content that is blocked on the Internet through cached or mirrored copies:

Cached pages: Some search engines retain copies of previously indexed webpages, or cached pages, which are often hosted by search engines; these may not be blocked. Mirror and archive sites: Copies of websites or pages may be available at mirror or archive sites such as Wayback Machine (by the Internet Archive) or Archive.today. The Docker registry image repository is an HTTP public service that has centralized storage, is application stateless, and is node scalable; the service has a performance bottleneck in the scenario of multinational uploading and downloading. The decentralized Docker registry (DDR) avoids this disadvantage of centralization. DDR uses a network-structured P2P network to store and query the mirror manifest file and blob routing; each node serves as an independent mirror repository to provide mirror uploading and downloading for the entire network. RSS aggregators: RSS aggregators such as Feedly may be able to receive and then forward RSS feeds that are blocked if accessed directly.

Alternative platforms Alternative types of Internet hosting platform can provide options for circumventing Internet censorship. Such alternatives include decentralized hosting, anonymity networks, federated platforms, providers with different policies, and darknets:

Decentralized hosting: Content creators may publish to an alternative platform that is willing to host this content. Napster was the earliest peer-to-peer (P2P) platform, but it was closed because of vulnerabilities with centralized bootstrapping. Gnutella was the first sustainable P2P platform that featured hosting by decentralization. The motto of the Freenet P2P platform is that "true freedom requires true anonymity." Later, the BitTorrent P2P protocol was developed to allocate resources with high performance and fairness. ZeroNet P2P web hosting was the first distributed hash table (DHT) system to support dynamic and updatable webpages. The YaCy P2P search engine is the leading distributed search. GNUnet is rebuilding the internet framework from the ground up for resilience technologically idealized. Anonymity networks: The Tor and Invisible Internet Project (I2P) networks result in increased willingness to host content that would otherwise be censored. However, hosting implementation and server location may cause challenges, and the content is still hosted by a single entity that can be controlled.

Federated: Semi-decentralized, federated platforms such as Nextcloud and PeerTube make it easier for users to find an instance where they are welcome. Providers with different policies: Some platforms that rely on cloud computing may have laxer terms of service (TOS). However, cloud computing does not, in principle, innovate fundamental laxness.

Proxying A variety of techniques support a user in leveraging technical proxies to circumvent Internet censorship:

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Internet censorship circumvention

Start with the simplest possible case. Write down what Internet censorship circumvention claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Internet censorship circumvention before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Internet censorship circumvention ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Internet censorship circumvention

In research: Internet censorship circumvention appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Internet censorship circumvention in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Internet censorship circumvention is common in secondary-school and first-year university syllabi. It links to neighbouring topics Circumvention, Content-control software, Internet privacy, so understanding it makes those chapters shorter.
In everyday life: Look for Internet censorship circumvention outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Internet censorship circumvention in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Internet censorship circumvention means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Internet censorship circumvention out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Internet censorship circumvention in simple terms?

Why does Internet censorship circumvention matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Internet censorship circumvention?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Internet censorship circumvention.