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Internet censorship circumvention

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Title: Internet censorship circumvention  
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Subject: Censorship, Content-control software, Internet censorship, Psiphon, Internet censorship in Syria
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Internet censorship circumvention

Internet censorship circumvention describes various processes used by Internet users to bypass the technical aspects of Internet filtering and gain access to otherwise censored material.

Circumvention is an inherent problem for those wishing to censor the Internet, because filtering and blocking do not remove content from the Internet and as long as there is at least one publicly accessible uncensored system, it will often be possible to gain access to otherwise censored material. However, circumvention may not be very useful to non-tech-savvy users and so blocking and filtering remain effective means of censoring the Internet for many users.[1]

Different techniques and resources are used to bypass Internet censorship, including cached web pages, web mirrors, and archive sites, alternate DNS servers, proxy websites, virtual private networks, sneakernets, and circumvention software tools. Solutions have differing ease of use, speed, security, and risks. Most, however, rely on gaining access to an Internet connection that is not subject to filtering, often in a different jurisdiction not subject to the same censorship laws.[2] According to GlobalWebIndex, over 400 million people use virtual private networks to circumvent censorship or for increased level of privacy.[3]

There are risks to using circumvention software or other methods to bypass Internet censorship. In some countries individuals that gain access to otherwise restricted content may be violating the law, and if caught can be expelled from school, fired from jobs, jailed, or subject to other punishments and loss of access.[4]


  • Circumvention, anonymity, risks, and trust 1
  • Methods 2
    • Cached Pages 2.1
    • Mirror and archive sites 2.2
    • Web to E-mail services 2.3
    • RSS aggregators 2.4
    • IP addresses and domain names 2.5
    • Alternative DNS Servers 2.6
    • Proxy websites 2.7
    • Reverse Proxy 2.8
    • Virtual Private Networks (VPNs) 2.9
    • Sneakernets 2.10
    • Software 2.11
    • SSH tunneling 2.12
  • Shadow Internet and cell phone networks 3
  • Summary 4
  • See also 5
  • References 6
  • External links 7

Circumvention, anonymity, risks, and trust

Circumvention and anonymity are different. Circumvention systems are designed to bypass blocking, but they do not usually protect identities. Anonymous systems protect a user's identity. And while they can contribute to circumvention, that is not their primary function. It is important to understand that open public proxy sites do not provide anonymity and can view and record the location of computers making requests as well as the websites accessed.[5]

In many jurisdictions accessing blocked content is a serious dissident, protest, or reform groups should take extra precautions to protect their online identities.[5]

Circumvention sites and tools should be provided and operated by trusted third parties located outside the censoring jurisdiction that do not collect identities and other personal information. Best are trusted family and friends personally known to the circumventor, but when family and friends are not available, sites and tools provided by individuals or organizations that are only known by their reputations or through the recommendations and endorsement of others may need to be used. Commercial circumvention services may provide anonymity while surfing the Internet, but could be compelled by law to make their records and users' personal information available to law enforcement.[5]


There are many methods available that may allow the circumvention of Internet filtering. They range from the simple to the complex and from the trivial to the difficult in terms of implementation. Of course, not all methods will work to bypass all filters. And censorship tools and sites are themselves subject to censorship and monitoring.

Circumventing censorship using proxies gives access to international content, but doesn’t address domestic censorship and access to more local content. Nor does it offer a defense against DDoS or other attacks that target a publisher.[5][6]

Cached Pages

Some search engines keep cached pages, copies of previously indexed Web pages, and these pages are not always blocked. Cached pages may be identified with a small link labeled "cached" in a list of search results. Google allows the retrieval of cached pages by entering "cache:some-blocked-url" as a search request.

Mirror and archive sites

Copies of web sites or pages may be available at mirror or archive sites such as and the alternate sites may not be blocked.

Web to E-mail services

Web to e-mail services such as will return the contents of web pages with or without images as an e-mail message and such access may not be blocked.

RSS aggregators

RSS aggregators such as Google Reader and Bloglines may be able to receive and pass on RSS feeds that are blocked when accessed directly.

IP addresses and domain names

Alternative domain names may not be blocked. For example the following domain names all refer to the same web site: , and .

Or alternative URLs may not be blocked. For example: vs.,,,, and

Entering an IP address rather than a domain name ( or a domain name rather than an IP address ( will sometimes allow access to a blocked site.

Specifying an IP address in a base other than 10 may bypass some filters. The following URLs all access the same site, although not all browsers will recognize all forms: (dotted decimal), http://3494942722 (decimal), http://0320.0120.0230.02 (dotted octal), http://0xd0509802 (hexadecimal), and http://0xd0.0x50.0x98.0x2 (dotted hexadecimal).

Alternative DNS Servers

Using DNS servers other than those supplied by default by an ISP may bypass DNS based blocking. OpenDNS and Google offer DNS services or see List of Publicly Available and Completely Free DNS Servers.

Proxy websites

Proxy websites are often the simplest and fastest way to access banned websites in censored nations. Such websites work by being themselves un-blocked, but capable of displaying the blocked material. This is usually accomplished by entering a URL which the proxy website will fetch and display. Using the

Translation services such as and are a specific type of proxy website and can sometimes be used to display blocked pages even when no translation is needed by asking for a translation into the same language that is used on the original site or by asking for a translation from a language that does not appear on the original site.

The mobile Opera Mini browser uses a proxy-based approach employing encryption and compression in order to speed up downloads. This has the side effect of allowing it to circumvent several approaches to Internet censorship. In 2009 this led the government of China to ban all but a special Chinese version of the browser.[7]

Reverse Proxy

A reverse proxy is (usually) an Internet-facing proxy used as a front-end to control and protect access to a server on a private network, commonly also performing tasks such as load-balancing, authentication, decryption or caching. Websites could use reverse proxy to reroute traffic to avoid censorship.[8]

Virtual Private Networks (VPNs)

Using Virtual Private Networks, a user who experiences internet censorship can create a secure connection to a more permissive country, and browse the internet as if they were situated in that country. Some services are offered for a monthly fee, others are ad-supported.


A Sneakernet is the transfer of electronic information, especially computer files, by physically carrying data on storage media from one place to another. A sneakernet can move data regardless of network restrictions simply by not using the network at all.[9]



CGI proxies use a script running on a web server to perform the proxying function. A CGI proxy client sends the requested url embedded within the data portion of an HTTP request to the CGI proxy server. The CGI proxy server pulls the ultimate destination information from the data embedded in the HTTP request, sends out its own HTTP request to the ultimate destination, and then returns the result to the proxy client. A CGI proxy tool's security can be trusted as far as the operator of the proxy server can be trusted. CGI proxy tools require no manual configuration of the browser or client software installation, but they do require that the user use an alternative, potentially confusing browser interface within the existing browser.

HTTP proxies send HTTP requests through an intermediate proxying server. A client connecting through an HTTP proxy sends exactly the same HTTP request to the proxy as it would send to the destination server unproxied. The HTTP proxy parses the HTTP request; sends its own HTTP request to the ultimate destination server; and then returns the response back to the proxy client. An HTTP proxy tool's security can be trusted as far as the operator of the proxy server can be trusted. HTTP proxy tools require either manual configuration of the browser or client side software that can configure the browser for the user. Once configured, an HTTP proxy tool allows the user transparently to use his normal browser interface.

Application proxies are similar to HTTP proxies, but support a wider range of online applications.

Peer-to-peer systems store content across a range of participating volunteer servers combined with technical techniques such as re-routing to reduce the amount of trust placed on volunteer servers or on social networks to establish trust relationships between server and client users. Peer-to-peer system can be trusted as far as the operators of the various servers can be trusted or to the extent that the architecture of the peer-to-peer system limits the amount of information available to any single server and the server operators can be trusted not to cooperate to combine the information they hold.

Re-routing systems send requests and responses through a series of proxying servers, encrypting the data again at each proxy, so that a given proxy knows at most either where the data came from or is going to, but not both. This decreases the amount of trust required of the individual proxy hosts.

Web site
alkasir[10] HTTP proxy Yemeni journalist Walid al-Saqaf free Uses 'split-tunneling' to only redirect to proxy servers when blocking is encountered. Is not a general circumvention solution and only allows access to certain blocked websites. In particular it does not allow access to blocked websites that contain pornography, nudity or similar adult content.
Anonymizer[11] HTTP proxy Anonymizer, Inc. paid Transparently tunnels traffic through Anonymizer.
CGIProxy[12] HTTP proxy James Marshall free Turn a computer into a personal, encrypted proxy server capable of retrieving and displaying web pages to users of the server. CGIProxy is the engine used by many other circumvention systems.
Flash proxy[13] HTTP proxy Stanford University free // Uses ephemeral browser-based proxy relays to connect to the Tor network.
Freegate[14] HTTP proxy Dynamic Internet Technology, Inc. free Uses a range of open proxies to access blocked web sites via DIT's DynaWeb anti-censorship network.
Freenet[15] peer-to-peer Ian Clarke free A decentralized, distributed data store using contributed bandwidth and storage space of member computers to provide strong anonymity protection.
(originally Invisible Internet Project)
re-routing I2P Project free Uses a pseudonymous overlay network to allow anonymous web browsing, chatting, file transfers, amongst other features.
Java Anon Proxy[17] (also known as JAP or JonDonym) re-routing (fixed) Jondos GmbH free or paid Uses the underlying anonymity service AN.ON to allow browsing with revocable pseudonymity. Originally developed as part of a project of the Technische Universität Dresden, the Universität Regensburg, and the Privacy Commissioner of Schleswig-Holstein.
Psiphon[18][19] CGI proxy Psiphon, Inc. free A simple-to-administer, open-source Internet censorship circumvention system in wide-scale use, with a cloud-based infrastructure serving millions.
Proxify[20] HTTP proxy UpsideOut, Inc. free or paid An encrypted, public, web-based circumvention system. Because the site is public, it is blocked in many countries and by most filtering applications.
StupidCensorship[21] HTTP proxy Peacefire free An encrypted, public, web-based circumvention system. Because the site is public, it is blocked in many countries and by most filtering applications. is a similar site based on the same software.
Tor[22] re-routing (randomized) The Tor Project free Allows users to bypass Internet censorship while providing strong anonymity.
Ultrasurf[23] HTTP proxy Ultrareach Internet Corporation free Anti-censorship product that allows users in countries with heavy internet censorship to protect their internet privacy and security.

SSH tunneling

By establishing an SSH tunnel, a user can forward all their traffic over an encrypted channel, so both outgoing requests for blocked sites and the response from those sites are hidden from the censors, for whom it appears as unreadable SSH traffic.

Shadow Internet and cell phone networks

In June 2011 the New York Times reported that the U.S. is engaged in a "global effort to deploy 'shadow' Internet and mobile phone systems that dissidents can use to undermine repressive governments that seek to silence them by censoring or shutting down telecommunications networks."[24]


According to GlobalWebIndex, over 400 million people use virtual private networks to circumvent censorship or for increased level of privacy.[3]

The Berkman Center for Internet & Society's 2007 Circumvention Landscape Report included the following observations:[25]

We were reassured to discover that most [circumvention] tools function as intended. They allow users to circumvent Internet censorship, even in countries like China and Vietnam, which use sophisticated technology to filter. However, we discovered that all tools slow down access to the Internet, that most tools featured serious security holes [some of which were patched during or shortly after the study], and that some tools were extremely difficult for a novice Internet user to use. ...we guess that the number of people using circumvention tools is around two to five million users worldwide. This number is quite high in absolute terms but quite low relative to the total number of filtered Internet users (China alone has over two hundred million Internet users). Even accepting likely high end estimates of the project developers, we believe that less than two percent of all filtered Internet users use circumvention tools. ... we now think it likely that simple web proxies represent at least as great if not greater proportion of circumvention tool usage as do the more sophisticated tools included in this report. An assumption of this report was that only users at the margins would rely on simple proxies because of the trouble of constantly finding new proxies as old ones were blocked by countries. We now have some evidence that that assumption is false (both that users are not using the simple proxies and that filtering countries are blocking simple proxies quickly). It’s worth nothing that none of the developers we spoke to, individually and at our convening, foresaw a “silver bullet” that would “solve” the problem of filtering circumvention. All the tools rely, to a certain degree, on providing more proxies than the authorities can block and continuing to create new proxies as old ones are blocked. The preferred technical term for this strategy is “Whack a Mole,” a reference to an American fairground game, and while none of the developers are thrilled about an ongoing arms race with censors, some are taking complex steps to ensure they’ll have many more proxies than the government can shut down. We are confident that the tool developers will for the most part keep ahead of the governments' blocking efforts.

See also


  1. ^ Freedom of connection, freedom of expression: the changing legal and regulatory ecology shaping the Internet, Dutton, William H.; Dopatka, Anna; Law, Ginette; Nash, Victoria, Division for Freedom of Expression, Democracy and Peace, United Nations Educational, Scientific and Cultural Organization (UNESCO), Paris, 2011, 103 pp., ISBN 978-92-3-104188-4
  2. ^ New Technologies Battle and Defeat Internet Censorship, Global Internet Freedom Consortium, 20 September 2007
  3. ^ a b Marcello Mari. How Facebook's Tor service could encourage a more open web. The Guardian. Friday 5 December 2014.
  4. ^ "Risks", Internet censorship wiki, accessed 2 September 2011
  5. ^ a b c d Everyone's Guide to By-passing Internet Censorship, The Citizen Lab, University of Toronto, September 2007
  6. ^ "Circumventing Network Filters Or Internet Censorship Using Simple Methods, VPNs, And Proxies", Not As Cool As It Seems, 16 December 2009, accessed 16 September 2011
  7. ^ Steven Millward (22 November 2009). "Opera accused of censorship, betrayal by Chinese users". CNet Asia. 
  8. ^ "faq of". 
  9. ^ Sullivan, Bob (13 April 2006) Military Thumb Drives Expose Larger Problem MSNBC Retrieved on 25 January 2007.
  10. ^ "About alkasir",, accessed 16 September 2011
  11. ^, Anonymizer, Inc., accessed 16 September 2011
  12. ^ CGIProxy", James Marshall, accessed 17 September 2011
  13. ^ "Flash proxies", Applied Crypto Group in the Computer Science Department at Stanford University, accessed 21 March 2013
  14. ^ "About D.I.T.", Dynamic Internet Technology, accessed 16 September 2011
  15. ^ "What is Freenet?", The Freenet Project, accessed 16 September 2011
  16. ^ "I2P Anonymous Network", I2P Project, accessed 16 September 2011
  17. ^ "Revocable Anonymity", Stefan Köpsell, Rolf Wendolsky, Hannes Federrath, in Proc. Emerging Trends in Information and Communication Security: International Conference, Günter Müller (Ed.), ETRICS 2006, Freiburg, Germany, 6–9 June 2006, LNCS 3995, Springer-Verlag, Heidelberg 2006, pp.206-220
  18. ^ "About Psiphon", Psiphon, Inc., 4 April 2011
  19. ^ "Psiphon Content Delivery Software", Launchpad, accessed 16 September 2011
  20. ^ "About Proxify", UpsideOut, Inc., accessed 17 September 2011
  21. ^ About, Peacefire, accessed 17 September 2011
  22. ^ "Tor: Overview", The Tor Project, Inc., accessed 16 September 2011
  23. ^ "About UltraReach", Ultrareach Internet Corp., accessed 16 September 2011
  24. ^ "U.S. Underwrites Internet Detour Around Censors", James Glanz and John Markoff, New York Times, 12 June 2011
  25. ^ 2007 Circumvention Landscape Report: Methods, Uses, and Tools, Hal Roberts, Ethan Zuckerman, and John Palfrey, Beckman Center for Internet & Society at Harvard University, March 2009

External links

  • Casting A Wider Net: Lessons Learned in Delivering BBC Content on the Censored Internet, Ronald Deibert, Canada Centre for Global Security Studies and Citizen Lab, Munk School of Global Affairs, University of Toronto, 11 October 2011
  • Censorship Wikia, an anti-censorship site that catalogs past and present censored works, using verifiable sources, and a forum to discuss organizing against and circumventing censorship
  • "Circumvention Tool Evaluation: 2011", Hal Roberts, Ethan Zuckerman, and John Palfrey, Berkman Centre for Internet & Society, 18 August 2011
  • "Circumvention Tool Usage Report: 2010", Hal Roberts, Ethan Zuckerman, Jillian York, Robert Faris, and John Palfrey, Berkman Centre for Internet & Society, 14 October 2010
  • Digital Security and Privacy for Human Rights Defenders, by Dmitri Vitaliev, Published by Front Line - The International Foundation for the Protection of Human Rights Defenders
  • "Digital Tools to Curb Snooping", New York Times, 17 July 2013
  • "DNS Nameserver Swapping", Methods and Scripts useful for evading censorship through DNS filtering
  • How to Bypass Internet Censorship, also known by the titles: Bypassing Internet Censorship or Circumvention Tools, a FLOSS Manual, 10 March 2011, 240 pp. Translations have been published in Arabic, Burmese, Chinese, Farsi, Russian, Spanish, and Vietnamese
  • Internet censorship wiki, provides information about different methods of access filtering and ways to bypass them
  • "Leaping over the Firewall: A Review of Censorship Circumvention Tools", by Cormac Callanan (Ireland), Hein Dries-Ziekenheiner (Netherlands), Alberto Escudero-Pascual (Sweden), and Robert Guerra (Canada), Freedom House, April 2011
  • "Media Freedom Internet Cookbook" by the OSCE Representative on Freedom of the Media, Vienna, 2004
  • "Online Survival Kit", We Fight Censorship project of Reporters Without Borders
  • "Selected Papers in Anonymity", Free Haven Project, accessed 16 September 2011
  • "Ten Things to Look for in a Circumvention Tool", Roger Dingledine, The Tor Project, September 2010
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