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.
Different techniques and resources are used to bypass Internet censorship, including cached web pages, website 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. According to GlobalWebIndex, over 400 million people use virtual private networks to circumvent censorship or for increased level of privacy.
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.
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.
In many jurisdictions accessing blocked content is a serious crime, particularly content that is considered child pornography, a threat to national security, or an incitement of violence. Thus it is important to understand the circumvention technologies and the protections they do or do not provide and to use only tools that are appropriate in a particular context. Great care must be taken to install, configure, and use circumvention tools properly. Individuals associated with high-profile rights organizations, dissident, protest, or reform groups should take extra precautions to protect their online identities.
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.
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.
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.
Copies of web sites or pages may be available at mirror or archive sites such as www.archive.org and the alternate sites may not be blocked. InterPlanetary File System is a permanent, open-source, decentralized and resilient technology of storing and sharing files, e. g. used by activists during the 2017 block of popflock.com resource in Turkey.
Alternative domain names may not be open. For example, the following domain names all refer to the same web site: http://wikimedia.org, http://www.wikimedia.org, https://web.archive.org/web/20120224022641/http://text.wikimedia.org/, and https://web.archive.org/web/20120224030658/http://text.pmtpa.wikimedia.org/ .
Or alternative URLs may not be open. For example: www.open.com vs. www.open.com/, blocked.com, open.com/, www.open.com/index.htm, and www.open.com/index.html.
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: http://22.214.171.124 (dotted decimal), http://3494942722 (decimal), http://0320.0120.0230.02 (dotted octal), http://0xd0509802 (hexadecimal), and http://0xd0.0x50.0x98.0x2 (dotted hexadecimal).
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 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 https protocol is recommended since it is encrypted and harder to block. A list of web proxies is available from web sites such as http://www.proxy.org/[permanent dead link] or by searching for "free web proxy". Most modern web browsers have preferences or allow plug-ins to enable proxies.
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.
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.
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.
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.
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.
It is also possible to combine multiple methods to hybrid methods, e.g., a smart DNS proxy server is a hybrid method (employing alternative DNS servers and VPNs) often used to circumvent geo-blocking.
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.
|alkasir||HTTP proxy||Yemeni journalist Walid al-Saqaf||free||www.alkasir.com||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||HTTP proxy||Anonymizer, Inc.||paid||www.anonymizer.com/||Transparently tunnels traffic through Anonymizer.|
|CGIProxy||HTTP proxy||James Marshall||free||www.jmarshall.com/||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||HTTP proxy||Stanford University||free||crypto
||Uses ephemeral browser-based proxy relays to connect to the Tor network.|
|Freegate||HTTP proxy||Dynamic Internet Technology, Inc.||free||www.dit-inc.us||Uses a range of open proxies to access blocked web sites via DIT's DynaWeb anti-censorship network.|
|Freenet||peer-to-peer||Ian Clarke||free||freenetproject.org||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||geti2p.net||Uses a pseudonymous overlay network to allow anonymous web browsing, chatting, file transfers, amongst other features.|
|Java Anon Proxy (also known as JAP or JonDonym)||re-routing (fixed)||Jondos GmbH||free or paid||anonymous-proxy-servers.net||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||CGI proxy||Psiphon, Inc.||free||psiphon.ca||A simple-to-administer, open-source Internet censorship circumvention system in wide-scale use, with a cloud-based infrastructure serving millions.|
|Proxify||HTTP proxy||UpsideOut, Inc.||free or paid||proxify.com/||An encrypted, public, web-based circumvention system. Because the site is public, it is blocked in many countries and by most filtering applications.|
|StupidCensorship||HTTP proxy||Peacefire||free||stupidcensorship.com/||An encrypted, public, web-based circumvention system. Because the site is public, it is blocked in many countries and by most filtering applications. mousematrix.com is a similar site based on the same software.|
|Tor||re-routing (randomized)||The Tor Project||free||www.torproject.org||Allows users to bypass Internet censorship while providing strong anonymity.|
|Ultrasurf||HTTP proxy||Ultrareach Internet Corporation||free||www.ultrasurf.us/||Anti-censorship product that allows users in countries with heavy internet censorship to protect their internet privacy and security.|
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."