What is China’s Great Firewall?
How the world's largest censorship apparatus works — and how to circumvent it
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The Great Wall of China, one of the great wonders of the ancient world, was erected to protect the kingdom from invading armies. Today, another wall exists, no less tangible even if unseen. China’s Great Firewall is the largest and most sophisticated censorship system in the world. Controlling both content traffic at the service level and infrastructure, it separates the Chinese internet from the rest of the world, limiting Chinese people's free access to information and free expression.
In fact, the internet in China should be understood more as a national intranet, which is heavily regulated and isolated from the rest, than as a global internet. And this, of course, is no accident: it is ideologically and politically motivated.
“Anti-China forces in the West have constantly and unsuccessfully attempted to exploit the internet to ‘overthrow China’... Our ability to maintain our position and win this battle on the internet has a direct influence on the ideological and political security of our country.”
– Xi Jinping, speech at the National Propaganda and Ideology Conference, August 2013
Thus, the maintenance, expansion, and modification of China’s Great Firewall is an active state policy, varying according to state interests.
How the Great Firewall works
この規模の監視・検閲システムがどのように機能するかを理解するために、インターネットのグローバルなアーキテクチャとインフラについて簡単に振り返ってみましょう。
インターネットサービスプロバイダ (ISP) は、個人や組織のローカルネットワークをインターネットに接続する役割を担っています。 ISPs basically operate as gateways to other parts of the global network, managing the hardware necessary to establish and maintain these connections.
Unlike most of the world, ISPs in China are not private companies, but entities directly linked to the government, in particular China Unicom and China Telecom. Both constitute the backbone of the Chinese internet, that is, the main infrastructure that manages everything from national data traffic — through network cables, servers, and routers — to international traffic, through gateways and intercontinental submarine cables.
Using techniques such as IP filtering, DNS domain blocking, and deep packet inspection (DPI), these companies are able to detect and block content deemed sensitive or undesirable by the Chinese government, both within China and on international connections. This means that when Chinese people try to access foreign websites or communicate with people outside China, their data must pass through these control points where it is monitored, analyzed, and, if necessary, blocked or limited by the Great Firewall.
Therefore, censorship occurs at multiple layers: ISPs, data centers, and national traffic exchanges. It ranges from content filtering, throttling, service blocking, and even complete internet suspension. All of this is implemented uniformly by state-owned companies under centralized government control.
Finally, it is worth noting that the greatest regulation occurs at the international exchange points of the Chinese internet backbone (Beijing, Guangzhou, Shanghai, Urumqi, Xi'an). However, the Great Firewall operates nationally.
Notable cases of China’s Great Firewall censorship
Shaoguan incident (2009)
Following interethnic conflicts in Shaoguan, Guangdong province, the Chinese government completely cut off internet access in the Xinjiang autonomous region, directly affecting 20 million people, mostly of Uyghur ethnicity – an Islamic ethnic minority of China. The internet shutdown was used as a means to control information, prevent external communication, and contain protests and complaints. [1]
CryptoCurrency Ban (2017–2021)
In 2017, at the height of the global cryptocurrency boom, Chinese authorities blocked access to major cryptocurrency exchanges. In 2021, regulation became stricter, ultimately leading to cryptocurrency transactions being made illegal in China. [2]
Increased censorship in 2023 during Xi Jinping's election
According to a report presented at the 2023 USENIX Security Symposium, there was a significant increase in censorship of encrypted traffic in the months leading up to Xi Jinping's re-election. Strict techniques, including advanced statistical analysis and specific heuristics, were widely used to detect and block encrypted connections.
However, shortly after the election, there was a notable reduction in this intensified censorship, indicating that the Great Firewall's control responds directly to the specific political contexts of the Chinese government. [3]
Winnie the Pooh Censorship (2017–Present)
Beginning in mid-2017, images and references to Disney’s Winnie the Pooh were systematically removed from Chinese social media and streaming platforms after netizens memes began comparing the bear to President Xi Jinping. [4]
Censorship circumvention and resistance
Embedding privacy into technology, through the implementation of techniques that confuse censors, is the fastest way to circumvent and resist a mega-censorship infrastructure like China’s Great Firewall.
AmneziaWG
実用的な例として、**NymVPN**で採用されているWireGuardのフォークであるAmneziaWGプロトコルが挙げられます。これは、WireGuardの従来の動作を変更し、ディープパケットインスペクション（DPI）に対抗するように設計されています。 Among its strategies are sending fake packets before the handshake and varying headers between packets — tactics that make automatic detection by rigid DPI patterns difficult, without compromising connection efficiency.
Tor
The Tor project offers robust alternatives to circumvent censorship in China. These include:
- WebTunnel disguises traffic as regular HTTPS access
- Snowflake uses ephemeral proxies to create connections that are difficult to track
- Private obfs4 bridges avoid detection by not being publicly listed
- Meek-azure camouflages traffic as if it were from large cloud services, albeit with bandwidth limitations.
These tools, as Tor notes, comprise an essential arsenal in the fight against digital censorship and demonstrate how reverse engineering and decentralization remain fundamental strategies for ensuring freedom and access to information.
NymVPN’s censorship resistance project
In 2025, Nym is strengthening NymVPN's anti-censorship techniques. In addition to the already implemented AmneziaWG as the default protocol for its Fast mode, the censorship resistance team is currently working on:
- Hardening APIs and infrastructure (including more secure domain resolutions and more resilient configuration retrieval) for greater stability under restrictive networks
- Integrating evasion transports such as VMess/V2Ray, obfs4, and TLS tunnels (XRay/ShadowTLS style), as well as using “commoditized” QUIC, WebRTC, and TLS with obfuscation to blend in with ordinary traffic
- Post-quantum strengthening, updating the mixnet packet format and adding post-quantum handshake to an improved obfs4.
For more information on censorship resistance within the Nym community, check out Nym’s official roadmap.
Conclusion
インターネット監視は、市場として、また人口管理の一形態として、政治的なスペクトル全体にまたがっています。 Much less than a partisan position, the core of so-called surveillance capitalism – or would it be better in China to call it surveillance communism? – is the understanding of behaviors, tastes, and preferences with the ultimate intention of “conducting behaviour” – i.e., producing new trends in accordance with the interests of the surveillance agent.
This population control and surveillance of individuals – based on knowing where an individual is, what they do, who they communicate with, what they access online – is only possible due to a centralized infrastructure that does not prioritize user privacy.
China's Great Firewall and its success in building the world's largest censorship system are a direct legacy of an internet that was born as an American weapon during the Cold War, exposed information about users and the networks that constitute it, and was quickly privatised with the commercial power of the internet in mind.
Surveillance has thus become a global and connected market, in which countries and companies around the world collaborate to control populations. This was the case with China's Great Firewall, which in its early years had the collaboration of American big tech companies to get off the ground, and today exports censorship and surveillance technology to various countries.
The question, however, of how to oppose this industry is not a simple one. How can we resist surveillance when we are surrounded by such a politically and financially profitable business?
繰り返しになりますが、私たちは、匿名化技術の組み込みを技術に直接取り入れること、および「信頼」をパラメータとして依存しないアーキテクチャの実装を支持いたします。
But beyond that, we might ask: what if we manage to make the free internet something as interesting as — or even more interesting than — the monitored internet?
Indeed, that is the whole appeal of Web3.
Nym's Noise Generating Mixnet
The Great Firewall of China: FAQs
The Great Firewall combines DNS filtering, IP blocking, and deep packet inspection to restrict access to foreign sites. It identifies and blocks VPN traffic patterns, making most traditional VPNs detectable and ineffective inside China.
VPN use is heavily restricted. Only government-approved VPNs are technically legal, but they lack privacy protections and are often monitored by the government. Tools like NymVPN use decentralized routing and advanced censorship resistance technology, making detection and blocking more difficult.
Yes. Decentralized VPNs like NymVPN don’t rely on centralized servers or fixed IP addresses, so they’re harder for censorship systems to detect or block. This architecture allows access to censored content without exposing user data.
China’s censorship model has influenced similar systems in other countries. Understanding how it works helps developers and privacy advocates strengthen global resistance to surveillance and information control.
About the authors
Pedro Sydenstricker
Community WriterCasey Ford. PhD
Technical reviewer