National Internet Censorship and Anti-Censorship Proxy Protocols

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National level cyberreview mechanism and the evolution of the countercensorship proxy agreement

Many people are still understanding the problem in the “trawling tool” language as if the success or failure of a client, a node, or a port were still connected. At the systemic level, what really works is identification, detection, coordinated blockade, resilience and cost control.The confrontation between the national network review and the counter-censorship proxy agreement has become a systemic engineering confrontation.

The confrontation no longer revolved around “the possibility that an agreement will be recognized”, but rather around “the appearance of an anomaly in the correspondence system”. What concerns us is how this judgement is formed.

This is not a "trawling tool history" but a system engineering confrontation.

First, let the boundary be clear: understanding this matter as an instrument of an iterative history would naturally underestimate the engineering difficulties of the vetting system and overestimate the decisiveness of the innovation of a single agreement.

In many non-technical narratives, stories are often told that there is a sort of proxy agreement, then the examiner identifies it, blocks it, then the community invents the next agreement, and so on. This is not entirely wrong, but it captures only the surface phenomenon. What actually happened was more like:

Counter-dimensional	What's the examiner's concern?	What is the anti-censor trying to solve?
Connection Create	Can suspicious connections be detected and interrupted at the earliest possible time	Can you make handshake look unusual?
Flow content	Whether protocol can be identified from specified features or encrypted exterior	Can you hide protocol fingerprints and metadata?
Interactive behaviour	Is it possible to identify the service provider through active detection?	Can you make unauthorized detection invisible for real services?
Network ecology	Availability of location nodes through address, domain name, certificate, infrastructure connection	Can you hide yourself with a larger ecology?
Cost structure	Affordability of large-scale identification and interdiction coverage	Can identification costs be pushed to a level where full implementation is difficult

It's not two software fights, but two systems competing who is better at dealing with uncertainty. The national review system is faced with mass flows, which cannot be as perfect as laboratories to understand everything, but must balance coverage, accident rates, real-time and cost. The protocol is not a static firewall, but a network governance machine that will observe, learn, reuse infrastructure capabilities.

There was much discussion about whether an agreement was dead, and it was therefore prone to distortion.Agreements are rarely imposed on a one-time technical nature, and more often they are gradually out of scale. For individuals, occasional use does not represent its continued validity at the system level; for reviewers, occasional omissions do not mean that the identification mechanism fails, and it has achieved governance objectives provided it significantly increases the cost of use, reduces stability and reduces dissemination efficiency.

What exactly is the National Network Review blocking?

To understand the subsequent evolution, we need to make clear the target function: what is to be blocked by a national web review is not just "access to a website" but also,The ability to move information across borders without permission and the infrastructure to build such mobility.

In terms of results, the review system usually does at least four things.

First, there is a direct disruption of content and destination. This means filtering specific domain names, IPs, keywords, resolution results or connected objects. This layer is most easily felt by ordinary users because it is a site that cannot be opened.

Secondly, it is the tunnel itself that is blocked. And instead of getting access to anything, the system will judge whether you are creating an unauthorized encrypted relay channel. The target identified here is not a web page, but a channel that is not a normal flow of business.

Thirdly, there is the disruption of the ability to resist circumvention. The review system is not content to block known nodes, but it will also target technical mechanisms that help users move continuously, rediscover nodes and reconnect. Many capabilities are important not “quick”, but “can they sustain resilience under sustained blow”.

Fourthly, there is deterrence and cost transfer at the governance level. The review does not always seek 100 per cent interception, and the more realistic goal is often to make circumvention unstable, expensive and unpredictable, ultimately giving up the majority ' s sustained attempts.From a governance perspective, it is quite different to make it easy for a small number of high-technology users to reach, and to stabilize it for large-scale ordinary users.

If the language is changed to engineering, the national review can be understood as a three-tier capability superseding:

Basic filter: general blockages such as IP, domain name, DNS, keywords, connection reset.
Agreement identification: Identification of suspicious tunnels based on handshake characteristics, explicit metadata, TLS fingerprints, distribution of package lengths, time series patterns, etc.
Behavioural confirmation: Identification of whether the target is a circumvention system through active detection, re-laying, correlation analysis, infrastructure graphics, abnormal flow detection, etc.

These three layers are either one or the other, but they are being added over time. The first two tiers are addressed by wide coverage, while the second is resolved by high faith confirmation. It is because of this layer that the anti-censorship technique will evolve from the beginning of encryption of content to the point where it will become a mere form of hiding in normal ecology, and then further, even if it is seen, it will be difficult to make a confirmation easily.

Phase 1: Base block and game of visible tunnels

The first phase of the assessment was that:When the vetting capacity also relies primarily on basic filtering and visual features, the most important function of the resistance programme is to load the original bare-faced requests for access into a encrypted tunnel.

Early interdiction techniques are not mysterious and often are used in the most visible positions.

The first position is DNS. Users usually interpret a domain name to IP before accessing it. DNS have been relying mainly on explicit UDP queries for a long time, giving access to by-visiting and answering: censorship does not necessarily require real control over authoritative DNS servers, and whenever you see a sensitive domain name query on the chain, you can pre-empt a solver response, and the client gets the wrong address, the contaminated cache. The result that users see at this point is simply “site unopenable”, but the bottom point of failure occurs before accessing the target site.

The second position is IP and route. That is, using a credible DNS to get the real IP, the connection still has to go through the operator and the international channel exit. The review system can blacklist some of the target addresses, discard the traffic on the border equipment or direct the package to the target prefix to an address that cannot be accessed through route strategy. It doesn't need to understand the specific pages you visit, but if you can't get TCP handshakes done, the connection will be time out.

The third position is the explicit content and simple protocol characteristics. Early HTTP requests, keywords, fixed ports, traditional VPN handshakes have given the reviewers a very direct grip. These requests are characteristic enough to complete a fairly rough shield.

The response of the first generation of resistance review programmes was also straightforward: do not let real access requests run naked and wrap them into a secure tunnel to a remote server. Users are connected locally to proxy servers, which replace users with access to target sites; if the reviewer only looks at the local to remote segment, the original HTTP request and the real access content cannot be seen.

This is why the first generation of proxy techniques, which are widely used, mostly emphasizes forwarding and encryption rather than confusion and disguise. As a result, they did address a specific problem: the flow of traffic directly hit by DNS, keywords, explicit target paths, which turned into a tunnel where it was difficult to read content with censorship equipment.

DNS contamination is directed at the local interpretation of the target domain by the user, but the site is bypassed if the real target is deciphered and accessed at a remote end; the IP blacklist is directed at the direct link path of the user to the target site, but if the user is connected to the proxy portal locally, the exit site access to the target site is moved to the other side of the network.

But the boundaries of this phase are also clear.Encryption can only hide the content, not the fact that it is a proxy connection. Once the agreement shakes hands, port habits, message formats, authentication, text sizes or connections have shown a stable feature, the tunnel becomes an identifiable object.

For example, in engineering, an agreement does not necessarily need to be declassified to be recognized. The review system can use “not the content but the mode” as a basis for identification, provided that it exposes fixed fields, predictable length, unusual time series or long-term binding of certain service-end behaviour at the start of the connection. Many of the underlying agency agreements are lost here: they hide the data, but they don't hide themselves.

The engineering inspiration left behind at this stage is not "encrypted" and, on the contrary:Encryption is a necessary condition, but never sufficient. The only way to secure the payload by encryption, rather than dealing with the protocol's appearance and connection, is to shift the confrontation from “look at the content” to “see the tunnel”.

If the typical characteristics of this phase are summarized, the following comparison is possible:

Characteristics	Early detection of tunnel programme advantages	Early detection of tunnel programme limitations
Content protection	Can hide access to content and top-level requests	Can't hide yourself as a proxy tunnel.
Complexity of deployment	Relatively simple, lower threshold	The features are stable and easily reusable identification rules
Interference resistance	We can bypass some direct content.	Weaknesses in the face of protocol recognition and bulk blockades
User Experience	Usually, it's available at low pressure.	Stability depends on the external environment and is not suitable for long-term public dissemination

That is why the confusion that followed is not enough to make the content readable.

Phase 2: from "encrypted transmission" to "flow confusion"

The main findings of the second phase are:When the review system begins to stabilize the identification of visible tunnels, the focus of the anti-censorship design shifts from hiding the content to concealing the identifiable features of the agreement itself.

The change here is that the examiner does not have to decrypt your proxy traffic, but can judge it not as normal traffic. The most direct way to do this is to watch the handshake. Many traditional tunnels have fixed-state machines at the beginning of the connection: some certification package is first issued, then some key consultation is entered, and a relatively stable package length and direction sequence appears. As long as the sequence is stable enough, it becomes a protocol fingerprint. Another type of approach is to look at statistical characteristics. Encrypted loads are close to random byte flows, which is good for the code, but may become signals in flow classification. The censorship system does not need to know what's in it, but it can put it in a suspicious pool, judging by "this is not like the usual Web handshake."

The response to the anti-censorship agreement is to reprocess the secret into less proxy-like secret. If a proxy agreement is identified because the handshake feature is too fixed, then a coat of clothing is added to it; if the package length and time sequence reveal that it does not resemble normal business flows, then try to disturb the statistical features observed externally; if the fixed port is easily cleaned, then move it to the more common carrying environment.

So the confusion became a phased keyword. The confusion here does not amount to indistinguishability in the strict sense, but rather to a less nuanced treatment of the project: by adding additional seals, random fillings, handshakes, long disturbances, disguises of the head, etc., the original nuanced proxy agreement is less nuanced.

The role of this phase is real. Many mapping studies and engineering experience have shown that the elimination of a few powerful features can significantly prolong the life of the agreement as long as the identification mechanism is more dependent on them. Especially when the review system needs to balance the costs of injury and error, the more common the flow and the less one-point-strong fingerprinting options are available, the less easy to be dealt with with in a single-size-fits-all manner.

But this phase also revealed a continuing problem:Confusion is not the same as disguised use.

Many so-called confusing agreements are more like saying that they do not make them look like they are, rather than making them look like a real business. These two are very different. The former is merely reducing the probability of being subjected to a rule-based mission, while the latter requires that the whole link be sufficiently consistent with host ecology in terms of handshakes, encryption layers, certificates, text structure, interactive rhythms, and failure behaviour.

The main result of the confusion phase is to render the simple matching ineffective; but it does not solve the more difficult problem:If the opponent is willing to observe the higher dimensions, you may still be seen as not being in normal traffic.

There is also a often neglected border at this stage: costs are rising on both sides. The challenge is to be able to upgrade the encryption to a continuous ability to maintain a changing set of external features, with the maintainer following the update to achieve, match the client and reduce the loss of performance; the reviewer is going to extend the rule from static field matching to a more detailed model analysis. Many agreements are not technically out of effect at short notice, but are gradually losing the engineering balance between the speed of renewal, compatibility and recognition pressure.

Historically, the legacy of this phase is not a specific confusion plugin, but rather an awareness:It is not enough to make yourself look like something else, and even harder to make yourself look like something else when you are detected, when you are counted for the long term, when you are connected to infrastructure. This has moved the confrontation to the next stage.

Phase III: Active detection, TLS disguise and protocol parasite

The main judgements of the third phase are:When passive identification is becoming less and less useful, the vetting system begins to proactively contact suspect targets, and the anti-censorship agreement must be upgraded from “reduced features” to “rejected recognition”.

This is a leap in the defensive relationship. In the first two phases, the reviewers were more concerned with observing traffic through the road, which was seen as not acting as a proxy; at this stage, many research and engineering observations pointed out that active detection was becoming a common capability. That is, when the system finds a certain address, port, domain name or handshake pattern suspicious, it does not draw conclusions on one observation alone, but interacts with it from an external simulation client to see if the other side will reveal the response characteristics of the agent service.

The idea of active detection can be understood as a knock-on test. If a service end is really a normal Web server, then a normal HTTP or TLS request should be received with a regular web page or standard TLS behaviour; if it is actually an agent, it is just waiting for some private handshake, then silence, abnormal disconnection, incorrect format return, or response to re-playing proxy handshakes may occur in the face of detection traffic. The system of review does not need to know at the outset what it is, and the possibility of excluding normal services through several rounds of testing increases the confidence of the embargo.

The review of the SNI is also an important example of this phase. TLS encrypts a lot of content, but the traditional SNI in TLS hands still explicitly exposes the domain name that the client wants to access. The review equipment was sensitive and allowed for the injection of a forged TCP RST into the two ends of the connection, allowing the parties to break off on their own initiative. When new agreements such as QUIC/HTTP3 arrive, the handshake structure has changed, but there are still observational and decomposition metadata in the initial package, and the reviewers will continue to look for new visible fields and deduceable signals.

This step has changed the very logic of many agreements. Because you're not just going to fool the catalogs on the road, but also a detector who knocks repeatedly, shakes hands again, tries different entries, judges your true identity on the basis of feedback.

So TLS disguises and protocols parasites start to look up.

The key to the TLS disguise is not to use TLS, it's to be safe.Embedding the proxy channel into the most common and one-strike-to-cut encryption carrier on the Internet. This includes making handshakes more like real HTTPS, making certificates, extensions, encryption packages, connecting behaviors closer to normal Web services, or at least less easily singled out on the TLS level.

Why can't this step be taken? Because a lot of modern Internet business runs on TLS. If a connection is clearly different from the dominant TLS ecology, it is naturally more visible; in turn, if it is close enough to the real Web server, the censorship system wants to carry it out without causing any harm, it will be much more expensive.

Here you can put a few types of design together. A trojan-like idea emphasizes “it looks like a normal HTTPS service”: a legitimate client enters the proxy semantic after TLS, while illegal detection sees as much as possible an ordinary Web response. The REALITY approach goes further by de-centres the ownership of certificates and domain names, but by borrowing the external features of the real site, making it more difficult for unauthorized observers to determine the identity of the service by simply relying on certificates and handshakes. The common denominator of these programmes is not “a field is magical”, but the question of identification is moved from “Is this port an agent” to “What is the difference between this connection and a normal TLS service”.

But TLS disguises themselves have borders.Like TLS and really TLS, it's not the same thing; handshakes look like Web traffic, and it's not the same thing as a whole session is like a real website. This has been repeatedly reminded by some papers and surveys: handshakes are made only on the surface, often without the ability to handle more detailed session-level analysis and proactive detection.

This leads to the idea of “agreement parasital”. The parasitic is not a simple shell but, to the extent possible, draws on the existing form of trust and flow in large-scale normal ecology to allow more external features to be shared between proxy flows and normal operations. The instinct behind it is clear:

If an agreement is entirely self-generated, it must bear the risk of being portrayed, modelled and specifically identified alone.
If an agreement is to borrow the mainstream infrastructure as much as possible, it can at least shift the identification problem from “identifying a small crowd agreement” to “stripping an anomaly from a large normal flow ecology”.

This is why many of the ideas that followed were no longer satisfied with "encrypted + confused" but rather emphasized the need to hide before authentication, not to respond to real detections, to decorate proxy services and ordinary business entry points, or to hide suspicious entry points after what appears to be completely normal Web services.

From the results of the project, it was not a magic field that was the most useful at this stage, but three principles:

Minimize exposure until authentication.
The detection is conducted as far as possible as a harmless or common service, rather than a semantic proxy endpoint.
And if you can use the big ecology, don't be alone.

But that does not mean that the problem is solved.When the review system begins to integrate TLS fingerprints, the context of the certificate, the time series of connections, infrastructure relations and the results of active detection, the benefits at the level of single agreements are significantly diminishing. The question is no longer just “Can this jump disguise the past” but “Is this set of entrances, this set of sessions, and whether this set of nodes can maintain a consistent and natural external image over the long term”.

Phase IV: From single-agreement confrontation to behavioural and ecological confrontation

The core judgements of phase IV are:When individual agreement fields and single handshakes are no longer sufficient to stabilize judgement, the focus of confrontation shifts to long-term behavioural and infrastructure relationships.

The object then observed is no longer a connection, but more like the life cycle of a service.

There are at least three technical routes that are becoming important here.

The first is behavioural level analysis. That is, instead of being attached to a certain powerful feature, it combines several weak signals: connection frequency, initial orientation, distribution of package lengths, free-time cycles, length of sessions, retransmission, day and night changes, customer group consistency, etc. Individual signals may not be sufficient to criminalize, but multiple superstitions may create an abnormal image of higher confidence. The counter-reviewer responded by making flow-orientation and time-series disturbances: instead of handshakes, the package, direction and spacing after the connection was established, should not be stabilized in the proxy model. The key to this is that the idea of the XTLS-Vision is discussed repeatedly: it is not just about what the "head of the agreement" looks like, but about the "the whole flow is not like a normal connection."

The second is eco-level analysis. In other words, it puts a node back in the infrastructure environment in which it is located: It is hanging in what AS section, whether it coexists with a regular website, whether the certificate and domain name have a natural evolutionary mark, whether there are batch quantitative deployment marks and whether it shares operational characteristics with other known suspicious nodes. This approach is particularly appropriate for those programmes that have been made similar to normal traffic at the level of single connections, as it circumvents the “show-the-sle-stream” constraint and turns to “the service cannot stand in the Internet ecology”. The response of the counter-censor is often no longer simply to switch agreements, but to spread out access, shorten the life cycle of nodes and bring the shell of the service closer to real Internet assets.

The third is hiding communications into mainstream volumes that are more difficult to violently block. The emphasis of Snowflake on borrowing WebRTC and temporary volunteer nodes is not how strong a node is, but rather how highly dispersed and dynamic the node is, making it difficult for the blockers to be covered permanently by static IP blacklists. More radical, covert thinking is trying to put data into high-frequency UDP interactions like video, voice, games, so that the outside looks like a normal real-time media stream. Their common purpose is to push the reviewer to a more awkward position: If only the agreement is read, it is like normal business; if it is cut off, it hurts real videoconferences, games or real-time communications.

This is why today many of the difficulties of circumvention are not at the level of the code, but at the more general engineering level:

How to avoid the continuous image of the portal after long exposure.
How to keep the service end maintained under normal business cases.
How to control side-to-side behaviour does not create overly consistent features.
How to trade off resilience, performance, deployment complexity and observable.

At this point, the marginal gains from single-agreement innovation will decline significantly. Not that the deal is not important, but that it is.It is difficult to design with one agreement, while simultaneously addressing exposure, proactive detection, behavioural modelling, ecological imagery and long-term operational risks. This is why more and more effective solutions have since been developed, which have moved away from understanding themselves as “a protocol” and more like a combination of “agreements + access controls + mainstream content + transport strategies + infrastructure options”.

At this point, the problem of resistance has become more like a complex problem of distributed systems, traffic engineering, credible access and confrontational testing, rather than a problem of passwords or network tunnels.

The main battlefield of the future is more like an anomaly in normal traffic.

The main battlefield will increasingly look like an anomaly rather than an agreed list management.

The reason is not great. As Internet traffic is increasingly defaulted on encryption, as mainstream protocols themselves evolve, and as proxy programmes become more and more proximate to normal ecology, it is difficult for reviewers to expect a small amount of visible features to stabilize all circumvention flows. Accordingly, it is more likely to rely on statistical learning, correlation analysis and multidimensional signal integration to identify “however it looks okay, but not too well combined” objects from a large pool of normal flows.

The change is not a slogan, but an observation unit: from a single bag, a single handshake, slowly becomes a session, node, user community and infrastructure relationship.

Put four stages together, probably this line:

Phase	What does the examiner see?	What does the main counter-censor say?	Emerging issues
Base block	Domain name, IP, explicit keyword, fixed target path	Putting real access to remote end and carrying it with local to remote encrypted tunnels	The tunnel itself is still visible.
Flow confusion	Handshake sequence, initial entropy, bag length and time sequence	Rewrite handshakes, add filling and length disturbances, and lower strong fingerprints	It doesn't have to be like real applications.
Active detection	Suspected ports, SNI, TLS fingerprints, service response	Unauthorized detection of general services, as close as possible to HTTPS/TLS ecology	Long-term sessions and infrastructure may still be abnormal
Behaviour and ecological confrontation	Session life cycle, nodal relationship, user group and infrastructure portrait	Flow consolidation, portal fragmentation, mainstream, temporary nodes and covert letters Dow	Complexity, performance depletion and increased injury constraints

If that judgement is true, then the constraints that will be faced by both sides in the future will be even more severe.

For the reviewer, the difficulty is that:

Normal flow volumes are large and fine particle size analysis is costly.
The cost of misadventure of real business flows is not always acceptable.
The evolution of agreements and the relocation of infrastructure will continuously change the baseline.
Overdependence on black box models can raise interpretative and maintenance issues.

The difficulty for the adversarial parties is that:

It is not enough to just imitate handshakes.
There is a need to control both the physical, service behaviour and ecological locations of connections.
The more the disguises are convoluted, the more the performance loss and deployment burden is usually brought on.
The greater reliance on macro-ecological parasites, the more subject to changes in host-ecosystem rules.

And that is why I am not convinced by the narrative “there will be a final agreement to solve the problem once and for all”. More realistically, both sides will keep rewriting the issue. The reviewers refer to the rules from the field level to the class of behaviour, then to the ecological level, while the circumventor confuses the strategy from the encryption to the disguise, parasitic and access control.Each victory is more of a local, temporary, conditional advantage than a final one.

Conclusion: There is no final victory, only a constant shift of battle.

If this historical clue must be tied, I would like to emphasize the following:There is no proxy agreement called the “final victory” and no permanent static and effective review mechanism.

The NRM is not a product, it is a continuously upgraded governance and engineering capability; the NSA is not a document format, but a set of absconding abilities that move, absorb host ecology and re-adapt external features.

So, what should be remembered is that there is never a lot of tool names, but rather an evolutionary chain: a review of the way from content blockage to tunnel identification, voluntary identification and long-term painting; circumvention from encryption to confusion, disguise, parasitic, and the overall design of access and operation.

In the long run, this game will not end, but will continue to shift the battlefield. The past was a struggle over explicit content and fixed agents, later over handshake features and flow appearances, then over active detection, behavioural modelling, ecological connections and the identification of anomalies in normal Internet traffic.The tools will be outdated, the agreement will be renamed and only the constraints, costs and borders will remain.