MassBrowser proxies operate on NATed IP addresses shared with other users and services, meaning blocking them imposes collateral damage on unrelated parties. The proxy IP pool scales linearly with user count via client-to-client proxying, and IPs rotate as volunteers move between networks, making enumeration-and-block strategies progressively more costly for censors.

Survey data indicates 31% of Chinese Internet users use VPN services compared to Tor's approximately 2 million daily users globally, and centralized non-anonymous systems like Lantern and Psiphon dominate adoption over anonymity-focused tools. The paper argues this demonstrates that the majority of censored users prioritize blocking resistance over anonymity, supporting a separation-of-properties design principle.

§III-B policy

The majority of censored websites are blocked in only one or two countries, with political and news content showing the strongest geographic specificity. Figure 3 shows that of domains blocked in China, Iran, and Turkey, only 29 are blocked in both China and Turkey, while 27,852 are China-only and 1,564 are Iran-only, demonstrating that cross-region client-to-client proxying is broadly applicable.

§III-C, Figure 3 evaluation

In a traffic sample from a major non-anonymous circumvention tool (3.56 TB total, Feb 21, 2008), 48% of all proxied traffic belonged to websites that were not censored in Iran. Integrating CacheBrowsing to fetch CDN-hosted censored content directly further saves 41% of Buddy bandwidth for Alexa top-1000 websites.

§IV-B, §V-C evaluation

MassBrowser estimates operational cost at $0.0001 per active client per month at large scale; the domain-fronted Operator alone costs ~$0.001 per active client per month because signaling traffic volume is small. Domain fronting used for bulk data proxying is characterized as prohibitively expensive and not viable at scale.

§III-E, §VI-C evaluation

InterSecLab's 76-page analysis of the Geedge/MESA leak (based on nine months of indexing and translating >100,000 documents) characterizes the Tiangou Secure Gateway (TSG) product line as a commercially deployable detection stack that combines deep packet inspection, real-time mobile subscriber monitoring, active probing, ML-based traffic classifiers, and granular per-region rule sets. TSG is not a research prototype — leaked documentation includes deployment timelines and client government interactions for Kazakhstan, Ethiopia, Pakistan, Myanmar, and one unnamed country, with censorship rules explicitly tailored to each region.

2025-interseclab-internet-coup §3–§5 (InterSecLab report) dpiactive-probingml-classifiersni-blockingip-blockingtraffic-shapefully-encrypted-detect

Justice for Myanmar documents that Geedge Networks supplied Myanmar's military junta with GFW-derived surveillance and censorship infrastructure under Belt and Road frameworks following the February 2021 coup. The deployed system (Tiangou Secure Gateway / TSG) incorporates the same DPI, active-probing, and ML-classifier capabilities as the domestic Chinese GFW, giving Myanmar one of the most technically capable censorship systems in Southeast Asia.

2025-jfm-silk-road-surveillance §3, §5 dpisni-blockingip-blockingtraffic-shapeml-classifieractive-probing

Snowflake's sustained operation in heavily censored regions demonstrates that WebRTC must remain accessible to users, which in turn requires that TURN servers remain unblocked to support NAT traversal for peer-to-peer WebRTC connections. This transitive unblockability makes TURN service providers viable rendezvous channels for the Bridge Distribution Problem.

2025-vilalonga-extended §3.2 Bridge Distribution Problem ip-blockingactive-probing

TURN servers used by major applications such as Facebook Messenger for media relay are hypothesized to be less likely blocked in censored regions due to collateral damage to legitimate WebRTC traffic. Providers like Cloudflare, Metered Video, and ExpressTURN supply geographically distributed TURN infrastructure that can be used without any special configuration by a censorship evasion system.

2025-vilalonga-extended §1 Introduction & Background dpiactive-probingip-blocking

Traffic splitting across N TURN proxies (1 ≤ N ≤ M) is hypothesized to resist active probing because each TURN server responds to probing requests identically to a regular TURN server, providing no distinguishing signal. Additionally, proxy ephemerality combined with splitting allows on-the-fly migration to new proxies when existing ones are blocked, maintaining connectivity even under partial blocking.

2025-vilalonga-extended §3.3 Censorship Evasion active-probingip-blockingdpi

The paper defines Unauthenticated Push (UP) channels as a distinct archetype from signaling/rendezvous channels, characterized by three properties: strictly unidirectional delivery, no client authentication or account association required, and higher bandwidth (kilobytes to megabytes) to support software updates rather than just minimal proxy-address exchanges. This design deliberately shifts operational-security burden onto senders to approach receiver anonymity.

2025-vines-extended §1–§3 ip-blockingactive-probing