The Chinese GFW enumerated all Tor bridges within approximately one month by deploying censoring agents that impersonated regular users, demonstrating that CAPTCHA- and email-based proxy distribution mechanisms are ineffective against resourceful state-level censors who can create large numbers of accounts and use human-based CAPTCHA-solving platforms.

A proxy assignment algorithm derived from the Gale-Shapley college admissions game, using multi-feature utility functions across five client metrics (proxy utilization capped at T, new-proxy request rate, blocked-proxy usage, known-blocked count, client distance) achieves superior connected-client ratios and lower wait times compared to state-of-the-art rBridge in all tested ecosystem configurations (Static, Slow, Alive, Popular), without requiring knowledge of individual client types at assignment time.

§IV, §VII defense

Omnipresent censors who distribute censoring agents across diverse geographic locations obtain significantly more proxies than circumscribed censors confined to a single subnet, because location diversity improves their utility scores in proximity-weighted proxy assignment systems.

§VII-B detection

A game-theoretic optimal censorship strategy — in which coordinated agents maximize a joint utility combining proxy discovery and blocking impact (equation 3, parameterized by ω) — is significantly stronger than both aggressive (immediate block) and conservative (timed-delay) heuristic strategies evaluated in prior work including rBridge; changing ω (surveillance vs. blocking preference) further modulates the damage a censor can inflict on any given distribution profile.

§VII-C evaluation

In a static proxy pool (λ=0, no new proxies added), the fraction of connected censored clients decreases monotonically to near zero regardless of censorship strategy, even at low censoring-agent fractions (ρ=0.05) and against a non-strategic aggressive censor with a strict-balanced distributor profile.

§VII-A 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