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.

The paper enumerates five adversarial attack surfaces against a video-steganography UP channel: (1) wholesale blocking of the hosting platform, (2) mass-scanning and blocking encoded videos (noted as generally cost-prohibitive per the steganography literature), (3) enumerating videos via pseudorandom tags (feasible but hampered by tag-list overlap with unrelated content and time-window dynamics), (4) banning accounts posting encoded videos, and (5) tracking anticensorship users viewing encoded content. The pseudorandom tag window design specifically prevents preemptive enumeration because the top-n results for a tag at epoch t differ from those at t±1.

§2.1 detection

UP channels based on free third-party content hosting (video, audio, images, ML models) provide no-cost scalability: steganographic videos once uploaded are free to distribute to arbitrarily many users, and the channel sustains adversarial financial denial-of-service attacks without incurring operator costs. This contrasts with meek, SQS, AMPCache, and Skyhook, which face financial DoS risk because adversaries can drive up hosting costs by using those channels as intended.

§4 evaluation

Among surveyed channels, Skyhook, PushRSS, SQS, AMPCache, and Meek satisfy all three UP channel properties (unidirectional, no client auth, higher bandwidth); CloudTransport and Raven do not because they require authenticated user accounts; Tor's email- and Telegram-based bridge distribution also fails the no-auth requirement. The analysis was prompted in part by the 2022 GFW entropy-based blocking event, which required software updates to be pushed to users before fully-encrypted protocols could resume functioning.

§3 defense

A concrete UP channel implementation uses keyed steganographic encoding embedded in videos posted to a public hosting service (e.g., flickr.com), addressed via a time-epoch pseudorandom tag generator drawn from publicly known trending-topic lists. Clients query the top-n videos matching the current epoch tag and attempt decryption; real-world video size variability supports data transmissions from a few kilobytes (configuration updates) to megabytes (software updates).

§2 defense

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

Separating the Broker role (a server that holds and manages bridge information) from both the rendezvous channel and the censorship evasion system enables modular protocol design: the rendezvous carrier can be swapped independently of the proxy system. The authors identify broker authentication and multi-broker load distribution as open problems not addressed in the current prototype.

2024-vilalonga-looking §3.1, §5 active-probingip-blocking