China's GFW was able to enumerate all Tor bridges distributed via IP address or Gmail account in under a month, demonstrating that standard small-subset distribution strategies are insufficient against a state-level adversary controlling large numbers of accounts and Sybils.

In simulated event-driven (crisis) blocking where all corrupt users simultaneously block bridges on day 300, available bridges drop from ~500 to ~150 and thirsty users spike to 25%; maintaining 50 reserve bridges (~10% of deployed stock) halves the thirsty-user count, and 100 reserve bridges nearly eliminates thirstiness among users who had accumulated sufficient credits.

§4.3.2 evaluation

Knowing a user's bridge assignment narrows the adversary's anonymity set to the small group sharing that bridge, deanonymizing Tor users even when the bridge itself is not compromised; rBridge addresses this using 1-out-of-m Oblivious Transfer, Pedersen commitments, and non-interactive zero-knowledge proofs so the bridge distributor learns nothing about which bridges a user holds.

§5, §5.1 defense

rBridge tolerates up to ~30% malicious users with acceptable bridge protection, but fails at f≥50%; with f=5% under aggressive blocking, over 95% of users are never bridge-starved and ~50% of bridges are never blocked, while conservative blocking (corrupt users waiting 225 days before acting) causes ~10% of users to be thirsty 15% of the time because delayed blockers accumulate enough credits to inject additional malicious invitees.

§4.3.2 evaluation

rBridge outperforms Proximax by at least one order of magnitude across all robustness metrics under aggressive blocking with 5% malicious users: to support 200 users for 30 days, Proximax requires at least 2400 bridges while rBridge needs only 108, and in Proximax fewer than 5% of bridges produce more than 20 user-hours versus 99% in rBridge.

§4.3.3 evaluation

The June 2025 Iran shutdown—carried out during the Iran-Israel war beginning ~June 19—did not use BGP route withdrawals as in 2019. Instead, authorities applied service-level restrictions at the national border: DNS poisoning of foreign destinations, protocol whitelisting permitting only pre-approved domestic services, and DPI to block circumvention-tool traffic. Iran's international traffic fell roughly 90% while the country's BGP routes remained advertised, making the shutdown invisible to BGP-based monitoring systems. OONI measurement volume, which totalled 121,333 in June 2025, collapsed to under 200 submissions on June 19-20.

2025-iran-shutdown-measurement Executive Summary / §2 dpidns-poisoningport-blockingip-blocking

Article 19 documents that Iran's National Information Network (NIN / SHOMA) was designed with explicit reference to China's Great Firewall as a model, with institutional mirroring: Iran's Supreme Council of Cyberspace parallels China's Cyberspace Administration of China, and both governments share a "cyber sovereignty" doctrine used to justify domestic content controls and cross-border technology transfer. The report frames Iran's filtering infrastructure as deliberately architected to replicate GFW capabilities, not as an independently developed system.

2026-article19-tightening-the-net §2, §3 dpisni-blockingdns-poisoningip-blockingbgp-hijackthrottling

Article 19 documents that Iran combines technical filtering with formal coercion of major foreign platforms (including Telegram, Instagram, and WhatsApp) to comply with content removal orders under threat of full blocking. The report notes that Iran's 2022 Women Life Freedom protests accelerated platform blocking when foreign operators refused compliance, demonstrating that the censorship system operates in two modes: coerce-and-allow for compliant platforms, block for non-compliant ones. Domain fronting via these platforms is therefore subject to sudden revocation if political conditions change.

2026-article19-tightening-the-net §6 ip-blockingdns-poisoningthrottling

Brussee measures a systematic pattern of Chinese government websites actively blocking access from outside China (the "reverse Great Firewall"), publishing a CSV dataset of affected domains (available at zenodo.org/records/18172145). The paper frames this outbound geo-blocking as a cybersecurity-motivated practice — Chinese authorities classify foreign access to domestic government infrastructure as an attack surface — distinct from the inbound information control goal of the GFW.

2026-brussee-reverse-great-firewall §3, §5 ip-blockingasn-blackholing

Brussee develops a conceptual framework distinguishing two logics of government geo-blocking: (1) information control (blocking inbound foreign content from domestic users) and (2) data sovereignty / attack-surface reduction (blocking outbound access by foreign actors to domestic systems). Chinese government site blocking of external IPs is motivated primarily by the second logic, creating an asymmetric internet topology where CN citizens cannot reach the outside world, and outside actors cannot probe CN government infrastructure.

2026-brussee-reverse-great-firewall §2, §4 ip-blockingasn-blackholing

ShieldShare demonstrates that an Android application can route all hotspot-client traffic through a VPN tunnel without root access by using a SOCKS5/HTTP/HTTPS proxy layer between the hotspot and the VPN, with per-client traffic accounting and quota management. The system works because Android's native hotspot does not forward VPN routing tables to connected clients; ShieldShare interposes a proxy that handles this. Released as open-source.

2026-edorh-shieldshare §Abstract ip-blocking