The paper proposes using CAPTCHAs (hard AI problems) to gate forwarder-list access, forcing the blocker to expend human resources solving every puzzle while each blockee solves only one. However, a 'stealing cycles from humans' attack allows a censor to relay CAPTCHAs to unwitting third parties (e.g., visitors to an attacker-operated website) who solve them on the censor's behalf.

The paper presents a systematic taxonomy of blocking criteria across ISO/OSI layers: circumstance-based (addresses including sender/receiver/kind/physical location; timing including send time, receive time, duration, frequency; data-transfer properties; services including protocols, names, addresses) and content-based (file type/MIME, statistical detection of encrypted or compressed data, pattern matching for keywords or phrases, and website fingerprinting via request-count/byte-volume signatures).

§4, Appendix A defense

NAT and firewalls make volunteer forwarders (JAPR) unreachable for inbound connections by default, removing the incentive for volunteers to reconfigure their systems for no personal benefit. The design response is to reverse the connection direction — JAPR initiates contact with JAPB — shifting the NAT/firewall configuration burden to the motivated blockee who gains direct benefit from solving it.

§6.4 deployment

For a secure steganographic system the embedding ratio is at least 1:10, meaning 1 MB of web content requires 10 MB of transmitted cover data; for a system robust against active attacks (e.g., StirMark bilinear distortions) the ratio is probably 1:100. A censor need not break the steganographic algorithm with high accuracy — suspicion alone is sufficient, since the censor can probe suspected nodes directly by acting as a blockee.

§5.1 evaluation

The protocol between blockee and volunteer forwarder is designed to be transport-layer independent from the outset, allowing substitution of plain TCP with SSL tunnels, SMTP, or steganographic channels as the censor escalates detection. The system is intentionally deployed in a weak initial form to observe how quickly and in what manner the censor adapts, then hardened iteratively based on measured censor behavior.

§6.2 defense

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