Within a single country mandate, different ISPs implement censorship with different filtering tools and mechanisms: Thailand's AS 9737 and AS 17552 use structurally distinct block-page templates (vector 17 is ~1,000 bytes using div layout; vector 8 is ~6,000 bytes using table layout). Both ISPs actively obfuscate their filtering product by reporting generic 'Server: Apache/2.2.9 (Debian)' or 'Server: Apache' HTTP headers instead of the actual product identifier.

Page length comparison at a 30.19% size-difference threshold achieves a 95.03% true positive rate and 1.371% false positive rate for block page detection, outperforming DOM similarity (95.35% TP, 3.732% FP) on false positive rate and cosine similarity (97.94% TP, 1.938% FP, 74.23% precision) on precision. These metrics were evaluated via ten-fold cross-validation on the ONI dataset of ~500,000 entries from 49 countries spanning 2007–2012.

§4.2, Table 1 evaluation

Five commercial filtering products (FortiGuard, Squid, Netsweeper, Websense, WireFilter) were identified in 7 of 36 block-page clusters via copyright notices in HTML comments, HTTP header strings, or URL path patterns; the remaining 29 clusters contained no identifying markup. WireFilter was first detected in the wild in Saudi Arabia (AS 25019) in 2011, representing a newly deployed filtering product not previously observed in measurements.

§5.2, Table 2 detection

Applying automated block-page detection to the ONI dataset (49 countries, 2007–2012) reveals that Burma's (AS 18399) censorship mechanism shifted from DNS redirection to a transparent proxy returning a custom block page in mid-2009, then block pages largely disappeared after Burma's late-2011 political liberalization. Saudi Arabia (AS 25019) shows a similar transition with WireFilter replacing an unidentified prior tool in 2011, with two concurrent block-page templates suggesting multiple simultaneous filtering devices.

§6 evaluation

Term frequency clustering of block pages achieves an F-1 measure of 0.98, correctly recovering manually identified block-page templates; page-length clustering performs far worse at F-1 of 0.64. Across the full ONI dataset, only 37 distinct term frequency vectors were found from five years of measurements, indicating that filtering vendors rarely change block-page HTML structure.

§5.1, §5.2 evaluation

The largest single source of censored domains in the GNL is MESA lab's SNI monitoring dataset (E21-SNI-Top200w.txt) containing 57,362 censored domains, and E21-SNI-Top120W-20221020.txt with 36,467 domains—totaling over 93K domains from network tap data alone for a single country (E21 = Ethiopia per InterSecLab attribution). A separate Xinjiang dataset (XJ-CUCC-SNI-Top200w.txt) contains 13,604 domains. These datasets "do not seem to come from popular domain lists, and instead appear to be gathered from network taps," confirming that Geedge builds censorship target lists directly from passive traffic observation.

2026-sheffey-geedge §4.2, Table 3 dpisni-blockingmeasurement-platform

Of 6,915,266 domains extracted from the 572 GiB Geedge Networks Leak (GNL), 298,955 censored domains (93.7% of all GNL-censored domains) appear in neither Tranco top-1M nor CitizenLab test lists. Measurements across China (Guangzhou/Nanjing), Myanmar, Pakistan, and Algeria confirmed censorship via DNS injection and SNI-based TLS connection termination. The GNL covers 25–62% of Tranco-censored domains across countries, showing substantial but incomplete overlap. This vendor-side ground truth reveals a censorship surface roughly two orders of magnitude larger than curated academic test lists.

2026-sheffey-geedge §4.1, Table 2 dpisni-blockingdns-poisoningmeasurement-platform

Russian TSPU devices directly block ECH by dropping ClientHello messages that contain both an ECH extension and the outer SNI hostname "cloudflare-ech.com" — the static outer SNI Cloudflare advertises in all its ECH configurations. Blocking affects both TLS and QUIC. ECH connections to servers with Cloudflare ECH support but outside Cloudflare's official IP ranges are NOT blocked. TCP segmentation alone or TLS record fragmentation alone did NOT bypass TSPU ECH blocking, but combining both techniques did circumvent it. TSPU has also added TCP reassembly capabilities that defeat previously effective fragmentation-only bypasses.

2025-niere-encrypted §5, Figure 5 dpirst-injectionmiddlebox-interference

The GFI's HTTP and HTTPS filters are now stateful (requiring initial SYN packet with matching sequence numbers) and have been activated on all TCP ports—not only standard ports 80 and 443 as reported by prior studies. This is a significant departure from previous work that found stateless HTTP/HTTPS blocking limited to standard ports. The HTTP filter injects a 403 Forbidden blockpage (not RST packets as used by the GFW), while HTTPS injects a single RST+ACK packet. The GFI also exhibits TCP non-compliance (not requiring a full three-way handshake to trigger filtering), enabling outside-in measurement without in-country servers.

2025-tai-irblock §2.1, §3.2 dpirst-injectionpacket-injectionmiddlebox-interference

Wrana et al. systematically assess how well existing surveillance and censorship mechanisms can target users of Future Internet Architectures (FIAs) — including NDN, SCION, XIA, and MobilityFirst — finding that DPI and flow-correlation techniques from the current internet map onto FIA traffic with moderate adaptation. The paper identifies that FIA naming/addressing schemes introduce new censorship attack surfaces (e.g., content-name-based filtering in NDN) not present in IP-based architectures.

2025-wrana-sok-surveillance §4, §5 dpiflow-correlationmeasurement-platform

The Henan Firewall is stateless in two exploitable ways: (1) it requires the TCP header to be exactly 20 bytes—enabling any TCP option (e.g., TCP Timestamps, which Windows disables by default) to bypass it entirely; (2) it does not perform TCP reassembly, so splitting a TLS ClientHello across two TCP segments such that the SNI extension straddles the boundary bypasses the censor. Both bypasses require only client-side changes and have already been implemented in Xray, GoodbyeDPI, and Shadowrocket. TLS record fragmentation (splitting the ClientHello across multiple TLS records within one TCP segment) also defeats both the Henan Firewall and the GFW, since neither performs TLS reassembly.

2025-wu-regional-censorship §4.3 / §6 sni-blockingdpimiddlebox-interference