During a two-month run in 2011 that coincided with the Jasmine Revolution protests, China's HTTP GET request backbone blacklist showed no additions or removals of keywords on a daily, weekly, or even monthly basis. Numerous current-event terms that triggered search engine censorship produced zero GET request RST responses, indicating the two censorship mechanisms operate on entirely different update timescales.

A maximum entropy named entity extraction (NEE) model trained on Chinese-language Wikipedia achieved 89.63% recall and 83.44% specificity for person names, 96.3% recall and 69.80% specificity for place names, and 87.56% recall and 88.40% specificity for organization names. Despite 0.42% precision for person names, the system reduces the number of words requiring censorship probes by nearly an order of magnitude while retaining nearly 90% of actual named entities.

§4.1 evaluation

To measure Chinese search engine censorship independently of backbone GET request filtering, the authors split each search engine HTTP GET request across multiple TCP packets so the server would reassemble the full query but routers performing single-packet keyword inspection would not see a complete match. This technique allowed ground-truth measurement of search engine responses free of backbone RST injection interference.

§3 defense

A controlled probe of two Chinese search engines found that the query 'fuck' triggered a legal notice that results had been removed, while 'fuck you' did not, suggesting that search engine censorship suppresses websites where a sensitive term appears prominently rather than matching exact byte strings in the query itself. The paper concludes this mechanism is topical and website-removal-based, not a static keyword blacklist.

§4.2 detection

During the 2011 Jasmine Revolution, words such as 'Jasmine Flower,' terms linked to Liu Xiaobo's Nobel Prize, and numeric references to presidential rent criticism triggered Chinese search engine censorship (results-removed warnings) but produced no HTTP GET request RST injections. This demonstrates that search engine filtering and backbone keyword filtering are independently operated layers that diverge sharply for rapidly evolving current-event content.

§4.2 detection

TLS connections to blocked services (instagram.com, telegram.org) were terminated by TCP RST immediately after the client's ClientHello, before any certificate exchange, confirming SNI-based DPI that reads the plaintext SNI extension and aborts the handshake. HTTP filtering additionally matched Host headers and URL keywords case-sensitively, with injected HTTP 403 pages or TCP RST responses, and case-change evasions were sometimes effective.

2025-aryapour-stealth-blackout §4.2, §4.3 sni-blockingdpirst-injectionkeyword-filtering

Iran's HTTP censor exhibits several parsing inconsistencies exploitable for evasion: (1) it is case-sensitive and ignores lowercase method variant "gET"; (2) it does not censor the Host header for HTTP version strings "HTTP", "1.1", and "example" (suggests a version regex of HTTP/.*); (3) when the Host header is absent, the path is not censored for versions "HTTP" and "HTTP/1"; (4) the body is never analyzed regardless of version. All HTTP and DNS censorship occurs at the same last-hop border node, suggesting centralized architecture.

2025-lange-i-ra-nconsistencies §3.2, Table 1 dpikeyword-filteringrst-injection

China's Great Firewall showed anomalous inconsistency: 13 test vectors produced mixed outcomes—TCP RST injection on some executions and a clean server response on others—with circumvention rates between 10% and 35% across 100 executions per vector. The authors attribute this to heterogeneous GFW infrastructure components applying different HTTP parsing logic, a departure from the GFW's usual consistency.

2024-m-ller-turning §5.2 dpirst-injectionkeyword-filteringmiddlebox-interference

China's GFW exhibited unusually inconsistent HTTP censorship behavior: 13 of the evaluated HRS test vectors circumvented the GFW in some executions but not others, with per-vector success rates between 10% and 35% across 100 executions per domain. The authors attribute this to two distinct parts of GFW infrastructure employing different HTTP censorship mechanisms, a departure from the GFW's typical consistency.

2024-niere-http-smuggling §5.2 (China paragraph), §5 intro dpirst-injectionkeyword-filtering

Extending Geneva's genetic algorithm to the application layer automatically discovered 77 unique HTTP evasion strategies and 9 DNS evasion strategies against censors in China, India, and Kazakhstan — all requiring only unprivileged usermode modifications with no TCP/IP header access. Against India's Airtel censor, 56 of the 77 strategies succeeded; 29 worked against Kazakhstan; 22 evaded China's keyword-based HTTP censorship and 27 evaded its Host-header censorship.

2022-harrity-get §5.1, §6 dpikeyword-filteringrst-injectiondns-poisoning

The GFW only inspects two locations within an HTTP request for censored keywords: the path component of the request line and the Host header, in UTF-8 and GB 18030 encodings (with %-decoding applied). Cookie headers, custom headers (e.g., X-Tension), and POST body fields are not monitored. Even in monitored positions, only approximately 75% of requests containing censored keywords actually trigger a TCP RST disconnection.

2021-rambert-chinese §4.4 keyword-filteringdpirst-injection