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.

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.

§4.2 evaluation

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

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

During the June 2025 shutdown, Iranian authorities blocked international One-Time Password (OTP) SMS delivery, preventing new sign-ins to foreign secure-messaging platforms and VPN services. This forced users toward government-approved domestic platforms that lack security and privacy protections. The blockade of OTPs effectively weaponized account-recovery flows as a secondary shutdown layer, disproportionately affecting users who needed to activate new circumvention tools during the crisis.

2025-iran-shutdown-measurement §Human Rights Implications port-blockingdpikeyword-filtering

Simple character-level perturbations (English) and homophone substitutions (Chinese), combined with LLM instruction-following prompts directing the model to use word substitutions in its output, successfully bypassed all input and output filters for all 41 input-blocked and 197 output-blocked queries across five major Chinese LLM services (Baidu-Chat, DeepSeek, Doubao, Kimi, Qwen). Every input-blocked query contained at least one keyword combination that alone triggered the filter, confirming keyword-matching rather than semantic classification.

2026-ablove-characterizing §VII-D keyword-filtering

Cross-national experiments conducted from Singapore, South Korea, and Taiwan during February 19–24, 2025 found no variance in blocking implementations, event syntax, or server infrastructure across all five Chinese LLM services. Input blocking was enacted identically in all three international locations, and services connected to the exact same server IP addresses globally — Kimi and Baidu-Chat connected to identical IPs and DeepSeek to the same two addresses across all tested locations.

2026-ablove-characterizing §VIII-A keyword-filtering

Input blocking in Chinese LLM services (DeepSeek, Qwen, Kimi, Doubao) is overwhelmingly consistent: all four services persistently block the exact same queries across all 5 measurement samples in both Simplified and Traditional Chinese. Output blocking is far less consistent, with only 29 out of 349 output-blocked queries blocked across all 5 samples. Baidu-Chat is exceptional: it performs almost no input blocking but instead relies heavily on post-search and output blocking (78.6% of blocks are output-phase).

2026-ablove-characterizing §VI-B keyword-filteringdpi

DeepSeek, Kimi, and Doubao all transmit analytics logs to the same Autonomous System (AS24429, Zhejiang Taobao Network Co., Ltd., a ByteDance/Volcengine subsidiary), with one monitoring endpoint IP directly overlapping between DeepSeek and Doubao. Additionally, all four non-Qwen services maintain connections with servers physically located in China throughout the chat session, transmitting user IDs, session IDs, viewport data, language preferences, and in Baidu-Chat's case, the full query text via URL-encoded CAPTCHA requests.

2026-ablove-characterizing §VI-D keyword-filtering

All five Chinese LLM services transmit partial or complete responses to the client machine even when output blocking is triggered, representing a major information leak. For DeepSeek and Qwen, truncated blocked responses are on average close in token length to full successful responses. For Baidu-Chat, the complete response is transmitted to the client but only partially rendered in the browser UI, with only a word or two visible on screen.

2026-ablove-characterizing §VI-C keyword-filtering