When the GFC keyword blacklist is known, multiple server-side-only evasion techniques become viable requiring no client modification: IP packet fragmentation to split keywords across MTU boundaries, HTML comment injection mid-keyword (e.g., 'Fa<!- Comment ->lun Gong'), alternative URL percent-encodings (e.g., 'F%61lun Gong'), and spam-style character substitution ('F@1un G0-ng'); the GFC implementation was observed not to check control characters in URL requests.

ChinaNET (CHINANET-*) performed 324/389 = 83.3% of all filtering observed across 296 probed hosts over a two-week period, and 99.1% of all filtering that occurred at the first hop past the Chinese border, despite constituting only 77% of first-hop routers encountered.

§3.3.1 evaluation

GFC keyword filtering exhibits strong diurnal patterns in which filtering effectiveness drops markedly during busy network periods, sometimes letting more than one fourth of packets containing known filtered keywords pass through unimpeded; the blocking timeout after a keyword RST was measured at 90 seconds for the tested route.

§3.2 detection

GFC keyword filtering is distributed across the backbone, not confined to border routers: only 29.6% of filtering occurred at the first hop into China's address space, 11.8% occurred beyond the third hop (with as many as 13 hops past the border in one case), and 28.3% of the 296 probed Chinese hosts were reachable via paths with no filtering at all.

§3.3 detection

Latent semantic analysis applied to the Chinese-language Wikipedia (942,033 terms across 94,863 documents, k=600 rank reduction) discovered 122 previously unknown GFC-filtered keywords starting from only 12 seed concepts; each list of 2,500 candidate terms required 1.2–6.7 hours to probe, with an average of 3.5 hours.

§4.3 evaluation

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