WeChat, Alibaba Wangwang, Zhihu, and Sina Weibo all implement keyword combination filtering — messages are blocked only when every component of a blacklisted combination appears simultaneously, regardless of order. This allows censors to target sensitive contexts (e.g., 习近平 + 三连任 [Xi Jinping + three consecutive terms]) without filtering neutral mentions of individual terms.

The component-aware binary splitting algorithm (CompAwareBinSplit) requires on average 35.47 messages per article to isolate a sensitive keyword combination — 10.3% as many as the 342.72 required by the previously used algorithm — and is the only evaluated algorithm that correctly handles overlapping keyword components and multiple co-occurring combinations.

§5.4, §6, Table 1 evaluation

The previously used bisection algorithm required an average of 342.72 messages per news article to isolate a triggering keyword combination, and produced incorrect results in 44% of test cases — primarily because the Unilateral Elimination Flaw caused it to miss components that appeared multiple times in an article.

§4, §6 evaluation

Server-side keyword enumeration on Chinese platforms has become increasingly uneconomical: platforms now require non-virtual phone numbers for account registration, and test accounts are banned after sending a threshold volume of sensitive content. The paper's 5,521-article dataset and 1,956 confirmed keyword combinations were collected via sample testing between September 2017 and October 2018, with registration costs being the primary limiting factor for research scale.

§1, §7 deployment

WeChat censors messages even when keyword components overlap within the message text — e.g., the combination 帶來 + 調整 + 整體 + 領域 triggers filtering in the fused form 帶來abc調整體xyz領域 where 調整 and 整體 share a character. No previously published algorithm correctly identified overlapping components; only CompAwareBinSplit resolves this by advancing the search window from index i+1 rather than past the full matched span.

§4.2, §5.4 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