Blocking all homophones of 422 censored keywords would generate approximately 47,000 false-positive weibos per day per keyword, totaling roughly 20 million false positives daily — approximately 20% of Sina Weibo's daily message volume — making blanket homophone blocklisting operationally infeasible without massive collateral censorship of innocent traffic.

Homophone-transformed weibos lasted on Sina Weibo an average of 3.94 hours (σ=5.51) before removal, versus 1.3 hours (σ=1.25) for unaltered originally-censored posts — a threefold difference (W=1830, p<0.01) — while ultimate censorship rates were not significantly different between conditions.

Experiment 1 / Results evaluation

Falling back to human review to defeat the homophone technique would cost the Sina Weibo censorship apparatus more than 15 additional human-hours per day per censored keyword — derived from an efficient censorship worker reading approximately 50 weibos per minute (Zhu et al. 2013) applied to ~47,000 daily false-positive matches per keyword — a burden that scales with the number of simultaneously banned keywords, which may number in the thousands.

Analysis: Cost to adversaries (RQ3) evaluation

Replacing censored keywords with algorithmically-generated homophones increased the initial publication rate on Sina Weibo from 90.79% for unaltered posts to 94.74% for transformed posts (χ²=6.219, p=0.01), demonstrating that the technique successfully bypasses automatic keyword matching at the publication gate even when posts are ultimately censored at similar rates.

Experiment 1 / Results — Table 1 evaluation

Native Chinese-speaking Amazon Mechanical Turk workers understood the content of 605 out of 608 homophone-transformed posts (99.51%), with only 2.85% of all impressions (52/1,824) reporting difficulty; workers unable to identify transformed keywords were significantly more likely to report confusion (p<0.001 for original keywords, p=0.03 for transformed keywords).

Experiment 2 / Results — Table 2 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