TOM-Skype keyword list encryption evolved from a simple XOR cipher in versions 3.6/3.8 to 256-bit AES-ECB in versions 5.0/5.1. Surveillance traffic was encrypted with DES-ECB using hardcoded ASCII keys embedded in the binary (SURVEIL_KEY4.0 = 'X7sRUjL\0'; SURVEIL_KEY3.6 = '32bnx23l'), both recovered via known-plaintext attack and DLL injection respectively.

TOM-Skype maintains two separate encrypted keyword lists: one triggering both message suppression and silent upload to a Chinese server, and a second triggering surveillance only. Version 5.1.4.10 introduced a distinct surveillance-only keyfile downloaded from a separate URL (skypetools.tom.com/agent/keyfile_u), allowing the censor to monitor users without alerting them via censorship.

§2.1–§2.2 detection

The TOM-Skype keyword blacklist contained numerous user-coined neologisms added after the originals were censored—e.g., 'Lu Si' (a homophone for the Tiananmen date '64') and 'Oscar best actor winner' (a euphemism for Wen Jiabao)—demonstrating an adversarial arms race in which evasion vocabulary spreads freely until censors detect and blacklist the neologisms. The authors observed that some sensitive concepts (e.g., '64' rendered as '32+32' or '8 squared') spawn so many variants that the neologism strategy may not scale for the censor.

§4 (Conjecture 5) detection

The TOM-Skype censorship keyfile was substantially updated on 4/22/2011—possibly correlated with US-China human rights talks on 4/27–4/28/2011—and contained exact phrases lifted verbatim from 2011 Jasmine Revolution protest coordination documents, including specific intersection meeting points such as 'McDonald's in front of Chunxi Road in Chengdu'. This demonstrates real-time, operationally targeted keyword blacklisting within days of new coordination material appearing.

§3 detection

The 158-word surveillance-only keyword list in TOM-Skype 5.1.4.10 focused predominantly on specific Beijing demolition sites and addresses (e.g., 'Ling Jing Alley demolition'), plus five Shouwang church keywords—none of which triggered message suppression. Messages matching these keywords were silently uploaded to a server, demonstrating that the censor operates event-specific surveillance lists targeting localized grievance communities independent of its censorship blacklist.

§3 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