A censor tracking which deleted posts are resurrected can apply Bayesian inference to identify content-preservation system users: for each resurrected post r observed by set O(r), each observer's suspicion score updates by factor (|O(r)|−1)/|O(r)|, while observers of non-resurrected deletions can be ruled out with certainty. The attack requires only that the censor join the preservation system with a few sock-puppet accounts spread across multiple followed-user lists.

A censor with platform-side control can definitively confirm a single suspected user by injecting a unique fake post visible only to that user, then querying the preservation system for resurrected posts attributed to that fabricated author. Presence of the fake post in the resurrection feed is binary confirmation of user membership. This targeted attack defeats automated post-alteration countermeasures when a human examines the result.

§5.1 detection

Simulation on a 1,000,000-user scale-free Weibo topology shows that at 1% GhostPost user adoption the system preserves over 70% of postviews against the daytime censor (2-hour median deletion) and nearly 90% against the nighttime censor (10-hour median deletion). Even a highly aggressive censor deleting posts within 30 minutes on average cannot prevent a 1.5% GhostPost deployment from resurrecting the majority of postviews. Steep coverage gains plateau around 0.5% adoption, after which marginal returns diminish.

§4.2, Figure 1 evaluation

GhostPost's client-server coordination channel transfers only metadata and small text payloads, making it neither bandwidth-intensive nor latency-sensitive. The paper explicitly concludes that 'practically any means of communication, including low-performance covert channels, are adequate' for the coordination channel, enabling operation over DNS tunnels, steganographic channels, or other constrained transports when the central server's HTTPS endpoint is blocked.

§2.1 defense

Sina Weibo's deletion workforce exhibits strong diurnal variation: posts published 3–9 AM have median lifetimes of 8–9 hours, while posts from 10 AM–midnight have median lifetimes around 2 hours. Over 90% of eventually-deleted posts are removed within 24 hours, but the nighttime slowdown creates a predictable window where post survival is 4–5× longer than daytime.

§4.2 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