2023-brown-augmenting
findings extracted from this paper
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DNS censorship complexity varies sharply by country: Iran injects static forged IPs exclusively from 10.0.0.0/8 and Turkmenistan uses only 127.0.0.1, making detection trivial, while China's constant fake-IP churn across ASes demands dynamic ML approaches; models trained without country-specific ASN features still perform well, enabling transfer to countries where GFWatch-equivalent infrastructure does not exist.
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By mapping ML-predicted censored probes back to their DNS response IPs, the authors discovered 748 forged IP addresses used by China's GFW as DNS blocking signatures that OONI's heuristics missed; supervised and unsupervised models also identified several ISP-specific injected IPs absent from even GFWatch's comprehensive signature list, demonstrating that static signature lists substantially undercount active GFW DNS censorship.
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OONI and Satellite (Censored Planet) agree on roughly 75% of tested Chinese domains as uncensored, but DNS anomaly agreement is poor: each platform flags fewer than 0.5% of domains as anomalous in any given biweekly window, and the two platforms frequently disagree on which domains are censored because China's GFW uses dynamic fake-IP injection that defeats static rule-based heuristics.
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XGBoost supervised models trained on DNS probe features achieve TPRs of 100% (Satellite) and 99.8% (OONI) at FPRs of 0.0% and 0.2% respectively when using platform-native anomaly labels; cross-source training with GFWatch labels applied to the same records yields 99.4% TPR for Satellite and 86.7% TPR for OONI, with SHAP analysis confirming that ASN and organization name of the returned DNS response IPs are the dominant predictive signal.
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Unsupervised one-class SVM models trained only on clean (uncensored) records detect GFW DNS censorship with 99.1% TPR at 17.4% FPR on Satellite data; over half of apparent false negatives are truly uncensored probes where the GFW transiently failed to inject a forged response, confirming that GFW DNS injection is not perfectly consistent at the individual probe level.