2015-narayanan-no
findings extracted from this paper
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The Encore system collected censorship measurements from 88,260 distinct IP addresses across 170 countries over seven months via installations by at least 17 volunteer website operators. China, India, the United Kingdom, and Brazil each contributed at least 1,000 measurements; Egypt, South Korea, Iran, Pakistan, Turkey, and Saudi Arabia each contributed more than 100.
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The paper identifies a structural conflict between Internet research's scalability imperative — where a project processing millions of devices is considered superior — and human-subjects ethics frameworks designed to minimize the number of people exposed to risk. Under U.S. law, Encore is compliant because it exploits known, intentional web functionality (the same-origin policy's cross-origin request mechanism) and provides an opt-out mechanism, but the authors note this compliance does not transfer to all jurisdictions where measurements occur.
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ACM SIGCOMM 2015's program committee accepted the Encore paper with an unprecedented 'signing statement' after heated ethical debate. The committee's core objections were: (1) users accessing censored URLs might face repercussions in regimes without due process; (2) most users under censorship would be unlikely to consent to the measurements; and (3) unlike ad-tracker third-party requests, Encore requests do not reflect any user intent.
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To mitigate harm, Encore restricted its URL list to Twitter, Facebook, and YouTube on the grounds that widgets from these domains appear in ordinary web browsing, making Encore-induced cross-origin requests statistically indistinguishable from normal traffic. The authors argued that this renders the risk comparable to baseline browsing, though the SIGCOMM committee disputed whether contextual equivalence with ad-tracking constitutes adequate ethical justification.
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Encore's architecture turns ordinary web visitors into measurement vantage points, which the researchers argue prevents censors from detecting and disabling dedicated measurement probes. However, this benefit comes with the trade-off that the individuals whose browsers are co-opted face potential legal or physical risk that differs by country and by the specific censored content accessed.