Paper

{
  "raw_xml": "<entry>\n    <id>http://arxiv.org/abs/2602.17454v1</id>\n    <title>Privacy in Theory, Bugs in Practice: Grey-Box Auditing of Differential Privacy Libraries</title>\n    <updated>2026-02-19T15:18:00Z</updated>\n    <link href='https://arxiv.org/abs/2602.17454v1' rel='alternate' type='text/html'/>\n    <link href='https://arxiv.org/pdf/2602.17454v1' rel='related' title='pdf' type='application/pdf'/>\n    <summary>Differential privacy (DP) implementations are notoriously prone to errors, with subtle bugs frequently invalidating theoretical guarantees. Existing verification methods are often impractical: formal tools are too restrictive, while black-box statistical auditing is intractable for complex pipelines and fails to pinpoint the source of the bug. This paper introduces Re:cord-play, a gray-box auditing paradigm that inspects the internal state of DP algorithms. By running an instrumented algorithm on neighboring datasets with identical randomness, Re:cord-play directly checks for data-dependent control flow and provides concrete falsification of sensitivity violations by comparing declared sensitivity against the empirically measured distance between internal inputs. We generalize this to Re:cord-play-sample, a full statistical audit that isolates and tests each component, including untrusted ones. We show that our novel testing approach is both effective and necessary by auditing 12 open-source libraries, including SmartNoise SDK, Opacus, and Diffprivlib, and uncovering 13 privacy violations that impact their theoretical guarantees. We release our framework as an open-source Python package, thereby making it easy for DP developers to integrate effective, computationally inexpensive, and seamless privacy testing as part of their software development lifecycle.</summary>\n    <category scheme='http://arxiv.org/schemas/atom' term='cs.CR'/>\n    <published>2026-02-19T15:18:00Z</published>\n    <arxiv:comment>2026.3 PoPETS</arxiv:comment>\n    <arxiv:primary_category term='cs.CR'/>\n    <author>\n      <name>Tudor Cebere</name>\n    </author>\n    <author>\n      <name>David Erb</name>\n    </author>\n    <author>\n      <name>Damien Desfontaines</name>\n    </author>\n    <author>\n      <name>Aurélien Bellet</name>\n    </author>\n    <author>\n      <name>Jack Fitzsimons</name>\n    </author>\n  </entry>"
}