研究开发者在隐私审计下如何策略性应对,提出更优的审计设计方法。
Differentially Private Auditing Under Strategic Response
- 将审计建模为双层博弈,考虑开发者对隐私约束的策略响应。
- 证明传统隐私分配方式会增加未检测到的危害,且效果更差。
- 提出SPAD算法,通过开发者最优响应计算超梯度优化审计策略。
监管机构对AI系统的审计越来越多地依赖差分隐私(DP)来保护训练数据和模型内部信息。本文研究当被审计开发者可对隐私受限的审计接口进行策略性响应时的审计设计问题。我们将隐私受限审计形式化为双层斯塔克尔伯格博弈:审计方先设定查询策略与各危害维度的DP预算分配,开发者则根据此响应重新分配缓解努力。我们引入福利加权漏检差距 $B_w$,衡量审计在开发者策略最优响应下未能检测到的真实残余危害。证明当有效可检测性异质、福利权重与可检测性不共单调,且开发者最优解为内点时,朴素的DP审计(均匀或按危害比例分配)会导致比无策略缓解基线更大的 $B_w$。我们刻画了最优审计分配需平衡福利权重、误检概率、可检测性弹性与缓解成本曲率四个因素,并通过开发者的KKT系统将双层问题转化为单层问题。提出战略隐私审计设计(SPAD),一种基于投影梯度的算法,利用开发者最优响应计算超梯度。
原文摘要 · Abstract (English)
Regulatory audits of AI systems increasingly rely on differential privacy (DP) to protect training data and model internals. We study audit design when the audited developer can strategically respond to the privacy-constrained audit interface. We formalize privacy-constrained auditing as a bilevel Stackelberg game, in which an auditor commits to a query policy and DP budget allocation across harm dimensions, and a strategic developer reallocates mitigation efforts in response. We introduce the welfare-weighted under-detection gap $B_w$, the welfare-weighted true residual harm the audit fails to detect at the developer's strategic best response, and prove that naive DP auditing (uniform or harm-proportional allocation) induces a strictly larger $B_w$ than any non-strategic mitigation baseline whenever effective detectability is heterogeneous, the welfare weights are not comonotone with detectability, and the developer's optimum is interior. We characterize the optimal auditor allocation as a four-factor balance of welfare weight, audit miss-probability, detectability elasticity, and mitigation-cost curvature, and provide a single-level reformulation of the bilevel problem via the developer's KKT system. We propose Strategic Private Audit Design (SPAD), a projected-gradient algorithm with hypergradients computed through the developer's best response.
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