Practical Auditing of Differentially Private Graph Release Mechanisms: Methodology, Toolkit, and Case Study

Abstract

Differential Privacy (DP) has become a prominent approach for protecting graph data releases, yet empirical auditing methodologies have largely been developed for tabular datasets and machine learning pipelines rather than graph-structured outputs. We present a methodology for empirically auditing DP graph release mechanisms, identifying two graph-specific audit design problems: canary construction and witness statistic selection. We combine these components with an established statistically certified testing procedure and implement the resulting methodology as an open-source Python toolkit. To demonstrate the approach, we audit a published state-of-the-art Node-DP graph release mechanism. Across a series of synthetic and real-world canary pairs, we obtain certified lower bounds on the privacy parameter {\varepsilon} that exceed the claimed value, yielding counterexamples sufficient to falsify the claimed guarantee for the audited implementation. The violations persist under progressively stronger restrictions on the input domain, including non-empty and connected graphs. We also show that witness selection can materially affect whether a violation is detected, highlighting the importance of evaluating a diverse battery of statistics when auditing DP graph release mechanisms.