Generalised Likelihood Ratio Testing Adversaries through the Differential Privacy Lens
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Differential Privacy (DP) provides tight upper bounds on the capabilities of optimal adversaries, but such adversaries are rarely encountered in practice. Under the hypothesis testing/membership inference interpretation of DP, we examine the Gaussian mechanism and relax the usual assumption of a Neyman-Pearson-Optimal (NPO) adversary to a Generalized Likelihood Test (GLRT) adversary. This mild relaxation leads to improved privacy guarantees, which we express in the spirit of Gaussian DP and (ε, δ)-DP, including composition and sub-sampling results. We evaluate our results numerically and find them to match the theoretical upper bounds.
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