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In Differential Privacy, There is Truth: on Vote-Histogram Leakage in Ensemble Private Learning
JIAQI WANG · Roei Schuster · I Shumailov · David Lie · Nicolas Papernot

Thu Dec 01 09:00 AM -- 11:00 AM (PST) @ Hall J #731
When learning from sensitive data, care must be taken to ensure that training algorithms address privacy concerns. The canonical Private Aggregation of Teacher Ensembles, or PATE, computes output labels by aggregating the predictions of a (possibly distributed) collection of teacher models via a voting mechanism. The mechanism adds noise to attain a differential privacy guarantee with respect to the teachers' training data. In this work, we observe that this use of noise, which makes PATE predictions stochastic, enables new forms of leakage of sensitive information. For a given input, our adversary exploits this stochasticity to extract high-fidelity histograms of the votes submitted by the underlying teachers. From these histograms, the adversary can learn sensitive attributes of the input such as race, gender, or age. Although this attack does not directly violate the differential privacy guarantee, it clearly violates privacy norms and expectations, and would not be possible $\textit{at all}$ without the noise inserted to obtain differential privacy. In fact, counter-intuitively, the attack $\textbf{becomes easier as we add more noise}$ to provide stronger differential privacy. We hope this encourages future work to consider privacy holistically rather than treat differential privacy as a panacea.

Author Information

JIAQI WANG (University of Toronto)
Roei Schuster (Cornell Tech, Tel Aviv University)
I Shumailov (University of Toronto)
David Lie (University of Toronto)
Nicolas Papernot (University of Toronto and Vector Institute)

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