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Poster

Continual Counting with Gradual Privacy Expiration

Joel Daniel Andersson · Monika Henzinger · Rasmus Pagh · Teresa Steiner · Jalaj Upadhyay

West Ballroom A-D #6203
[ ]
[ Paper [ Poster [ OpenReview
Thu 12 Dec 11 a.m. PST — 2 p.m. PST

Abstract: Differential privacy with gradual expiration models the setting where data items arrive in a stream and at a given time t the privacy loss guaranteed for a data item seen at time (td) is ϵg(d), where g is a monotonically non-decreasing function. We study the fundamental *continual (binary) counting* problem where each data item consists of a bit and the algorithm needs to output at each time step the sum of all the bits streamed so far. For a stream of length T and privacy *without* expiration continual counting is possible with maximum (over all time steps) additive error O(log2(T)/ε) and the best known lower bound is Ω(log(T)/ε); closing this gap is a challenging open problem. We show that the situation is very different for privacy with gradual expiration by giving upper and lower bounds for a large set of expiration functions g. Specifically, our algorithm achieves an additive error of O(log(T)/ϵ) for a large set of privacy expiration functions. We also give a lower bound that shows that if C is the additive error of any ϵ-DP algorithm for this problem, then the product of C and the privacy expiration function after 2C steps must be Ω(log(T)/ϵ). Our algorithm matches this lower bound as its additive error is O(log(T)/ϵ), even when g(2C)=O(1).Our empirical evaluation shows that we achieve a slowly growing privacy loss that has significantly smaller empirical privacy loss for large values of d than a natural baseline algorithm.

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