Poster
Continual Counting with Gradual Privacy Expiration
Joel Daniel Andersson · Monika Henzinger · Rasmus Pagh · Teresa Steiner · Jalaj Upadhyay
West Ballroom A-D #6203
Abstract:
Differential privacy with gradual expiration models the setting where data items arrive in a stream and at a given time the privacy loss guaranteed for a data item seen at time is , where 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 and privacy *without* expiration continual counting is possible with maximum (over all time steps) additive error and the best known lower bound is ; 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 . Specifically, our algorithm achieves an additive error of for a large set of privacy expiration functions. We also give a lower bound that shows that if is the additive error of any -DP algorithm for this problem, then the product of and the privacy expiration function after steps must be . Our algorithm matches this lower bound as its additive error is , even when .Our empirical evaluation shows that we achieve a slowly growing privacy loss that has significantly smaller empirical privacy loss for large values of than a natural baseline algorithm.
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