DPSW-Sketch: A Differentially Private Sketch Framework for Frequency Estimation over Sliding Windows (Technical Report)

TL;DR

This paper introduces DPSW-Sketch, a differentially private framework for accurately estimating item frequencies and identifying heavy hitters in streaming data over sliding windows, balancing privacy and utility efficiently.

Contribution

It presents a novel differentially private sketch framework based on count-min sketch for sliding windows, improving utility-privacy trade-offs over existing methods.

Findings

Provides accurate frequency and heavy hitter estimates with bounded errors.

Operates in sublinear time and space relative to window size.

Outperforms state-of-the-art methods in experiments.

Abstract

The sliding window model of computation captures scenarios in which data are continually arriving in the form of a stream, and only the most recent $w$ items are used for analysis. In this setting, an algorithm needs to accurately track some desired statistics over the sliding window using a small space. When data streams contain sensitive information about individuals, the algorithm is also urgently needed to provide a provable guarantee of privacy. In this paper, we focus on the two fundamental problems of privately (1) estimating the frequency of an arbitrary item and (2) identifying the most frequent items (i.e., \emph{heavy hitters}), in the sliding window model. We propose \textsc{DPSW-Sketch}, a sliding window framework based on the count-min sketch that not only satisfies differential privacy over the stream but also approximates the results for frequency and heavy-hitter queries within bounded errors in sublinear time and space w.r.t.~$w$. Extensive experiments on five real-world and synthetic datasets show that \textsc{DPSW-Sketch} provides significantly better utility-privacy trade-offs than state-of-the-art methods.