Building a RAPPOR with the Unknown: Privacy-Preserving Learning of Associations and Data Dictionaries

TL;DR

This paper introduces a novel decoding algorithm for RAPPOR that enables privacy-preserving estimation of unknown strings and their relationships without prior knowledge of the data dictionary.

Contribution

It presents a new method for estimating unknown data elements and their joint distributions in RAPPOR, enhancing privacy-preserving data analysis capabilities.

Findings

Effective estimation of unknown strings achieved

Joint distribution estimation of multiple variables demonstrated

Enhanced privacy guarantees with unknown data elements

Abstract

Techniques based on randomized response enable the collection of potentially sensitive data from clients in a privacy-preserving manner with strong local differential privacy guarantees. One of the latest such technologies, RAPPOR, allows the marginal frequencies of an arbitrary set of strings to be estimated via privacy-preserving crowdsourcing. However, this original estimation process requires a known set of possible strings; in practice, this dictionary can often be extremely large and sometimes completely unknown. In this paper, we propose a novel decoding algorithm for the RAPPOR mechanism that enables the estimation of "unknown unknowns," i.e., strings we do not even know we should be estimating. To enable learning without explicit knowledge of the dictionary, we develop methodology for estimating the joint distribution of two or more variables collected with RAPPOR. This is a critical step towards understanding relationships between multiple variables collected in a privacy-preserving manner.