Cryptology ePrint Archive: Report 2021/1180

The Effect of False Positives: Why Fuzzy Message Detection Leads to Fuzzy Privacy Guarantees?

István András Seres and Balázs Pejó and Péter Burcsi

Abstract: Fuzzy Message Detection (FMD) is a recent cryptographic primitive invented by Beck et al. (CCS'21) where an untrusted server performs coarse message filtering for its clients in a recipient-anonymous way. In FMD --- besides the true positive messages --- the clients download from the server their cover messages determined by their false-positive detection rates. What is more, within FMD, the server cannot distinguish between genuine and cover traffic. In this paper, we formally analyze the privacy guarantees of FMD from three different angles. First, we analyze three privacy provisions offered by FMD: recipient unlinkability, relationship anonymity, and temporal detection ambiguity. Second, we perform a differential privacy analysis and coin a relaxed definition to capture the privacy guarantees FMD yields. Finally, we simulate FMD on real-world communication data. Our theoretical and empirical results assist FMD users in adequately selecting their false-positive detection rates for various applications with given privacy requirements.

Category / Keywords: cryptographic protocols / Fuzzy Message Detection, unlinkability, anonymity, differential privacy, game theory

Original Publication (in the same form): Financial Cryptography and Data Security 2022

Date: received 14 Sep 2021, last revised 6 Dec 2021

Contact author: seresistvanandras at gmail com, bupe at inf elte hu, pejo at crysys hu

Available format(s): PDF | BibTeX Citation

Version: 20211206:161556 (All versions of this report)

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