[Resource Topic] 2025/1052: How to Trace Viral Content in End-to-End Encrypted Messaging

Welcome to the resource topic for 2025/1052

Title:
How to Trace Viral Content in End-to-End Encrypted Messaging

Authors: Pedro Branco, Matthew Green, Aditya Hegde, Abhishek Jain, Gabriel Kaptchuk

Abstract:

We study the problem of combating viral misinformation campaigns in end-to-end encrypted (E2EE) messaging systems such as WhatsApp. We propose a new notion of Hop Tracking Signatures (HTS) that allows for tracing originators of messages that have been propagated on long forwarding paths (i.e., gone viral), while preserving anonymity of everyone else. We define security for HTS against malicious servers.

We present both negative and positive results for HTS: on the one hand, we show that HTS does not admit succinct constructions if tracing and anonymity thresholds differ by exactly one “hop”. On the other hand, by allowing for a larger gap between tracing and anonymity thresholds, we can build succinct HTS schemes where the signature size does not grow with the forwarding path. Our positive result relies on streaming algorithms and strong cryptographic assumptions.

Prior works on tracing within E2EE messaging systems either do not achieve security against malicious servers or focus only on tracing originators of pre-defined banned content.

ePrint: https://eprint.iacr.org/2025/1052

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