Abuse Reporting and Enforcement for Third Party Moderators in Private Messaging

We introduce new techniques for verifiable reporting of abusive messages in private messaging platforms. Our techniques are compatible with both metadata-hiding messaging systems, where the platform does not know who speaks to whom, and with third-party moderation, where the platform is not involved in the process of verifying or judging reported content.

While prior work in this space considers the question of how a moderator would verify reports, prior works do not address the question of how a moderator and platform would collaborate to enforce moderation decisions. In a setting where the platform does not wish to be involved in or responsible for enforcing moderation decisions, or in federated settings where it is not clear who would be responsible for enforcement, this presents an additional challenge.

Our work solves this problem with a lightweight credentialing and revocation mechanism that does not involve the platform in moderation enforcement at all. In order to support this added functionality, we build on Asymmetric Message Franking (Crypto '19) and improve performance over the original scheme, reducing moderator computation and communication costs to verify reports by $6\times$ and $7\times$, respectively.