Federated Anonymous Blocklisting across Service Providers and its Application to Group Messaging

• URL: http://arxiv.org/abs/2511.03486v1
• Date: Wed, 05 Nov 2025 14:11:46 GMT
• Title: Federated Anonymous Blocklisting across Service Providers and its Application to Group Messaging
• Authors: David Soler, Carlos Dafonte, Manuel Fernández-Veiga, Ana Fernández Vilas, Francisco J. Nóvoa,
• Abstract summary: In Anonymous Blocklisting schemes, users must prove during authentication that none of their previous pseudonyms has been blocked.<n>We propose an alternative textitFederated Anonymous Blocklisting (FAB) in which the centralised Service Provider is replaced by small distributed Realms.
• Score: 1.7616042687330637
• License: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Abstract: Instant messaging has become one of the most used methods of communication online, which has attracted significant attention to its underlying cryptographic protocols and security guarantees. Techniques to increase privacy such as End-to-End Encryption and pseudonyms have been introduced. However, online spaces such as messaging groups still require moderation to prevent misbehaving users from participating in them, particularly in anonymous contexts.. In Anonymous Blocklisting (AB) schemes, users must prove during authentication that none of their previous pseudonyms has been blocked, preventing misbehaving users from creating new pseudonyms. In this work we propose an alternative \textit{Federated Anonymous Blocklisting} (FAB) in which the centralised Service Provider is replaced by small distributed Realms, each with its own blocklist. Realms can establish trust relationships between each other, such that when users authenticate to a realm, they must prove that they are not banned in any of its trusted realms. We provide an implementation of our proposed scheme; unlike existing AB constructions, the performance of ours does not depend on the current size of the blocklist nor requires processing new additions to the blocklist. We also demonstrate its applicability to real-world messaging groups by integrating our FAB scheme into the Messaging Layer Security protocol.

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