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Paper: Asymmetric Message Franking: Content Moderation for Metadata-Private End-to-End Encryption

Authors:
Nirvan Tyagi
Paul Grubbs
Julia Len
Ian Miers
Thomas Ristenpart
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DOI: 10.1007/978-3-030-26954-8_8
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Abstract: Content moderation is crucial for stopping abusive and harassing messages in online platforms. Existing moderation mechanisms, such as message franking, require platform providers to be able to associate user identifiers to encrypted messages. These mechanisms fail in metadata-private messaging systems, such as Signal, where users can hide their identities from platform providers. The key technical challenge preventing moderation is achieving cryptographic accountability while preserving deniability.In this work, we resolve this tension with a new cryptographic primitive: asymmetric message franking (AMF) schemes. We define strong security notions for AMF schemes, including the first formal treatment of deniability in moderation settings. We then construct, analyze, and implement an AMF scheme that is fast enough to use for content moderation of metadata-private messaging.
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BibTeX
@article{crypto-2019-29915,
  title={Asymmetric Message Franking: Content Moderation for Metadata-Private End-to-End Encryption},
  booktitle={Advances in Cryptology – CRYPTO 2019},
  series={Lecture Notes in Computer Science},
  publisher={Springer},
  volume={11694},
  pages={222-250},
  doi={10.1007/978-3-030-26954-8_8},
  author={Nirvan Tyagi and Paul Grubbs and Julia Len and Ian Miers and Thomas Ristenpart},
  year=2019
}