Fast message franking: From invisible salamanders to encryptment

Yevgeniy Dodis, Paul Grubbs, Thomas Ristenpart, Joanne Woodage

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Message franking enables cryptographically verifiable reporting of abusive messages in end-to-end encrypted messaging. Grubbs, Lu, and Ristenpart recently formalized the needed underlying primitive, what they call compactly committing authenticated encryption (AE), and analyze security of a number of approaches. But all known secure schemes are still slow compared to the fastest standard AE schemes. For this reason Facebook Messenger uses AES-GCM for franking of attachments such as images or videos. We show how to break Facebook’s attachment franking scheme: a malicious user can send an objectionable image to a recipient but that recipient cannot report it as abuse. The core problem stems from use of fast but non-committing AE, and so we build the fastest compactly committing AE schemes to date. To do so we introduce a new primitive, called encryptment, which captures the essential properties needed. We prove that, unfortunately, schemes with performance profile similar to AES-GCM won’t work. Instead, we show how to efficiently transform Merkle-Damgärd-style hash functions into secure encryptments, and how to efficiently build compactly committing AE from encryptment. Ultimately our main construction allows franking using just a single computation of SHA-256 or SHA-3. Encryptment proves useful for a variety of other applications, such as remotely keyed AE and concealments, and our results imply the first single-pass schemes in these settings as well.

Original languageEnglish (US)
Title of host publicationAdvances in Cryptology – CRYPTO 2018 - 38th Annual International Cryptology Conference, 2018, Proceedings
EditorsAlexandra Boldyreva, Hovav Shacham
PublisherSpringer Verlag
Pages155-186
Number of pages32
ISBN (Print)9783319968834
DOIs
StatePublished - 2018
Event38th Annual International Cryptology Conference, CRYPTO 2018 - Santa Barbara, United States
Duration: Aug 19 2018Aug 23 2018

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume10991 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349

Other

Other38th Annual International Cryptology Conference, CRYPTO 2018
CountryUnited States
CitySanta Barbara
Period8/19/188/23/18

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science(all)

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  • Cite this

    Dodis, Y., Grubbs, P., Ristenpart, T., & Woodage, J. (2018). Fast message franking: From invisible salamanders to encryptment. In A. Boldyreva, & H. Shacham (Eds.), Advances in Cryptology – CRYPTO 2018 - 38th Annual International Cryptology Conference, 2018, Proceedings (pp. 155-186). (Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics); Vol. 10991 LNCS). Springer Verlag. https://doi.org/10.1007/978-3-319-96884-1_6