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Causal Awareness in End-to-End Encrypted Group Messaging
eprint.iacr.orgpaper

Causal Awareness in End-to-End Encrypted Group Messaging

Cryptography paper that extends Chen and Fischlin's two-user Signal analysis (Eurocrypt 2024) to group chats. It introduces "causal awareness": a receiver can reconstruct part of the causal context in which an accepted message was sent. Network delay or adversarial interference can otherwise show an authentic message in a misleading context. Senders transmit records of what they have sent and received, and receivers verify these records and compare them with their own. The paper gives correctness and security definitions parameterized by how much causal information must be recovered, baseline constructions with proofs, and checkpoint-aided and server-aided variants. It also discusses how to surface this information in a messenger's UI.

TL;DR Formal framework and constructions letting E2EE group messengers detect message ordering and concurrency, so delayed or manipulated messages can't appear in a misleading context.
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Organisations named here

  • causal awareness
  • Chen and Fischlin

Technologies named here

  • Signal
  • Lamport clocks
  • Instant messengers in general
  • Vector clocks
  • Causal awareness framework

Techniques named here

  • Causal awareness
  • Checkpoint-aided variant of the framework
  • Server-aided variant of the framework

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