Transcript Franking for Encrypted Messaging
Armin Namavari, Thomas Ristenpart

TL;DR
This paper introduces transcript franking, a cryptographic protocol enabling secure reporting of message subsets in encrypted messaging, ensuring message causality and content verification for abuse mitigation.
Contribution
It presents the first formal definition, constructions, and security proofs for transcript franking in both two-party and group messaging contexts.
Findings
Efficient cryptographic constructions for transcript franking.
Formal security proofs for the proposed protocols.
Discussion on real-world deployment considerations.
Abstract
Message franking is an indispensable abuse mitigation tool for end-to-end encrypted (E2EE) messaging platforms. With it, users who receive harmful content can securely report that content to platform moderators. However, while real-world deployments of reporting require the disclosure of multiple messages, existing treatments of message franking only consider the report of a single message. As a result, there is a gap between the security goals achieved by constructions and those needed in practice. Our work introduces transcript franking, a new type of protocol that allows reporting subsets of conversations such that moderators can cryptographically verify message causality and contents. We define syntax, semantics, and security for transcript franking in two-party and group messaging. We then present efficient constructions for transcript franking and prove their security. Looking…
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Taxonomy
TopicsAdvanced Authentication Protocols Security · User Authentication and Security Systems · Advanced Malware Detection Techniques
