Transcript Franking for Encrypted Messaging

2025-07-25

AI Summary

Existing message franking schemes support only single-message reporting, failing to meet practical content moderation requirements that necessitate coordinated reporting of multiple related messages—thus creating a gap between security goals and real-world deployment. This paper introduces the first session-stamped franking protocol, enabling users to securely report arbitrary subsets of end-to-end encrypted conversations while allowing platforms to verify both causal ordering among reported messages and their content authenticity. The protocol integrates digital signatures, hash chains, and zero-knowledge proofs to simultaneously ensure integrity, privacy, and verifiability. We provide a formal security proof under standard cryptographic assumptions and demonstrate support for both pairwise and group messaging. Our work bridges a fundamental theoretical gap in multi-message reportability, delivering the first fully deployable solution—including a concrete implementation blueprint and operational guidelines—for scalable, privacy-preserving abuse reporting in encrypted messaging systems.

Technology Category

• Application Domains: Security
• Natural Language Processing: Safety and Robustness
• Multiagent Systems: Agent Communication

Application Category

• Security and Privacy: Data transparency and provenance
• Responsible Web: Data and user privacy-enhancing technologies for the Web
• Web Mining and Content Analysis: Web data provenance, reliability, and authenticity

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 toward deployment considerations, we provide detailed discussion of how real-world messaging systems can incorporate our protocols.

Problem

• Enables secure reporting of multiple harmful messages in E2EE platforms
• Bridges gap between single-message and practical multi-message reporting needs
• Introduces cryptographic verification for conversation subsets and causality

Innovation

• Transcript franking enables multi-message abuse reporting
• Cryptographically verifies message causality and contents
• Efficient constructions for two-party and group messaging