支援發送者匿名性和選擇性訊息存取的連續群組密鑰協議協定

Abstract

群組通訊應用程式重度依賴群組密鑰協定協議以確保安全性，但這些協議的隱私方面尚未被充分探討。當不受信任的第三方應用程式，例如聊天機器人，被整合進群組通訊時，這種疏忽可能會嚴重危及使用者隱私。本文旨在通過設計一種支持發送者匿名和選擇性訊息存取的群組密鑰協定協議，來提高群組通訊應用程式的隱私保證。我們首先在威脅模型中考慮不受信任的第三方應用程式，然後基於 IETF MLS 群組通訊標準，我們提出了一個捕捉這兩個隱私特性的安全模型。此外，我們基於 MLS 標準使用的 TreeKEM 密鑰協定協議提出了一個可行的實現方法。我們的方法造成的額外計算負擔不會隨著使用者數量增加，對聊天機器人數量則是線性成長，而模組化的設計使其便於整合進 MLS 標準。

Group messaging applications rely heavily on group key agreement protocols to ensure security, but the privacy aspects of these protocols have been underexplored. This oversight becomes particularly critical when untrusted third-party applications, the chatbots, are integrated into group chats, potentially compromising privacy. This paper aims to improve the privacy guarantee of group messaging applications by designing a group key agreement protocol that supports sender anonymity and message access control. We first consider untrusted third party applications in our threat model, then, based on the security model of the IETF MLS standard for group messaging, we propose a security model that captures the two privacy features. Furthermore, we propose a construction based on TreeKEM, the key agreement protocol used by MLS. Our construction imposes an overhead that is constant with respect to the number of users and linear with the number of chatbots, and the modular design makes it easy to integrate into the MLS standard.