Abstract
Signal is the first application that applies the double ratchet for its end-to-end encryption protocol. The core of the double ratchet protocol is then applied in WhatsApp, the most popular messaging application around the world. Asynchronous Ratchet Tree (ART) is extended from ratchet and Diffie-Hellman tree. It is the first group protocol that applies Forward Secrecy (FS) with Post-Compromised Security (PCS). However, it does not consider protecting the privacy of user identity. Therefore, it makes sense to provide anonymous features in the conditions of FS and PCS. In this paper, the concepts of Internal Group Anonymity (IGA) and External Group Anonymity (EGA) are formalized. On the basis of IGA and EGA, we develop the “Anonymous Asynchronous Ratchet Tree (AART)” to realize anonymity while preserving FS and PCS. Then, we prove that our AART meets the requirements of IGA and EGA as well as FS and PCS. Finally, the performance and related issues of AART are discussed.
Highlights
WeChat is the second Instant Messaging (IM) application of China, and LINE is popular in East Asian countries
We develop the structure of Asynchronous Ratchet Tree (ART) to satisfy Internal Group Anonymity (IGA) security and apply the one-time address [8] to achieve the security of External Group Anonymity (EGA)
We propose a multi-stage anonymous group messaging protocol called
Summary
With the help of Internet development, Instant Messaging (IM) applications are much important in people’s lives. WhatsApp is the most popular IM application around the world with more than 2 billion active users. The third is WeChat with about 1 billion. In 2018, people spent 27.6 h a week online, of which 15.6% was used for instant messaging. WeChat is the second IM application of China, and LINE is popular in East Asian countries
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