Generic Anonymity Wrapper for Messaging Protocols

Modern messengers use advanced end-to-end encryption protocols to protect message content even if user secrets are ever temporarily exposed. Yet, encryption alone does not prevent user tracking, as protocols often attach metadata, such as sequence numbers, public keys, or even plain user identifiers. This metadata reveals the social network as well as communication patterns between users. Existing protocols that hide metadata in Signal (i.e., Sealed Sender), for MLS-like constructions (Hashimoto et al., CCS 2022), or in mesh networks (Bienstock et al., CCS 2023) are relatively inefficient or specially tailored for only particular settings. Moreover, all existing practical solutions reveal crucial metadata upon exposures of user secrets.