Poster: Metadata-private Messaging without Coordination

Metadata-private messaging (MPM) refers to an end-to-end encrypted messaging system that protects not just the payload messages but also the privacy-revealing communication metadata, such as user identities, conversation frequencies, traffic volumes, etc. Protecting the communication metadata is challenging due to the existence of global adversaries that can monitor and even actively interfere with the traffic. Established systems like Tor are not adequate under such adversarial models. Thus, many academic systems have been proposed to push this frontier with different trade-offs among security, performance, and trust assumptions. Despite progress, one major limitation prevalent in almost all prior art is the requirement for messaging buddies to coordinate the time (also known as “dialing”) to start the conversation. Compared to traditional messaging systems, such coordination protocols, which must also be metadata private, are expensive for both user adoption and service operations. In this ongoing study, we propose to develop a new MPM system without coordination. Unlike prior art, we plan to model the MPM system into two separate modules: metadata-private notifications and metadata-private message retrieval, which is intuitively inspired by traditional messaging systems. We will instantiate these ideas by drawing insights from recent work about private signaling, oblivious message retrieval, and MPM under hardware trust. © 2023 Copyright held by the owner/author(s).