Making messaging interoperability with third parties safe for users in Europe

What this post added

This post details the technical implementation of messaging interoperability for WhatsApp and Messenger to comply with the EU's Digital Markets Act (DMA). It describes the use of the Signal Protocol for end-to-end encryption, the construction of message protobuf structures encrypted and packaged into XML stanzas, and the client/server architecture for interoperation. Key technical aspects include the use of XMPP for client-to-server communication, HTTP for interfacing with third-party servers, OpenID and JWT for user identifier authentication, and the Noise Protocol Framework for client-to-server encryption. It also discusses the trade-offs and challenges of not having direct control over both sending and receiving clients, and explores an alternative proxy-based approach.