Towards Portable Identities in the Matrix Protocol

In this paper we present a cryptographic challenge-response authentication mechanism to enable portable identities within the Matrix protocol. Online instant communication systems like Matrix connect people in a convenient and cost-effective manner. However, most of today's communication infrastructure relies on inherently centralized infrastructure. Matrix currently, takes a federated approach instead. However, to fully decentralize the Matrix network, further actions must take place. Among others, a user's identity must be disconnected from the server they used to sign up and happen to communicate on. As part of this effort, a challenge-response authentication mechanism has been implemented that allows user IDs to be usable on any server, even if the a user's homeserver becomes unreachable.