Local-first Coordination via Friend-to-Friend Choreographies

We lay out a new choreographic model that, departing from point-to-point interactions, aims to harness local-first coordination of distributed applications. We dub our model \emph{friend-to-friend} choreographies since its main application domain are decentralised applications that guarantee confidentiality in a \emph{fully decentralised} setting. A key principle of local-first coordination is indeed that the control on computational resources is not given to third-parties. This yields a notion of projection different than those usually found in the literature since our projection operation aims to identify minimal sets of agents that should be aware of an interaction and so compute the cryptographic keys necessary to ensure confidentiality.Friend-to-friend choreographies have a straightforward implementation in \nb, a platform which provides a communication infrastructure and friend-to-friend decentralised storage.