Introduction

Cassis relies on a central server, and yet it is not custodial. Or at least the server doesn't keep any custody of funds, but the entire thing works based on trust: not trust between users and the server, but between users and other users.

Let's take the example of Alice and Bob. They are friends and Bob is comfortable with Alice owing him 100,000 satoshis. Each will generate a Schnorr keypair and share the public keys with each other, then Bob will reach out to the Cassis server and send a signed message that says, roughly:

<bob>: TRUST <alice> 100000

And with that a trustline will be established between these two.

Now they can send transactions to each other using Cassis. First Alice can send transactions to Bob with

<alice>: TRANSFER <bob> 5000

and now Bob has up to 5,000 credit she can send back to Bob:

<bob>: TRANSFER <bob> 1337

And if you ask the Cassis server it will tell you right away that now Alice owes Bob 93663 satoshis.

This is all very simple, but it's not adding much. How do we do actual payments, transfers that aren't between close friends?