FAQ
Questions you might have about the Cassis protocol.
What problem does Cassis solve?
Bitcoin is scaling through layers: Lightning, Liquid, Arkade, Cashu, Fedimint and others being invented every day. A user of one of these networks can't pay someone on the other. Currently, the developers of such solutions have hacked a bridge solution using a centralized swap provider or Lightning gateway.
Cassis abstracts the swap part into the pure HTLC level, makes it into an open and interoperable protocol that any of these networks can participate in and enables multi-hop routing. One can use Lightning where it makes sense, pay directly between Liquid and Cashu, or hop through two different Fedimint bridges before reaching the receiver at Arkade.
Can a router steal my payment?
No. A router cannot redeem an HTLC without the preimage such that sha256(R) == payment_hash, and it cannot produce that preimage without the receiver revealing it. Once the receiver reveals it that is equivalent to the receiver issuing a receipt for the payment.
Every hop is enforced by the network it sits on, using that layer's own HTLC construction, so the guarantee does not depend on the router's honesty. Each individual network can have bugs in its logic or be controlled by some malicious actor that may steal the HTLC, but that loss is part of the risk each router accepts when they decide to bridge that specific network.
Does this system need its own wallet?
Cassis is expected to be integrated into existing wallets for each layer.
Why not just use Lightning?
Lightning currently serves the purpose of being the glue between some of the existing layers, and because of its prevalence it's expected to play an important role in Cassis too. But we need a system that is generic and doesn't require Lightning and can evolve without it, if that's necessary.
For networks like Bark and Spark, for example, the Lightning gateway is centralized and can't be opted out. For Fedimint it is in theory open, but most federations end up using the same gateway. Arkade has had problems in the past with their Lightning gateway going out of business, and the barrier of entry for running a Cashu mint is severely higher today because it requires every mint operator to run its own Lightning node. In all these cases, Cassis can be simpler and better solution.
Does Cassis need a new invoice format?
Yes, in a way, but it can also be hacked into the BOLT11 Lightning invoice so both methods of payment are supported at first.
At the same time we are working on a related invoicing method called Cassis Order Protocol (COP) that will allow much more flexible and rich payment flows using a common simple interface. This is very early stages, but more information will be published at https://cop.cassis.cash/.
Is Cassis safe to use yet?
It is experimental software under active development. The protocol logic is small and auditable, but the implementation is young. Only put in money you are comfortable losing, see the quickstart.