Cassis, a new simple scheme for generic multi-layer multi-hop HTLC routing

Arkade introduces the Intents protocol, which significantly simplifies the routing of payments by utilizing various solvers that operate on behalf of users. Similarly, Kaleidoswap is developing a network that leverages Hash Time Locked Contracts (HTLCs) to establish a more generic framework for Bitcoin transfers between different layers. Another noteworthy initiative is Cassis, which aims to implement a straightforward concept previously suggested by Giacomo Zucco. Cassis proposes a system where payments are conducted through a series of HTLCs linked by a common SHA-256 hash. This chain of contracts allows for the payments to unwind from the receiver backwards upon the revelation of a preimage.

This model presents several benefits including instant settlement options, reduced cost, and the feasibility of receiving funds while offline. It also empowers users to choose their desired balance between privacy, security, and custody by selecting appropriate layers for holding their funds without compromising their ability to conduct or receive payments. The flexibility of this system is further enhanced by allowing any node with assets in at least two layers to function as a routing node. This capability is illustrated through a multi-hop payment scenario involving nodes like FC, CL, and LA, facilitating a transaction from Peter to Rose across various intermediary layers.

The technical foundation for these operations is provided by a Rust implementation, which is accessible on GitHub. This implementation supports a range of layers including Lightning, Liquid, Cashu, Fedimint, Arkade, Rootstock, and traditional on-chain Bitcoin transactions. However, it remains a work in progress with several critical challenges yet to be addressed. Communication between nodes currently relies on non-standardized JSON messages over Iroh connections, and router announcements are merely made through public Nostr relays. Furthermore, establishing a reliable reputation system for routing nodes and senders is essential to prevent failures and financial losses associated with the reclamation of funds locked in unsuccessful HTLCs. Enhancements are also being made to develop a richer payment protocol distinct from the original plain JSON invoice format, which will utilize Iroh communication channels. Additionally, the potential for enabling offline receipt of funds through trusted third-party or federation mechanisms, similar to those used by Fedimint, is under consideration but has not been fully explored.