A Decker-Wattenhofer MultiChannel For Reduced Inter-LSP Trust

The innovative MultiChannel and MultiPTLC constructions offer a new approach to achieving high availability, consistency, and partition tolerance within the Bitcoin Lightning Network. This development is aimed at ensuring users can access the Lightning Network anytime, enhancing the network's reliability. However, this advantage comes at the cost of reduced security for Lightning Service Providers (LSPs), necessitating trust among them regarding the safety of their funds in a shared MultiChannel environment.

A key aspect of these constructions is the differentiation in trust dynamics between users and LSPs. Users, represented by Ursula in the discussion, need not trust any individual LSP or a group thereof for the safety of their funds. Conversely, LSPs must place mutual trust in each other to not compromise fund safety, particularly in scenarios involving unilateral exits from the channel. Despite the inherent risk of fund theft by a quorum of LSPs, the system ensures that users' funds remain secure under all circumstances.

To address the trust issue among LSPs without entirely eliminating it, a variant of the MultiChannel based on the Decker-Wattenhofer nested construction is proposed. This method introduces a more secure framework where the necessity for LSPs to trust one another is significantly reduced. The construction employs multiple layers of decrementing-nSequence constructions and unidirectional Spilman channels, creating a complex but secure network of payment channels that safeguard against unauthorized fund access.

One notable drawback of the Spilman unidirectional channels is their handling of failed payments, which complicates the overall channel state and requires periodic cleanup operations to maintain operability. These cleanups, although infrequent, are essential for resetting the channel's state and ensuring ongoing utility. The concept of an Onchain Cleanup is also introduced as a rare but necessary operation to reset the entire system, further emphasizing the intricate balance between usability and security within this framework.

For practical application, the constructions rely heavily on the online presence of both users and LSPs. The design anticipates that while users may be offline frequently, they require immediate service when online. LSPs, conversely, are expected to be continuously online but may occasionally go offline for maintenance or security updates. The MultiChannel construction allows for a seamless user experience even during such downtimes, provided a quorum of LSPs remains operational. This setup reduces the reliance on multiple separate channels, thus economizing on-chain resources and simplifying the user experience.

In summary, the MultiChannel and MultiPTLC constructions represent a significant advancement in the Lightning Network's evolution, addressing critical issues of availability, consistency, and partition tolerance. By carefully balancing trust requirements among users and LSPs and implementing sophisticated channel architectures, these constructions pave the way for a more reliable and user-friendly Lightning Network.