ZK-gossip for lightning channel announcements

This method cleverly dissociates channel ownership from on-chain outputs by employing ZK-proofs, thereby allowing participants to prove control over a Unspent Transaction Output (UTXO) without revealing its specific outpoint. The introduction of a new message type, channel_announcement_2, which incorporates a Musig2 signature as part of this proof mechanism, underscores the technical sophistication and privacy-centric focus of the proposal.

Central to this approach is the reliance on Utreexo accumulators for validating the inclusion of a channel output without directly linking it to its on-chain presence. By extracting essential data from existing channel announcements and combining them with Utreexo proofs, the system can verify key elements such as bitcoin keys, node IDs, and channel capacities securely and anonymously. This verification process is encapsulated in the proposed channel_announcement_zk message format, which integrates these elements into a cohesive structure that supports efficient validation by network nodes.

One of the notable challenges addressed by this proposal is the need for channels to periodically confirm their operational status within the network. Due to the indirect nature of ZK-proofs in verifying channel closings, the suggestion for channels to refresh their announcements every two weeks offers a practical solution to maintaining an accurate and current view of the network's topology. This periodic confirmation serves as a form of heartbeat, ensuring that only active channels are considered in routing decisions, thus enhancing both privacy and network efficiency.

The detailed documentation and code provided in the associated branch demonstrate the feasibility of this approach, leveraging RiscZero for integrating additional constraints into the UTXO verification process. This work not only showcases the technical viability of the proposed system but also invites further examination and feedback from the community. It represents a thoughtful exploration into balancing the twin goals of privacy preservation and security within the LN ecosystem, potentially setting a new standard for future developments in blockchain privacy technologies.