MultiChannel and MultiPTLC: Towards A Global High-Availability CP Database For Bitcoin Payments

The discussion revolves around the complexities and innovations within payment protocols, particularly focusing on MultiPTLC (Multi-Part Payment Locked Contracts) versus traditional PTLCs (Payment Locked Contracts) in the context of blockchain and cryptocurrency technologies. A central theme is the necessity for a payment protocol to ensure security and privacy while optimizing for user experience and minimizing the necessity for constant online presence by parties involved in the transaction.

The capability to rollback a MultiPTLC, ensuring the Light Service Providers (LSPs) are the sole entities with knowledge of certain cryptographic keys (receiver-can-claim scalars), hinges on the structure of the MultiPTLC—specifically, it being configured to handle a single unit of payment. This setup contrasts with traditional approaches where multiple units of payment are locked up, necessitating the initiator's continuous online presence to manage payment claims securely. The distinction lies in the ability of MultiPTLCs to significantly reduce the required online time for the initiating party, thanks to a one-time setup that allows LSPs to operate autonomously afterwards.

A notable point of discussion is the risk associated with differentiating deltas (cryptographic elements used in the operation of these contracts) for each participating party. In environments where surveillance by a global observer is possible, using separate deltas can lead to monetary loss if those deltas are intercepted. On the other hand, a well-designed MultiPTLC scheme, even under surveillance, protects against monetary loss, limiting exposure to only privacy risks. This is because, in such a scheme, the initiator locks only a single unit of payment and can safely go offline post-setup, delegating the operational responsibilities to the LSPs.

An innovative proposal highlighted is the reduced necessity for interaction rounds in the proposed MultiPTLC scheme, requiring merely 1.5 roundtrips to establish a set of receiver-can-claim points plus tweaks, which are cryptographic measures to secure the transaction. This system allows for a streamlined process where LSPs can autonomously manage payment retries without further input from the initiating party, based on a trust model among the LSPs themselves. The described mechanism contrasts sharply with current protocols that require extensive back-and-forth communication per payment attempt, illustrating a significant efficiency gain and enhanced user experience.

Moreover, this approach introduces a more flexible and user-friendly payment protocol, allowing for multiple payment attempts under a single "payment plan" without necessitating additional interactions from the payment initiator. It emphasizes a design philosophy where end-user security and experience are both prioritized, marking a departure from conventional trade-offs between usability and security often seen in digital payment systems. This MultiPTLC method also highlights an advancement in how LSPs operate, enabling them to conduct multiple payment attempts on behalf of the initiator without requiring detailed knowledge of the recipient or the intricacies of the payment path, thus simplifying the transaction process and enhancing the potential for successful payments in the network.