Fee-Based Spam Prevention For Lightning

The correspondence discusses enhancements and potential issues in the implementation of a new protocol within the context of Lightning Network transactions. Initially, it acknowledges a solution that addresses an immediate problem but also introduces a significant increase in link-layer latency. The proposal includes simplifying the process by excluding update_add_htlc messages and assuming symmetric commitment transactions. This streamlined approach is illustrated through a step-by-step explanation where Alice and Bob exchange signatures and revocation secrets for new and previous commitment transactions, respectively. This method not only simplifies the transaction process but also highlights an advantage of the current commitment protocol: it reduces the time required for forwarding the Hash Time-Locked Contract (HTLC) to the next hop, achieving a best-case forwarding time of n*0.5 round-trip time (RTT) across an n-hop payment.

Further examination of the proposed protocol reveals an increase in the full resolution time to 2.5 RTT from the initial 1.5 RTT, potentially tripling the slow down in payment processing as perceived by the final receiver. While the sender observes a twofold increase in delay, this adjustment underscores a critical expansion in the operational timeframe required for completing transactions. Despite these concerns, the discussion shifts to acknowledge the merits of hold fees within Modified Adjusted Duration (MAD)-based Optimistic Payment Routing (OPR)-style protocols. Although initially considered for spam mitigation, the concept of hold fees extends to encompass the broader application of not-immediately-settled payments. This notion suggests a paradigm where payments are delayed, yet forwarding nodes receive fair compensation for their part in the delayed transmission. The idea of not immediately settling payments, which could cater to a significant demand, is further explored with reference to hold invoices, advocating for its adoption provided it ensures equitable remuneration for the nodes involved in the payment forwarding process.