CNS Core: Small: Network Architecture and Routing Protocols for Payment Channel Networks

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Blockchain technology is attracting considerable interest for its potential to enable new decentralized, secure applications such as payment systems. However, current blockchain systems suffer from severe scalability limitations. For example, blockchain-based digital currencies have orders of magnitude worse transaction throughput and confirmation latency than the established payment systems we use in our daily lives. This project proposes to tackle this fundamental scalability challenge by investigating so-called "payment channel networks". A payment channel network enables participants to transfer funds securely through a set of intermediaries, without recording every transaction on a public ledger (the blockchain). This project starts with the observation that payment channel networks have similarities to data communication networks (and also important differences), but their designs are primitive by comparison. The goal this research is to develop network protocols for payment channel networks --- protocols that are tailor-made for these networks while being deeply rooted in decades of research on data networks. If successful, this project would enable principled, efficient, and cost-effective approaches to building decentralized payment systems and improving the scalability of many blockchain systems. A central challenge for a payment channel network is how to route payments across the network efficiently. Routing payments is non-trivial since it requires finding paths with sufficient funds and keeping payment channel funds balanced. Payment channels used more frequently in one direction eventually run out of funds in that direction blocking further transactions through them. Inefficient routing limits network throughput and increases transaction costs, as it forces routers to deposit a large amount of funds into their payment channels up front, or pay high transaction fees to repeatedly rebalance payment channels on the blockchain. This research seeks to develop a new payment channel network that achieves high transaction throughput at low cost. To this end, the researchers plan to (1) develop a packet-switched payment channel network architecture, (2) invent imbalance-aware routing and rate control algorithms with theoretical guarantees, and (3) investigate privacy and incentive-compatibility of payment channel network protocols.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.