Privacy-Utility Tradeoffs in Routing Cryptocurrency over Payment Channel Networks

摘要

As the adoption of cryptocurrencies grows to unprecedented levels, the scalability of blockchain technologies has become increasingly important. A major open question is whether cryptocurrencies are fundamentally able to support as much traffic as traditional, centralized solutions. One prominent approach for improving the scalability of blockchains is payment channel networks (PCNs) [1]. Instead of committing every transaction to the blockchain, a separate overlay network (called a PCN) is maintained. Each node represents a user, and each edge (or payment channel) represents pre-allocated funds that can be efficiently transacted between the two endpoints under a mutual agreement. Users can transact with each other by relaying payments over a sequence of channels.A major challenge in deploying PCNs in real-world cryptocurrencies is the tension between throughput and privacy. Each time a user wishes to route a transaction, it must find a path through the PCN with enough pre-allocated funds to support the transaction. However, in today's PCNs, edge balances are not publicly revealed for privacy reasons. This causes failed routing attempts, thereby decreasing the transaction throughput of the system and ultimately hindering scalability. The goal of this paper is to quantify this tradeoff between privacy and utility in PCNs.