Fulgor: Concurrent and Privacy Preserving Transactions with Payment-Channel Networks [29E-35E]
Giulio Malavolta, Pedro Moreno-Sanchez, Aniket Kate, Matteo Maffei, Srivatsan Ravi
Blockchain payment protocols based on global consensus such as Bitcoin are inherently limited in transaction throughput and latency. Current efforts to address this key issue focus on off-chain payment channels that can be combined in a Payment-Channel Network (PCN) that enables an unlimited number of payments and requires access to the blockchain only to register the initial and final capacity of each channel. While this approach paves the way for low latency and high throughput of payments, its deployment in practice raises several privacy issues, which have been understudied so far. In this work, we lay the foundations for privacy in PCN, presenting a definitional framework as well as a practical and provably secure enforcement solution. In particular, we present Fulgor, the first payment protocol for PCNs that provides provable privacy guarantees. We have implemented Fulgor and showed that it allows privacy preserving payments in less than 1 second, thereby demonstrating its feasibility in practice. Finally, we formally study for the first time how to handle concurrent payments in a non-blocking manner while maintaining the decentralized nature of PCNs.