RobustPay+: Robust Payment Routing With Approximation Guarantee in Blockchain-Based Payment Channel Networks

Abstract

The past decade has witnessed an explosive growth in cryptocurrencies, but the blockchain-based cryptocurrencies have also raised many concerns, among which a crucial one is the scalability issue. Suffering from the large overhead of global consensus and security assurance, even the leading cryptocurrencies can only handle up to tens of transactions per second, which largely limits their applications in real-world scenarios. Among many proposals to improve the cryptocurrency scalability, one of the most promising and mature solutions is the payment channel network (PCN), which offers the off-chain settlement of transactions with minimal involvement of expensive blockchain operations. However, transaction failures may occur due to external attacks or unexpected conditions, e.g., an uncooperative user becoming unresponsive. In this paper, we present a distributed robust payment routing protocol RobustPay <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> to resist transaction failures, which achieves robustness, efficiency, distributedness and approximate optimization. Specifically, we investigate the problem of robust routing in PCNs from an optimization perspective, which is to find a pair of payment paths for a payment request, while minimizing the worst-case transaction fee, subject to the timeliness and feasibility constraints. We present a distributed 2-approximation algorithm for this problem. Moreover, we modify the original Hashed Time-lock Contract (HTLC) protocol and adapt it to the robust payment routing protocol to achieve robustness and efficiency. Extensive simulations demonstrate that RobustPay <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> significantly outperforms baseline algorithms in terms of the success ratio and the average accepted value.