A Flexible Instant Payment System Based on Blockchain

Abstract

Improving the throughput of blockchain systems such as Bitcoin and Ethereum has been an important research problem. Off-chain payments are one of the most promising technologies to tackle this challenge. Once a payment channel, however, is established there exists a strict one-one correspondence between a payee and prepayments, which reduces the flexibility of off-chain payments. In this paper, we propose a flexible instant payment system (FIPS) based on blockchain to improve the flexibility of off-chain payments. In the FIPS system, there exists a depositor who locks enough amounts of tokens on the chain, and supervises payers to make off-chain payments. Therefore, payers can pay to multiple payees off-chain without double-spending. Even the depositor colludes with the payer, and performs double-spending attacks, payees will not suffer any losses as they can withdraw their tokens from the locked tokens of the depositor. Besides, payers can allocate flexibly the prepayments off-chain, and all transactions are settled off-chain. We present a formal generic construction for the FIPS system, prove its security strictly, analyze its related properties, and compare with related schemes in detail. Analyses show that our scheme is flexible and practical.