Paper 2017/684

Z-Channel: Scalable and Efficient Scheme in Zerocash

Yuncong Zhang and Yu Long and Zhen Liu and Zhiqiang Liu and Dawu Gu

Abstract

Decentralized ledger-based cryptocurrencies such as Bitcoin provide a means to construct payment systems without requiring a trusted bank, yet the anonymity of Bitcoin is proved to be far from satisfactory. Zerocash is the first full-fledged anonymous digital currency based on the blockchain technology, using zk-SNARK as the zero-knowledge module for the privacy protection. Zerocash solves the privacy problem but still suffers two major problems: insufficient scalability and latency in making a payment. Meanwhile, micropayment channel proves to be a nice solution to these issues in blockchain-based digital currencies. In this paper, we present Z-Channel, the construction of micropayment system on Zerocash, which effectively solves the scalability and instant payment problems in Zerocash. Z-Channel relies on multisignature and lock time functionalities which are not provided by Zerocash. We manage to improve the Zerocash scheme to support these functionalities without compromising the privacy guaranteed by Zerocash. Finally, the simulation results demonstrate that Z-Channel significantly improves the scalability and reduces the average confirmation time for the payments conducted in Zerocash.