Z-Channel: Scalable and Efficient Scheme in Zerocash

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 enough. Zerocash is the first full-fledged anonymouse digital currency based on the blockchain technology, using zk-SNARK as the zero-knowledge module for the privacy preserving. Zerocash solves the privacy problem but also brings some other issues, including insufficient scalability as in Bitcoin. Meanwhile, Lightning network proves to be a nice solution to solve the scalability problem in Bitcoin. However, to employ the idea of lightning network in Zerocash is a great challenge due to the lack of programmability of Zerocash. We modify the Zerocash scheme to implement multisignature scheme and the lock time mechanism without compromising the privacy guarantee provided by Zerocash. With these two mechanisms, we present the construction of micropayment system Z-Channel on the basis of Zerocash. The Z-Channel system effectively solves the scalability and instant payment problems in Zerocash.