Paper 2019/1265

WaterCarver: Anonymous Confidential Blockchain System based on Account Model

Jiajun Xin, Pei Huang, Lei Chen, Xin Lai, Xiao Zhang, Wulu Li, and Yongcan Wang

Abstract

The Account-model-based blockchain system gains its popularity due to its ease of use and native support of smart contracts. However, the privacy of users now becomes a major concern and bottleneck of its further adoption because users are not willing to leaving permanent public records online. Conventionally, the privacy of users includes transaction confidentiality and anonymity. While confidentiality can be easily protected using confidential transaction technique, anonymity can be quite challenging in an account-model-based blockchain system, because every transaction in the system inevitably updates transaction sender's as well as receiver's account balance. Even when the privacy of a blockchain system is well-protected, however, regulation becomes a new challenge to counter for further adoption of this system. In this paper, we introduce a novel transaction-mix protocol, which provides confidentiality and, moreover, anonymity to account-model-based blockchain systems. By leveraging the state of art verifiable shuffle scheme to construct a shuffle of confidential transactions, we build one practical anonymous confidential blockchain system, WaterCarver, upon account model with the help of confidential transactions, verifiable shuffle, and zero-knowledge proofs. We further provide an efficient and robust solution for dynamic regulation with multiple regulators. Our regulation method achieves flexibility and perfect forward secrecy. Experiments show that the overall Transactions Per Second (TPS) of our system can be as large as 600 on a simple desktop.