Cryptology ePrint Archive: Report 2020/560

ZeroJoin: Combining ZeroCoin and CoinJoin

Alexander Chepurnoy and Amitabh Saxena

Abstract: We present ZeroJoin, a practical privacy-enhancing protocol for blockchain transactions. ZeroJoin can be considered a combination of ZeroCoin and CoinJoin. It borrows ideas from both but attempts to overcome some of their drawbacks. Like ZeroCoin, our protocol uses zero-knowledge proofs and a pool of participants. However, unlike ZeroCoin, our proofs are very efficient, and our pool size is not monotonically increasing. Thus, our protocol overcomes the two major drawbacks of ZeroCoin. Our approach can also be considered a non-interactive variant of CoinJoin, where the interaction is replaced by a public transaction on the blockchain. The security of ZeroJoin is based on the Decision Diffie-Hellman (DDH) assumption. We also present ErgoMix, a practical implementation of ZeroJoin on top of Ergo, a smart contract platform based on Sigma protocols. While ZeroJoin contains the key ideas, it leaves open the practical issue of handling fees. The key contribution of ErgoMix is a novel approach to handle fee in ZeroJoin.

Category / Keywords: cryptographic protocols / cryptocurrency, privacy, DDH, zero knowledge

Date: received 13 May 2020, last revised 4 Jun 2020

Contact author: kushti at protonmail ch

Available format(s): PDF | BibTeX Citation

Version: 20200604:152748 (All versions of this report)

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