Paper 2020/560

Zerojoin: Combining Zerocoin and CoinJoin

Alexander Chepurnoy and Amitabh Saxena


We present Zerojoin, a privacy-enhancing protocol for UTXO blockchains. Like Zerocoin, our protocol uses zero-knowledge proofs and a pool of participants. However, unlike Zerocoin, our pool size is not monotonically increasing. Thus, our protocol overcomes the major drawback 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 relies on the Decisional-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 fees in Zerojoin.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. Minor revision. Data Privacy Management, Cryptocurrencies and Blockchain Technology. DPM 2020, CBT 2020.
cryptocurrencyprivacyDDHzero knowledge
Contact author(s)
kushti @ protonmail ch
2021-08-29: last of 4 revisions
2020-05-15: received
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      author = {Alexander Chepurnoy and Amitabh Saxena},
      title = {Zerojoin: Combining Zerocoin and {CoinJoin}},
      howpublished = {Cryptology ePrint Archive, Paper 2020/560},
      year = {2020},
      note = {\url{}},
      url = {}
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