Paper 2020/543

Kachina - Foundations of Private Smart Contracts

Thomas Kerber, Aggelos Kiayias, and Markulf Kohlweiss


Smart contracts present a uniform approach for deploying distributed computation and have become a popular means to develop security critical applications. A major barrier to adoption for many applications is the public nature of existing systems, such as Ethereum. Several systems satisfying various definitions of privacy and requiring various trust assumptions have been proposed; however, none achieved the universality and uniformity that Ethereum achieved for non-private contracts: One unified method to construct most contracts. We provide a unified security model for private smart contracts which is based on the Universal Composition (UC) model and propose a novel core protocol, Kachina, for deploying privacy-preserving smart contracts, which encompasses previous systems. We demonstrate the Kachina method of smart contract development, using it to construct a contract that implements privacy-preserving payments, along the lines of Zerocash, which is provably secure in the UC setting and facilitates concurrency.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. Major revision. 2021 IEEE Computer Security Foundations Symposium
blockchainsmart contractsprivacyzero-knowledge
Contact author(s)
papers @ tkerber org
2021-07-16: last of 3 revisions
2020-05-15: received
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      author = {Thomas Kerber and Aggelos Kiayias and Markulf Kohlweiss},
      title = {Kachina - Foundations of Private Smart Contracts},
      howpublished = {Cryptology ePrint Archive, Paper 2020/543},
      year = {2020},
      note = {\url{}},
      url = {}
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