Paper 2021/1443

Platypus: A Central Bank Digital Currency with Unlinkable Transactions and Privacy Preserving Regulation

Karl Wüst, CISPA Helmholtz Center for Information Security
Kari Kostiainen, ETH Zurich
Noah Delius, ETH Zurich
Srdjan Capkun, ETH Zurich

Due to the popularity of blockchain-based cryptocurrencies, the increasing digitalization of payments, and the constantly reducing role of cash in society, central banks have shown an increased interest in deploying central bank digital currencies (CBDCs) that could serve as a digital cash-equivalent. While most recent research on CBDCs focuses on blockchain technology, it is not clear that this choice of technology provides the optimal solution. In particular, the centralized trust model of a CBDC offers opportunities for different designs. In this paper, we depart from blockchain designs and instead build on ideas from traditional e-cash schemes. We propose a new style of building digital currencies that combines the transaction processing model of e-cash with an account-based fund management model. We argue that such a style of building digital currencies is especially well-suited to CBDCs. We also design the first such digital currency system, called Platypus, that provides strong privacy, high scalability, and expressive but simple regulation, which are all critical features for a CBDC. Platypus achieves these properties by adapting techniques similar to those used in anonymous blockchain cryptocurrencies like Zcash to fit our account model and applying them to the e-cash context.

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Publication info
Published elsewhere. 29th ACM Conference on Computer and Communications Security (CCS) 2022
e-cash privacy regulation CBDC digital currency anonymity compliance zero-knowledge proof
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wuest @ cispa de
2022-09-05: last of 3 revisions
2021-10-27: received
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      author = {Karl Wüst and Kari Kostiainen and Noah Delius and Srdjan Capkun},
      title = {Platypus: A Central Bank Digital Currency with Unlinkable Transactions and Privacy Preserving Regulation},
      howpublished = {Cryptology ePrint Archive, Paper 2021/1443},
      year = {2021},
      doi = {10.1145/3548606.3560617},
      note = {\url{}},
      url = {}
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