Paper 2024/246

OCash: Fully Anonymous Payments between Blockchain Light Clients

Adam Blatchley Hansen, Aarhus University
Jesper Buus Nielsen, Aarhus University
Mark Simkin, Flashbots
Abstract

We study blockchain-based provably anonymous payment systems between light clients. Such clients interact with the blockchain through full nodes, which can see what the light clients read and write. The goal of our work is to enable light clients to perform anonymous payments, while maintaining privacy even against the full nodes through which they interact with the blockchain. We formalize the problem in the UC model and present a provably secure solution. We show that a variation of tree ORAM gives obliviousness even when an adversary can follow how its own data elements move in the tree. We use this for anonymity via shuffling of payments on the blockchain, while at the same time allowing the light client to know a few positions among which to find its payment without knowing the current state of the blockchain. In comparison to existing works, we are the first ones that simultaneously provide strong anonymity guarantees, provable security, and anonymity with respect to full nodes. Along the way, we make several contributions that may be of independent interest. We define and construct anonymous-coin friendly encryption schemes and show how they can be used within anonymous payment systems. We define and construct efficient compressible randomness beacons, which produce unpredictable values in regular intervals and allow for storing all published values in a short digest.

Metadata
Available format(s)
PDF
Category
Cryptographic protocols
Publication info
A major revision of an IACR publication in PKC 2025
Keywords
AnonymityeCashblockchain
Contact author(s)
blatchley @ cs au dk
jbn @ cs au dk
mark @ univariate org
History
2025-02-26: revised
2024-02-15: received
See all versions
Short URL
https://ia.cr/2024/246
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2024/246,
      author = {Adam Blatchley Hansen and Jesper Buus Nielsen and Mark Simkin},
      title = {{OCash}: Fully Anonymous Payments between Blockchain Light Clients},
      howpublished = {Cryptology {ePrint} Archive, Paper 2024/246},
      year = {2024},
      url = {https://eprint.iacr.org/2024/246}
}
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