Paper 2024/418

Atomic and Fair Data Exchange via Blockchain

Ertem Nusret Tas, Stanford University
István András Seres, Eötvös Loránd University
Yinuo Zhang, University of California, Berkley
Márk Melczer, Eötvös Loránd University
Mahimna Kelkar, Cornell University and Cornell Tech
Joseph Bonneau, A16Z Crypto Research and New York University
Valeria Nikolaenko, A16Z Crypto Research

We introduce a blockchain Fair Data Exchange (FDE) protocol, enabling a storage server to transfer a data file to a client atomically: the client receives the file if and only if the server receives an agreed-upon payment. We put forth a new definition for a cryptographic scheme that we name verifiable encryption under committed key (VECK), and we propose two instantiations for this scheme. Our protocol relies on a blockchain to enforce the atomicity of the exchange and uses VECK to ensure that the client receives the correct data (matching an agreed-upon commitment) before releasing the payment for the decrypting key. Our protocol is trust-minimized and requires only constant-sized on-chain communication, concretely $3$ signatures, $1$ verification key, and $1$ secret key, with most of the data stored and communicated off-chain. It also supports exchanging only a subset of the data, can amortize the server's work across multiple clients, and offers a general framework to design alternative FDE protocols using different commitment schemes. A prominent application of our protocol is the Danksharding data availability scheme on Ethereum, which commits to data via KZG polynomial commitments. We also provide an open-source implementation for our protocol with both instantiations for VECK, demonstrating our protocol's efficiency and practicality on Ethereum.

Note: L1 CALLDATA cost is fixed in the Introduction.

Available format(s)
Cryptographic protocols
Publication info
Fair Data Exchange (FDE)VECKDanksharding
Contact author(s)
nusret @ stanford edu
seresistvanandras @ gmail com
yinuo yz @ gmail com
melczer7 @ gmail com
mahimna @ cs cornell edu
jbonneau @ gmail com
valeria nikolaenko @ gmail com
2024-03-18: revised
2024-03-09: received
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Creative Commons Attribution


      author = {Ertem Nusret Tas and István András Seres and Yinuo Zhang and Márk Melczer and Mahimna Kelkar and Joseph Bonneau and Valeria Nikolaenko},
      title = {Atomic and Fair Data Exchange via Blockchain},
      howpublished = {Cryptology ePrint Archive, Paper 2024/418},
      year = {2024},
      note = {\url{}},
      url = {}
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