Paper 2026/904
Sponsored Fair Exchange (Extended Abstract)
, École Polytechnique Fédérale de LausanneAbstract
We propose a costless platform for fair exchange based on smart contracts to favor economic inclusion. Our smart contract is minimal, as most of communication is done offchain. The smart contract costs are covered by incentivized sponsors. Our protocol is a knowledge-coin exchange: it allows to exchange a digital item, characterized by an automatically verifiable description, against a payment in cryptocurrency. The exchange is fair in the sense that either both parties receive what they expect (the exchange completes) or both parties lose nothing (the exchange is canceled). We ensure a costless transaction in cancelation cases, and a transaction with pre-determined fee if it completes. We also ensure privacy of the transaction. Our protocol offers an improvement compared to OptiSwap: we can work with any description function. The complexity is never higher and sometimes significantly smaller. Namely, the worst case complexity is logarithmic instead of being linear. Furthermore, we introduce sponsoring as an enabler for economic inclusion.
Note: Presented at the Workshop on Cryptographic Tools for Blockchains (CTB) 2026 - affiliated with EUROCRYPT 2026.
Metadata
- Available format(s)
-
PDF
- Category
- Cryptographic protocols
- Publication info
- Preprint.
- Keywords
- fair exchangeblockchain
- Contact author(s)
- serge vaudenay @ epfl ch
- History
- 2026-05-10: approved
- 2026-05-08: received
- See all versions
- Short URL
- https://ia.cr/2026/904
- License
-
CC BY
BibTeX
@misc{cryptoeprint:2026/904,
author = {Serge Vaudenay},
title = {Sponsored Fair Exchange (Extended Abstract)},
howpublished = {Cryptology {ePrint} Archive, Paper 2026/904},
year = {2026},
url = {https://eprint.iacr.org/2026/904}
}
