Rapidash: Atomic Swaps Secure under User-Miner Collusion

Hao Chung; Elisaweta Masserova; Elaine Shi; Sri AravindaKrishnan Thyagarajan

Paper 2022/1063

Rapidash: Atomic Swaps Secure under User-Miner Collusion

Hao Chung, Carnegie Mellon University

Elisaweta Masserova, Carnegie Mellon University

Elaine Shi, Carnegie Mellon University

Sri AravindaKrishnan Thyagarajan, University of Sydney

Abstract

Cross-chain trading is fundamental to blockchains and Decentralized Finance (DeFi). A way to achieve such trading in a truly decentralized manner, i.e., without trusted third parties, is by using atomic swaps. However, recent works revealed that Hashed Time-Lock Contract, a key building block of the existing atomic swaps, is entirely insecure in the presence of user-miner collusion. Specifically, a user can bribe the miners of the blockchain to help it cheat. In this work, we give the first and rigorous formal treatment of fair trading on blockchains, where users and miners may enter arbitrary binding contracts on the side. We propose Rapidash, a new atomic swap protocol, and prove its incentive-compatibility in the presence of user-miner collusion. Specifically, we show that Rapidash satisfies a coalition-resistant Nash equilibrium absent external incentives. We give instantiations of Rapidash that are compatible with Bitcoin and Ethereum, and incur only minimal overheads in terms of costs for the users.

Note: Previous versions of the paper included the notion of bounded maximin fairness, which is now exclusively available in https://eprint.iacr.org/2025/1086. Together, both papers subsume Ponyta (https://eprint.iacr.org/2022/582).

Metadata

Available format(s): PDF
Category: Cryptographic protocols
Publication info: Published elsewhere. Financial Cryptography and Data Security 2025
Keywords: blockchain fair exchange side-contract-resilient atomic swap
Contact author(s): chunghaoqc @ gmail com
elisawem @ andrew cmu edu
elainershi @ gmail com
aravind thyagarajan @ sydney edu au
History: 2025-06-26: last of 5 revisions; 2022-08-16: received; See all versions
Short URL: https://ia.cr/2022/1063
License: CC BY

BibTeX

@misc{cryptoeprint:2022/1063,
      author = {Hao Chung and Elisaweta Masserova and Elaine Shi and Sri AravindaKrishnan Thyagarajan},
      title = {Rapidash: Atomic Swaps Secure under User-Miner Collusion},
      howpublished = {Cryptology {ePrint} Archive, Paper 2022/1063},
      year = {2022},
      url = {https://eprint.iacr.org/2022/1063}
}