Atomic Commitment Across Blockchains
It addresses the need for secure peer-to-peer asset exchanges across blockchains without centralized intermediaries, which is crucial for users in decentralized finance, but is incremental as it builds on existing cross-chain swap protocols.
The paper tackles the problem of ensuring all-or-nothing atomicity in cross-chain transactions, where current protocols fail in asynchronous environments due to crash failures or network delays, and presents AC3WN, a decentralized protocol that guarantees either all smart contracts are redeemed or all are refunded.
The recent adoption of blockchain technologies and open permissionless networks suggest the importance of peer-to-peer atomic cross-chain transaction protocols. Users should be able to atomically exchange tokens and assets without depending on centralized intermediaries such as exchanges. Recent peer-to-peer atomic cross-chain swap protocols use hashlocks and timelocks to ensure that participants comply to the protocol. However, an expired timelock could lead to a violation of the all-or-nothing atomicity property. An honest participant who fails to execute a smart contract on time due to a crash failure or network delays at her site might end up losing her assets. Although a crashed participant is the only participant who ends up worse off, current proposals are unsuitable for atomic cross-chain transactions in asynchronous environments where crash failures and network delays are the norm. In this paper, we present AC3WN, the first decentralized all-or-nothing atomic cross-chain commitment protocol. The redeem and refund events of the smart contracts that exchange assets are modeled as conflicting events. An open permissionless network of witnesses is used to guarantee that conflicting events could never simultaneously occur and either all smart contracts in an atomic cross-chain transaction are redeemed or all of them are refunded.