Cross-Chain Atomic Swaps without Time Locks

Since the introduction of the blockchain technology in the form of the Bitcoin [1] cryptocurrency, numerous blockchains have been introduced with applications beyond cryptocurrency. Introduction of smart contracts and tokenization of assets has made blockchain technology a decentralized, replicated and transparent program execution engine with the capability to represent real-world assets as tokens. However, with the diversity of blockchain platforms, and diversity of applications, interoperability between applications has become an important problem. Especially with the increasing use of asset tokenizations, cross-chain token transfer which guarantees safety and live-ness properties became necessary. Atomic cross chain transactions are building blocks for the cross chain execution of the smart contract. Atomic cross-chain swap is the simplest kind of the cross chain transaction. In this paper we present a novel atomic cross chain swap protocol. Our protocol does not use time locks unlike previously proposed solutions. Time-locking leaves the funds locked at the whim of the proposer, and hash-time locking protocol is probabilistic, in the sense that there is a possibility that proposer might not complete the transaction and cheat the other party. Our protocol is deterministic and ends in a finite number of steps. We also provide formal proofs of safety and liveness properties of our protocol.