Search for: All records

In his 2018 paper, Herlihy introduced an atomic protocol for multi-party asset swaps across different blockchains. Practical implementation of this protocol is hampered by its intricacy and computational complexity, as it relies on elaborate smart contracts for asset transfers, and specifying the protocol’s steps on a given digraph requires solving an NP-hard problem of computing longest paths. Herlihy left open the question whether there is a simple and efficient protocol for cross-chain asset swaps in arbitrary digraphs. Addressing this, we study HTLC-based protocols, in which all asset transfers are implemented with standard hashed time-lock smart contracts (HTLCs). Our main contribution is a full characterization of swap digraphs that have such protocols, in terms of so-called reuniclus graphs. We give an atomic HTLC-based protocol for reuniclus graphs. Our protocol is simple and efficient. We then prove that non-reuniclus graphs do not have atomic HTLC-based swap protocols.