Formalising a Gateway-based Blockchain Interoperability Solution with Event-B

In recent years, multiple solutions have been proposed for blockchain interoperability. However, designing these solutions is complex, and design failures have caused great economic damage to their owners. Safety and liveness are essential properties for these solutions, and formalisation eases their verification. However, only a few efforts were performed to formalise interoperability solutions with known formal methods. TLA+ and PAT were previously used; however, the Event-B method has not been explored, although it might be a suitable approach. The purpose of this paper was to explore the formalisation of a gateway-based interoperability solution with Event-B. The results showed that the method was suitable and that a straightforward specification could be developed considering Ethereum and Hyperledger Fabric as the involved blockchains. The specification was assessed with three strategies that enabled its verification and validation. In particular, formal verification (e.g. safety properties), functional validation, and functional utility. These promising results constitute a step forward in the development of formal specifications for blockchain interoperability solutions.