Blockchain Gateways, Bridges and Delegated Hash-Locks

In the current work we discuss the notion of gateways as a means for interoperability across different blockchain systems. We discuss two key principles for the design of gateway nodes and scalable gateway protocols, namely (i) the opaque ledgers principle as the analogue of the autonomous systems principle in IP datagram routing, and (ii) the externalization of value principle as the analogue of the end-to-end principle in the Internet architecture. We illustrate the need for a standard gateway protocol by describing a unidirectional asset movement protocol between two peer gateways, under the strict condition of both blockchains being private/permissioned with their ledgers inaccessible to external entities. Several aspects of gateways and the gateway protocol is discussed, including gateway identities, gateway certificates and certificate hierarchies, passive locking transactions by gateways, and the potential use of delegated hash-locks to expand the functionality of gateways.