Implementing Secure Bridges: Learnings from the Secure Asset Transfer Protocol.

Securely transferring tokenised assets between largely non-interoperable blockchain networks is a great challenge to take on. Implementations must coordinate transactions on multiple blockchain networks which have inherently different characteristics and functionality. Moreover, implementations must coordinate transactions in strict order, in an atomic, synchronised way so that owners do not risk their assets becoming lost, while also mitigating the age-old problem of "avoiding double spend". Several protocols for cross-network asset transfer, i.e. the bridging of assets, exist, and several production bridge implementations exist. However, frequent high-profile security breaches have arguably given bridges a bad reputation. Therefore, there is a clear need for standardised bridge protocols to re-establish trust. One initiative for standardising cross-network bridges is the Secure Asset Transfer Protocol (SATP) developed by the Internet Engineering Task Force (IETF). This protocol establishes four distinctive phases for the asset transfer process, driven by a standardised messaging cycle between specialised bridge orchestration applications, known as gateways. In this paper, we demonstrate a reference framework with functions needed to implement SATP. We describe our implementation of this reference framework, why SATP is unique and why SATP is likely to be an important contribution to powering future bridges.