International Association
for Cryptologic Research

With the growing number of decentralized finance applications, transaction fairness in blockchains has gained intensive research interest. As a broad concept in the distributed systems and blockchain literature, fairness has been used in different contexts, varying from ones related to the system's liveness to ones that focus on the received order of transactions. In this work, we revisit the fairness definitions known so far and provide a more generic fairness definition called verifiable fairness. Our definition relaxes the ordering rules that are inherently embedded in prior definitions to a predicate defined by concrete applications. Our notion thus gains flexibility and generality, capturing all existing fairness definitions. We provide a solution that achieves our new fairness definition, leveraging trusted hardware. Unlike prior works that usually design a dedicated consensus protocol to achieve fairness goals, our solution is modular and can be integrated with any blockchain system. We implement a prototype using Go Ethereum (Geth) as the blockchain and OpenSGX as the trusted hardware. Evaluation results reveal that our construction imposes only minimal overhead on existing blockchain systems.