Erlay : efficient transaction relay in Bitcoin

Abstract

Bitcoin is a top-ranked cryptocurrency that has experienced huge growth and survived numerous attacks. The protocols making up Bitcoin must therefore accommodate the growth of the network and ensure security. However, Bitcoin’s transaction dissemination protocol has mostly evaded optimization. This protocol is based on flooding and though it is secure and fault-tolerant, it is also highly inefficient. Specifically, our measurements indicate that 43% of the traffic generated by transaction dissemination in the Bitcoin network is redundant. In this paper we introduce a new transaction dissemination protocol called Erlay. Erlay is a hybrid protocol that combines limited flooding with intermittent reconciliation. We evaluated Erlay in simulation and by implementing and deploying it at scale. Compared to Bitcoin’s current protocols, Erlay reduces the bandwidth used to announce transactions by 84% without significantly affecting privacy or propagation speed. In addition, Erlay retains the existing Bitcoin security guarantees and is more scalable relative to the number of nodes in the network and their connectivity. Erlay is currently being investigated by the Bitcoin community for future use with the Bitcoin protocol.