Aurora: a probabilistic algorithm for distributed ledgers enabling trustless synchronization and transaction inclusion verification

A new node joining a blockchain network first synchronizes with the network to verify ledger state by downloading the entire ledger history. We present Aurora, a probabilistic algorithm that \textit{identifies honest nodes} for transient or persistent communication in the presence of malicious nodes in a blockchain network, or ceases operation if it is unable to do so. The algorithm allows a node joining the network to make an informed decision about its next synchronization step or to verify that a transaction is contained in a valid ledger block without downloading the entire ledger or even the header chain. The algorithm constructs a Directed Acyclic Graph on the network topology to select a subset of nodes including a predefined number of honest nodes with a given probability. It is evaluated on a Bitcoin-like network topology using an open-source blockchain simulator. We investigate algorithm performance and analyze its communication complexity. Our results show that the algorithm facilitates trustless interactions of resource-constrained nodes with a blockchain network containing malicious nodes to enable a leaner initial blockchain download or an efficient and trustless transaction inclusion verification. Moreover, the algorithm can be implemented without any changes to the existing consensus protocol.