A Partition Resilient Overlay Network via Blockchain

Blockchains use peer-to-peer networks to handle underlying inter-peer communication, and these networks currently do not have any provable guarantees for desirable properties such as small diameter or partition-resilience. This is not just a theoretical problem: Heilman et al. [1] exploited bugs in bitcoind to isolate a subset of peers in the Bitcoin network by poisoning their address tables. Cryptocurrency blockchains are safety critical systems, so we need principled algorithms to maintain their underlying overlay networks. Our key insight is that we can leverage the blockchain itself to share information among the peers, and thus simplify the overlay maintenance process. We provide communicationefficient protocols to maintain a dynamic hypercubic network for proof-of-work blockchains. Given that the peers have restricted computational resources, and ρ < 0.5 constant fraction of peers are Byzantine, we prove that the network (formed by the honest peers) remains connected for a polynomial number of rounds with high probability, even with polynomial variation in the size of the network. Moreover, these properties hold despite significant churn. A key contribution is a secure mechanism for joining the overlay that relies on the blockchain to help new peers to contact existing members of the overlay. Furthermore, by examining how peers join the system, i.e., the “bootstrapping service”, we give a lower bound showing that (within log factors) our overlay network tolerates the maximum churn rate possible. In fact, we can give a lower bound on churn for any fully distributed service that requires connectivity.