Graphene - efficient interactive set reconciliation applied to blockchain propagation.

We introduce Graphene, a method and protocol for interactive set reconciliation among peers in blockchains and related distributed systems. Through the novel combination of a Bloom filter and an Invertible Bloom Lookup Table (IBLT), Graphene uses a fraction of the network bandwidth used by deployed work for one- and two-way synchronization. We show that, for this specific problem, Graphene is more efficient at reconciling n items than using a Bloom filter at the information theoretic bound. We contribute a fast and implementation-independent algorithm for parameterizing an IBLT so that it is optimally small in size and meets a desired decode rate with arbitrarily high probability. We characterize our performance improvements through analysis, detailed simulation, and deployment results for Bitcoin Cash, a prominent cryptocurrency. Our implementations of Graphene, IBLTs, and our IBLT optimization algorithm are all open-source code.