  Many blockchain consensus protocols have been proposed recently to scale the
throughput of a blockchain with available bandwidth. However, these protocols
are becoming increasingly complex, making it more and more difficult to produce
proofs of their security guarantees. We propose a novel permissionless
blockchain protocol OHIE which explicitly aims for simplicity. OHIE composes as
many parallel instances of Bitcoin's original (and simple) backbone protocol as
needed to achieve excellent throughput. We formally prove the safety and
liveness properties of OHIE. We demonstrate its performance with a prototype
implementation and large-scale experiments with up to 50,000 nodes. In our
experiments, OHIE achieves linear scaling with available bandwidth, providing
about 4-10 Mbps transaction throughput (under 8-20 Mbps per-node available
bandwidth configurations) and at least about 20x better decentralization over
prior works.
