Are Blockchains Decentralized? Unintended Centralities In Distributed Ledgers

Over the past year, Trail of Bits was engaged by the Defense Advanced Research Projects Agency (DARPA) to investigate the extent to which blockchains are truly decentralized. They focused primarily on the two most popular blockchains: Bitcoin and Ethereum. They also investigated proof-of-stake (PoS) blockchains and Byzantine fault tolerant consensus protocols in general. This report provides a high-level summary of results from the academic literature, as well as their novel research on software centrality and the topology of the Bitcoin consensus network.