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.
Read more https://packetstormsecurity.com/files/167566/Are_Blockchains_Decentralized.pdf