  We introduce Casper, a proof of stake-based finality system which overlays an
existing proof of work blockchain. Casper is a partial consensus mechanism
combining proof of stake algorithm research and Byzantine fault tolerant
consensus theory. We introduce our system, prove some desirable features, and
show defenses against long range revisions and catastrophic crashes. The Casper
overlay provides almost any proof of work chain with additional protections
against block reversions.
