Cryptology ePrint Archive: Report 2018/248

With the present statistical profile of blockchain protocols, the attack can be launched given a few years of prior blockchain operation; hence it is within the realm of feasibility for PoS protocols. Most importantly, it demonstrates how closely transaction fees and rewards are coupled with the security properties of PoS protocols. More broadly, our attack must be reflected and countered in any future PoS design that avoids checkpointing, as well as any effort to remove checkpointing from existing protocols. We describe several mechanisms for protecting against the attack that include context-sensitivity of transactions and chain density statistics.