Security Attacks on Multi-Stage Proof-of-Work

Multi-stage Proof-of-Work is a recently proposed protocol which extends the Proof-of-Work protocol used in Bitcoin. It splits Proof-of-Work into multiple stages, to achieve a more efficient block generation and a fair reward distribution.In this paper we study some of the Multi-stage Proof-of-Work security vulnerabilities. Precisely, we present two attacks: a Selfish Mining attack and a Selfish Stage-Withholding attack. We show that Multi-stage Proof-of-Work is not secure against a selfish miner owning more than 25% of the network hashing power. Moreover, we show that Selfish Stage-Withholding is a complementary strategy to boost a selfish miner's profitability.