2-hop Blockchain: Combining Proof-of-Work and Proof-of-Stake Securely

Bitcoin-like blockchains use a proof-of-work (PoW) mechanism, where security holds if the majority of the computing power is under the control of honest players. However, this assumption has been seriously challenged recently, and Bitcoin-like systems fail if this assumption is violated. In this work we propose a novel 2-hop blockchain protocol that combines PoW and proof-of-stake (PoS) mechanisms. Our analysis shows that the protocol is secure as long as the honest players control a majority of the collective resources (which consist of both computing power and stake). In particular, even if the adversary controls more than 50% of the computing power, security still holds if the honest parties hold sufficiently high stake in the system. As an added contribution, our protocol also remains secure against adaptive adversaries.

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