Quantum Attacks and Defenses for Proof-of-Stake

Advances in both quantum computation and blockchain systems necessitate a rigid analysis for the security of blockchains in the advent of powerful quantum computers. Computational problems that are proved or believed to be intractable by classical computers are known to be attacked by well-studied quantum algorithms. Such problems are used as basis to secure blockchains and hence the security of such systems must be defended. As proof-of-work is used in early blockchains to maintain consensus, proof-of-stake was proposed to lower its high energy consumption and provide a higher network throughput. Proof-of-Stake has hence got an increasing interest, variations, implementations and enhancements whilst its quantum security defenses remained almost the same. By comparing proof-of-work to proof-of-stake, we find that the latter is more vulnerable to certain attack vectors. We suggest general defenses for quantum-resilient blockchains and thoroughly analyze post-quantum signature schemes to select an appropriate alternative to the most serious threat on conventional digital signatures.