The proof of work mechanism by which many blockchain-based protocols achieve consensus may be undermined by the use of quantum computing in mining—even when all cryptographic primitives are replaced with post-quantum secure alternatives. First, we offer an impossibility result: we prove that quantum (Grover) speedups in solving a large, natural class of proof-of-work puzzles cause an inevitable incentive incompatibility in mining, by distorting the reward structure of mining in proof-of-work-based protocols such as Bitcoin. We refer to such distortion as the Superlinearity Problem. Our impossibility result suggests that for robust post-quantum proof-of-work-based consensus, we may need to look beyond standard cryptographic models. We thus propose a proof-of-work design in a random-beacon model, which is tailored to bypass the earlier impossibility. We conclude with a discussion of open problems, and of the challenges of integrating our new proof-of-work scheme into decentralised consensus protocols under realistic conditions.
CITATION STYLE
Park, S., & Spooner, N. (2024). The Superlinearity Problem in Post-quantum Blockchains. In Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) (Vol. 13950, pp. 200–217). Springer Science and Business Media Deutschland GmbH. https://doi.org/10.1007/978-3-031-47754-6_12
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