Cryptology ePrint Archive: Report 2015/528

SpaceMint: A Cryptocurrency Based on Proofs of Space

Sunoo Park and Albert Kwon and Georg Fuchsbauer and Peter Gai and Jol Alwen and Krzysztof Pietrzak

Abstract: Bitcoin has become the most successful cryptocurrency ever deployed, and its most distinctive feature is that it is decentralized. Its underlying protocol (Nakamoto consensus) achieves this by using proof of work, which has the drawback that it causes the consumption of vast amounts of energy to maintain the ledger. Moreover, Bitcoin mining dynamics have become less distributed over time.

Towards addressing these issues, we propose SpaceMint, a cryptocurrency based on proofs of space instead of proofs of work. Miners in SpaceMint dedicate disk space rather than computation. We argue that SpaceMint's design solves or alleviates several of Bitcoin's issues: most notably, its large energy consumption. SpaceMint also rewards smaller miners fairly according to their contribution to the network, thus incentivizing more distributed participation.

This paper adapts proof of space to enable its use in cryptocurrency, studies the attacks that can arise against a Bitcoin-like blockchain that uses proof of space, and proposes a new blockchain format and transaction types to address these attacks. Our prototype shows that initializing 1 TB for mining takes about a day (a one-off setup cost), and miners spend on average just a fraction of a second per block mined. Finally, we provide a game-theoretic analysis modeling SpaceMint as an extensive game (the canonical game-theoretic notion for games that take place over time) and show that this stylized game satisfies a strong equilibrium notion, thereby arguing for SpaceMint's stability and consensus.

Category / Keywords: cryptocurrency, proofs of space

Original Publication (with major differences): Financial Crypto 2018

Date: received 1 Jun 2015, last revised 28 Feb 2018

Contact author: sunoo at csail mit edu

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Version: 20180301:065854 (All versions of this report)

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