Cryptology ePrint Archive: Report 2015/528

SpaceMint: A Cryptocurrency Based on Proofs of Space

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

Abstract: Since its introduction in 2009, Bitcoin has become the most successful cryptocurrency ever deployed. However, the currency's dramatic expansion has also raised serious concerns about its long-term sustainability: (1) Bitcoin mining dynamics have shifted away from decentralization, as dedicated hardware and entry of governments and energy producers has gradually placed most mining power in the hands of a select few, and (2) the network's growth spurt has come with accompanying, vast amounts of energy constantly ``wasted'' solely for the purpose of sustaining the currency.

In this work, we propose SpaceMint, a cryptocurrency based on proofs of space, instead of wasteful proofs of work. Mining in SpaceMint is designed to have low setup and overhead costs, yielding a fairer reward structure for small and large miners. Miners in SpaceMint dedicate disk space rather than computation. In our design, we adapt proof-of-space for the cryptocurrency setting, and propose a new block chain format and transaction types that prevent attacks that exploit the inexpensiveness of mining (from which alternative non-proof-of-work-based proposals have suffered). Our prototype shows that initializing 1TB for mining takes about a day (a one-off cost), and miners on average spend just a fraction of a second per block mined. We also provide a formal game-theoretic analysis modeling SpaceMint as an extensive game, and prove that following the protocol is an equilibrium, thereby arguing for the currency's stability and consensus.

Category / Keywords: cryptocurrency, proofs of space

Date: received 1 Jun 2015, last revised 11 May 2016

Contact author: sunoo at csail mit edu

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Version: 20160512:044404 (All versions of this report)

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