International Association
for Cryptologic Research

We propose a decentralized cryptocurrency called Spacemint, which is based on a block chain

ledger similar to that of Bitcoin, but where the wasteful proofs of

work are replaced by efficient \\emph{proofs of space}, recently introduced by

Dziembowski et al. Instead of requiring that a majority of the network\'s

computing power is controlled by honest miners (as in Bitcoin), our

currency requires that honest miners dedicate more net disk space than a

potential adversary.

In Spacemint, once a miner has dedicated and initialized some space,

participating in the mining process is very cheap. A new block is

added to the chain every fixed period of time, and in every period a

miner just has to make a small number of lookups to the stored space

to check if she ``wins\", and thus can efficiently add the next block

to the chain and get the mining reward. In this paper, we detail the

construction of Spacemint, analyze its security and

game-theoretic properties, and study its performance.

Our prototype shows that it takes approximately 25 seconds to prove

over a terabyte of space, and it takes a fraction of a second to verify the proof.