Proofs of space Conference Paper


Author(s): Dziembowski, Stefan; Faust, Sebastian; Kolmogorov, Vladimir N; Pietrzak, Krzysztof
Title: Proofs of space
Title Series: LNCS
Affiliation IST Austria
Abstract: Proofs of work (PoW) have been suggested by Dwork and Naor (Crypto’92) as protection to a shared resource. The basic idea is to ask the service requestor to dedicate some non-trivial amount of computational work to every request. The original applications included prevention of spam and protection against denial of service attacks. More recently, PoWs have been used to prevent double spending in the Bitcoin digital currency system. In this work, we put forward an alternative concept for PoWs - so-called proofs of space (PoS), where a service requestor must dedicate a significant amount of disk space as opposed to computation. We construct secure PoS schemes in the random oracle model (with one additional mild assumption required for the proof to go through), using graphs with high “pebbling complexity” and Merkle hash-trees. We discuss some applications, including follow-up work where a decentralized digital currency scheme called Spacecoin is constructed that uses PoS (instead of wasteful PoW like in Bitcoin) to prevent double spending. The main technical contribution of this work is the construction of (directed, loop-free) graphs on N vertices with in-degree O(log logN) such that even if one places Θ(N) pebbles on the nodes of the graph, there’s a constant fraction of nodes that needs Θ(N) steps to be pebbled (where in every step one can put a pebble on a node if all its parents have a pebble).
Keywords: Non-trivial; Technical contribution; Cryptography; Directed graphs; Economics; Electronic money; Alternative concepts; Computational work; Merkle hash tree; Random Oracle model; Service requestors; Shared resources; Denial-of-service attack
Conference Title: CRYPTO: International Cryptology Conference
Volume: 9216
Conference Dates: August 16-20, 2015
Conference Location: Santa Barbara, CA, USA
Publisher: Springer  
Date Published: 2015-08-01
Start Page: 585
End Page: 605
URL:
DOI: 10.1007/978-3-662-48000-7_29
Open access: yes (repository)
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