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Proofs of Space

  • Stefan DziembowskiEmail author
  • Sebastian Faust
  • Vladimir Kolmogorov
  • Krzysztof Pietrzak
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 9216)

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 \(O(\log \log N)\) such that even if one places \(\varTheta (N)\) pebbles on the nodes of the graph, there’s a constant fraction of nodes that needs \(\varTheta (N)\) steps to be pebbled (where in every step one can put a pebble on a node if all its parents have a pebble).

Keywords

Hash Function Proof System Random Oracle Execution Phase Random Oracle Model 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© International Association for Cryptologic Research 2015

Authors and Affiliations

  • Stefan Dziembowski
    • 1
    Email author
  • Sebastian Faust
    • 2
  • Vladimir Kolmogorov
    • 3
  • Krzysztof Pietrzak
    • 3
  1. 1.University of WarsawWarszawaPoland
  2. 2.Ruhr-University BochumBochumGermany
  3. 3.IST AustriaKlosterneuburgAustria

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