Hashcash

Hashcash is a proof-of-work system used to limit email spam and denial-of-service attacks. Hashcash was proposed in 1997 by Adam Back[1] and described more formally in Back's 2002 paper "Hashcash – A Denial of Service Counter-Measure".[2] In Hashcash the client has to concatenate a random number with a string several times and hash this new string. It then has to do so over and over until a hash beginning with a certain number of zeros is found.[3]

  1. ^ "A partial hash collision based postage scheme" (Txt). Hashcash.org. Retrieved 13 October 2014.
  2. ^ "Hashcash – A Denial of Service Counter-Measure" (PDF). hashcash.org. 1 August 2002. Retrieved 2 January 2019.
  3. ^ https://www.csc.kth.se/utbildning/kth/kurser/DD143X/dkand12/Group5Mikael/final/Jonatan_Landsberg_and_Anton_Lundqvist.pdf [bare URL PDF]