Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Hashcash
open-in-new
<p>Hashcash is a <a href="/facts/Proof-of-work_system/GKI1LcQU">proof-of-work system</a> used to limit <a href="/facts/Email_spam/ARJr6Aem">email spam</a> and <a href="/facts/Denial-of-service_attack/6nkoK02J">denial-of-service attacks</a>. Hashcash was proposed in 1997 by <a href="/facts/Adam_Back/Gmhb1IQn">Adam Back</a> and described more formally in Back's 2002 paper "Hashcash – A Denial of Service Counter-Measure". 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. </p>