Hashcash is a proof-of-work system designed to limit email spam and denial-of-service attacks. It was created by Adam Back in 1997. The idea behind Hashcash is to require the sender of an email to perform a computational task, which involves calculating a hash that meets certain criteria. This process takes time and computational resources, making it more expensive for spammers to send large volumes of emails.
New to topics? Read the docs here!