On August 1, 2002, Adam Back officially presented the Hashcash paper, a precursor to the system used in Bitcoin mining.

https://m.stacker.news/42838

In 1997, Adam Back, a British cryptographer and cypherpunk, proposed Hashcash, a mechanism designed to combat email spam and denial-of-service (DoS) attacks. It was a proof-of-work algorithm that required a certain amount of computational work to send an email, making spam sending uneconomical.

Five years later, on August 1, 2002, Back more formally described the functioning of Hashcash in the paper “Hashcash – A Denial of Service Counter-Measure,” which would later be cited in the Bitcoin white paper.

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