Hashcash

Hashcash is a proof-of-work system designed by Adam Back in the 1990s to prevent denial-of-service attacks. This is done by means of an arithmetic problem that is moderately difficult to set up and calculate, but the solution of which is easy to check.

Applications

Fight against email spam

One use case of Hashcash was to combat the spam problem with technical means. Each e-mail is provided with a header by the sender, which proves that the “virtual postage” has been paid for in the form of a little computing time. The recipient can verify this with comparatively little effort. The basic idea is that perpetrators who want to send many millions of e-mails at very little cost can no longer afford this effort for each individual e-mail.

Today (2019) there are different implementations of Hashcash as free software, e.g. B. as an extension "PennyPost" for Mozilla Thunderbird and in spam filter systems like z. B. SpamAssassin , but activation and configuration is usually optional. Hashcash is therefore not very widespread, partly because other mechanisms of the spam filter systems have been greatly improved.

Bitcoin mining

The Proof of Work concept behind Hashcash is also used, for example, in Bitcoin mining.

Web links

Hashcash Homepage (English)
Hashcash FAQ (English)

Individual evidence

^ Penny Post: What do you mean by Postage Stamp? Retrieved June 10, 2019 .
↑ Penny Post. Retrieved June 10, 2019 (American English).

[1] Penny Post: What do you mean by Postage Stamp? Retrieved June 10, 2019 .

[2] Penny Post. Retrieved June 10, 2019 (American English).