Article: Hashcash - Wikipedia, the free encyclopedia 20120428 15:43:40
Hashcash - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Hashcash
Hashcash is a proof-of-work system designed to limit email spam and denial-of-service attacks. It was proposed in March 1997 by Adam Back.
How it works
Hashcash is a method of adding a textual stamp to the header of an email to prove the sender has expended a modest amount of CPU time calculating the stamp prior to sending the email. In other words, as the sender has taken a certain amount of time to generate the stamp and send the email, it is unlikely that they are a spammer. The receiver can, at negligible computational cost, verify that the stamp is valid. However, the only known way to find a header with the necessary properties is brute force, trying random values until the answer is found; though testing an individual string is easy, if satisfactory answers are rare enough it will require a substantial number of tries to find the answer.
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