[ANNOUNCE] hash cash postage implementation
The date is March 28, 1997, when the 2,000-or-so subscribers of the Cypherpunks mailing list receive an email[1] with the above header in their inbox. The sender is a 26-year-old British postdoc at the University of Exeter, a young cryptographer and prolific contributor to the mailing list named Dr. Adam Back. The email includes a description and early implementation of what he describes as a “partial hash collision based postage scheme” — a sort of stamp equivalent for emails, based on a nifty cryptographic trick.
“The idea of using partial hashes is that they can be made arbitrarily expensive to compute,” wrote Back, explaining the advantage of his system, “and yet can be verified instantly.”
This proposal by the cryptographer who would go on to become the current Blockstream[2] CEO did not immediately garner much attention on the email list; just one reader responded[3], with a technical inquiry about the hashing algorithm of choice. Yet, the technology underlying Hashcash — proof of work — would shape research into digital money for more than a decade to come.
“Pricing via Processing or Combatting Junk Mail”
Back’s Hashcash was actually not the first solution of its kind.
By the early 1990s, the promise of the internet, and the advantages of an electronic mailing system in particular, had become obvious to techies paying attention. Still, internet pioneers of the day came to realize that email, as this electronic mailing system was called, presented its own challenges.
“In particular, the easy and low cost of sending electronic mail, and in particular the simplicity of sending the same message to many parties, all but invite abuse,” IBM researchers Dr. Cynthia Dwork and Dr. Moni Naor explained in their
