The zeroth innovation is a Proof of Work implementation: HashCash [1], invented 1997. After all we stand on shoulders of giants. [1]: http://www.hashcash.org/

The zeroth innovation is a Proof of Work implementation: HashCash [1], invented 1997. After all we stand on shoulders of giants. [1]: http://www.hashcash.org/ http://www.hashcash.org/ Edit: Added an explanation. HashCash was an idea to thwart spam by forcing spammers to do work. It works similar to Bitcoin's Proof of Work: Use a nonce and hash the text together with a nonce. Does the hash start with some zeroes like this: 0000bbab945399d0f80395c65e2ba4c93c89ada8? You are done. Else retry with a different nonce. So if the spammer's computer has to calculate HashCash for about one or two seconds for each e-mail, he won't be able to send millions of them. That was the idea.