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When Satoshi Nakamoto published the original white paper describing the Bitcoin protocol, they referenced Hashcash and B-money. B-money is a proposal for an electronic cash protocol, similar to Bitcoin. Hashcash is the proof-of-work algorithm used in Bitcoin.
P2P, digital signatures, proof-of-work and electronic cash protocols existed before Bitcoin. What exactly were the novel contributions of the Bitcoin protocol?
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b-money proposes to pay for money minting by means of proof-of-work. The minted money then has the value of the expended computational power.
For value transfers it either relied on a synchronous unjammable channel and arbitration, or on a set of trusted servers that had to be regularly audited by the other network participants.
In other words, b-money used POW to create monetary scarcity with manual supervision.
Bitcoin instead introduced the use of proof-of-work to create scarcity in the truth source: By electing only one network participant to extend the blockchain through the mining lottery, Bitcoin manages to forgo arbitration or trusted servers, yet manages to create convergent synchronization of the network's state in an asynchronous manner.
It's late and I'm tired. Please don't hesitate to point out the mistake I've surely made in the above. ;) Good night. – Murch – 2016-09-06T23:37:29.503
1B-Money didn't use PoW for consensus. It suggested either a syncronous unjammable channel, or a set of trusted servers that would put up a deposit to allow them to be fined (presumably by a vote of the other, honest, servers.) – Nick ODell – 2016-09-06T22:49:56.137