On 31 October 2008, a message arrived on a cryptography mailing list with a link to a short paper: Bitcoin: A Peer-to-Peer Electronic Cash System. It was nine pages long, signed Satoshi Nakamoto, and it opened with one sentence that still sums up the whole project.
The problem with trusted third parties
Online, every payment passed through a bank or a payment company. The introduction explains the cost of that: the middleman must settle disputes, so payments can be reversed, so merchants must ask for more information about their customers, and a certain share of fraud is accepted as unavoidable. Small, casual payments become too expensive to be worth it.
Cash in your hand has none of these problems: you give it, it is gone, nobody can cancel it. What was missing was a way to do that over a network, between strangers, with nobody in the middle.
The one hard problem
Digital things can be copied. A file you send is still on your disk. Earlier digital cash systems solved this with a central server that kept the list of who had spent what. The paper's goal is to remove that server and still stop anyone from spending the same coin twice.
▶ SEE IT IN THE MACHINEThe first page of the paper stands, in gold, at the back of the hall. Its title, author and opening lines are the real document.