Bitcoin
A purely peer-to-peer version of electronic cash would allow online payments to be sent directly from one party to another without going through a financial institution.
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Trust replaced by work
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Nakamoto's design chains transaction blocks with SHA-256 proof-of-work. Honest majority hash power makes rewriting history exponentially costly. The ledger is public; identities are pseudonymous.
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The double-spending fix
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Digital files copy for free. Bitcoin solves double-spending not with a bank but with a timestamp server and longest-chain rule. The network is the mint.
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Beyond the asset
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Whether or not you care about the price, the paper is a landmark in distributed consensus thinking. It launched a decade of debate about energy, governance, and what "decentralized" actually means in production.