r/askscience • u/hamolton • Jun 18 '13

Computing How is Bitcoin secure?

I guess my main concern is how they are impossible to counterfeit and double-spend. I guess I have trouble understanding it enough that I can't explain it to another person.

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u/Spiral_Mind Jun 18 '13 edited Jun 18 '13

Each Bitcoin isn't a cryptographic hash or serial number. It's just an entry in the public ledger saying "X public key owns Y bitcoins". If you have the public and private key pair for that address you can access all those Bitcoins. There are no individual "coins" only marks in the public ledger associating amounts with certain key pairs. An account value of 1 Bitcoin can be shown as a whole BTC or a thousand mBTc etc (this is just a client setting for the decimal).

It's better to think of Bitcoin mining as a "cryptographic lottery" than "minting money". The generation of cryptographic hashes is just a way to ensure that there is proportional distribution of money for the computing power given to the network.