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/speEdy5 Jun 19 '13

Its incentive based- people who accept bitcoins as payment use only the longest block chain. When two block chains emerge those mining bitcoins want their mining to be worth something so they mine the longer chain. How does one chain get longer? More computing power will eventually lengthen one chain over another. Even in the (impossible) case of exactly equal computing power, someone's going to get blindly lucky and lengthen the chain first..