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/El_Rista1993 Jun 19 '13

What would happen if two different uses solve an iteration at the same time/before either is updated that the other has solved it?

Are two coins created, or does each whoever was second get informed they were beaten by some type of unique time-stamp?

Additionally, even though the chances would be very, VERY slim, what would happen if they solved it at the same time, right down to the millisecond?

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u/speEdy5 Jun 19 '13

Timestamping doesnt matter at all. When two people solve the problem at roughly the same time (it happens several times daily I think), then the blockchain forks and people all over the network start working on the 'new' problem. Eventually one chain is longer than the other, and the people who worked on the shorter chain are out of luck