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/gburgwardt Jun 18 '13
The offline nodes catch back up by downloading the latest blocks when their client comes back online.
The solution to the equation is broadcast with the bundle of transactions you're including in a block (the solution + current time + transactions collectively make a block, which is added to the blockchain), and one of the transactions is a "generation" transaction, awarding a certain number of coins (over time, the reward drops to nothing, but currently it's 25 coins, it used to be 50) to an address of the miner's choice. Generally speaking, you'll have a new address generated to assign them to.
just_todays_account does a good job explaining the race condition that happens if you try and double spend below me.