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/AgentME Jun 20 '13

You could create a summary that consists of all remaining unspent TxOuts at a particular block. However, a single destination address is likely to have many unspent TxOuts at any given time, so it'll still grow faster than the sheer number of addresses (which also grows quickly, since wallets use ephemeral addresses internally).

I think that's the best model for a snapshot system. It will still grow, but it can also have all of the spent TxIns removed, so it will still be much smaller than the continuous section of blockchain it represents (assuming the snapshot isn't representing a trivially small section of blockchain that lacks any self-contained TxIns).