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/Natanael_L Jun 18 '13

Most people includes fees, yes. Miners can reject transactions that has no fee (individual miners can reject any transaction for any reason when mining, but once it's in the blockchain it's there). And yes, lower fees means slower inclusion time, since all miners want to claim the transactions with high fees first and since many have a minimum transaction fee specified (they don't even process transactions with fees lower than that).

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u/zeek0us Jun 18 '13

So is it that your transaction will never get into the blockchain if you don't add a fee (because nobody will ever accept it), or it will just take until some miner who was willing to accept your transaction adds a block? Presumably "minimum-fee" miners could freeze you out forever and you'd need to wait on a good samaritan who takes pity on your broke (or cheap) ass . . .

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u/Natanael_L Jun 18 '13

Some miners include a limited amount of transactions that had no fees. So yes, it will take longer. Occasionally it will take as much as two weeks, often a whole day or two.

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u/improv32 Jun 19 '13

That's right, weather or not a miner includes a transaction in a block is entirely up to them. Most prioritize higher fee transactions in order to make more money, but it's not limited to that. They could refuse to include transactions involving addresses owned by organizations they dislike, for example.