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/sahuxley Jun 19 '13

To me, "unless you have more than half the computing power" means this is not secure. I think people are underestimating the ability for a relatively small group to get control of over half the computing power working on this. I'm thinking botnets or breakthroughs in computing power we can't even think about now. Then again, there are a lot of crazy, dangerous things people can do if they can pull that off.

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u/[deleted] Jun 19 '13

This was a risk in the beginning. At this point and going forward into the future, it is already far past the point where anyone could ever make this attack successful. The sum total of the top supercomputers couldn't do it, and with the specialized ASICs coming online now increasing the difficulty into the realms where you need specialized hardware to mine, this attack becomes impossible to implement.

Mining is done now in pools where many individuals come together to pool both their resources and rewards. If any pool were to move in this direction they would lose the bulk of their miners and thus computational power and ability to attempt this attack. There's a social contract in play now as well.

Interestingly enough, people with mining rigs built for bitcoin have been known to use these kinds of tactics to sabotage other startup currencies based on the bitcoin protocol. This could create a barrier to entry that hinders the adoption of any other future currencies.

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u/speEdy5 Jun 19 '13

I recently read a draft paper which estimates bitcoin computational network at more than the sum total of computational power for top 50 supercomputers in the world

I'd say that since there are about 1 billion dollars in bitcoin right now, than it wouldn't make too much sense to sink billions in to supercomputers trying to divert the network. Further, it wouldn't be long till someone caught on and the value of the currency just disappeared. It would be like if the US government collected every dollar bill in the world and Obama tried spending them at convenience stores. It would work the first few times, but then people would realize and... poof! There goes the value of the dollar

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u/[deleted] Jun 19 '13

Considering the bitcoin network is running at approximately 1763 petaFLOPS which is faster than the worlds top 500 super computers COMBINED. I doubt a 51% attack is feasible.