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Comment by Devilboy | Hacker News Reader

Would it be possible to hire a large number of servers just for a short time and take control of the whole chain? Is it just a matter of time before this happens? You could combine various cloud providers' servers and black market zombie machines.

If Bitcoin continues to grow in popularity at a sufficient pace it should be safe, but the minute it becomes cost-effective to attack it, it will fall.

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So, the network has generally become much more expensive to fail. It currently employs something like 10x the K computer (Top 1 in the Top 500) worth of compute. There are probably a few organizations that could get that compute power together for a while, but you'd have to ask 'why?' and 'for what reason?'

If you want to send a lot of money through Bitcoin transactions, I suggest you estimate expected compute cost of subverting the number of validating transactions you are going to wait to secure it, and using that as a baseline.

E.g. subverting 10 transactions in a row with > 50% likelihood (but doing so without anyone noticing, that is, timed appropriately) would take something like 10x the current compute power for about an hour, = close to a million dollars? hundreds of thousands certainly.

Ergo, wait a day for a $1mm bitcoin transaction to clear, and similarly, don't worry about a $500 transaction at all.

Only a million dollars? That means the government can shut down Bitcoin any time it wants.

Except that forensics will allow us to identify the fraudulent block chain, and ban all the relate computers. "Shut it down" really just means "force the Bitcoin community to step it up".

How do you ban all the related computers?

You can't easily "ban" these things, since it's a decentralised P2P system. The whole point is to prevent anyone (original creators, banks, a government, etc.) from being able to interfer with it. It does mean the system fails like that.

Everyone is free to ignore whatever block chains they want to. I can refuse to honor blocks built off what I consider fraudulent block chains.

Would you able to trade with people who hadn't ignored those bloc chains?

The government can already shut it down. They can make laws. There are lots of laws about money laundering and record keeping, and paying taxes that can be used against BitCoin.

You'd have to rent servers with ATI GPUs in them, but nobody rents those.

Is it something special about the ATI GPU, a particular instruction perhaps? If a NVidia GPU would work you can rent an EC2 instance with them from AWS.

http://aws.amazon.com/hpc-applications/

AMD/ATI GPUs happen to be a lot faster for hashing than NVIDIA's. Partly because of a key design difference, and partly because they happen to have a fast 32-bit right rotate instruction.

Details here: https://en.bitcoin.it/wiki/Why_a_GPU_mines_faster_than_a_CPU...

In theory yes, but it gets more comutationally hard (and hence expensive) as time goes on (this is to account for moore's law). Also, there has been no reason to do it, since it's not worth the money.

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