On 5 April 2013 11:48, Mike Hearn <mike@plan99.net> wrote:

51% isn't a magic number - it's possible to do double spends against confirmed transactions before that. If Michael wanted to do so, with the current setup he could, and that's obviously rather different to how Satoshi envisioned mining working.

Thanks for pointing this out. I guess 51% is mainly of psychological significance.

However, you're somewhat right in the sense that it's a self-defeating attack. If the pool owner went bad, he could pull it off once, but the act of doing so would leave a permanent record and many of the people mining on his pool would leave. As he doesn't own the actual mining hardware, he then wouldn't be able to do it again.

Totally see the logic of this, and it makes sense. But I dont think the only risk is in terms of double spend, but rather

1) vandalize the block chain which may be difficult to unwind?

2) use an attack to manipulate the price downwards, then rebuy lower

As bitcoin's market cap grows, incentives to move the market will grow

There are also other mining protocols that allow people to pool together, without p2pool and without the pool operator being able to centrally pick which transactions go into the block. However I'm not sure they're widely deployed at the moment. It'd be better if people didn't cluster around big mining pools, but I think p2pool still has a lot of problems dealing with FPGA/ASIC hardware and it hasn't been growing for a long time.

I guess the market will decide which algorithm is used, but as a community we can perhaps review the different mining protocols and order them in terms of risk ...

On Fri, Apr 5, 2013 at 11:30 AM, Melvin Carvalho <melvincarvalho@gmail.com> wrote:

There was some chat on IRC about a mining pool reaching 46%

http://blockchain.info/pools

What's the risk of a 51% attack.

I suggested that the pool itself is decentralized so you could not launch one

On IRC people were saying that the pool owner gets to choose what goes in the block

Surely with random non colliding nonces, it would be almost impossible to coordinate a 51% even by the owner

Someone came back and said that creating random numbers on a GPU is hard. But what about just creating ONE random number and incrementing from there ...

It would be great to know if this is a threat or a non issue

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