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Comment by judk | Hacker News Reader

Not gonna happen, the depth isn't there.

Even today's $1k BTC is speculation at the edge of the market, 1million BTC as a batch only fetch about $50m worth of interested buyers.

Here is one ting I don't understand, though: suppose I am a billionaire black hat VC, and I wanted to steal Satoshi's coins. Could I invest a half billion dollars and brute force a majority-coup attack on the blockchain? Of not now what about when those $ figures are 10x? Even if bitcoin gets 100x more popular, it won't be 100x more network miners, it will be people buying BTC and trusting the block chain published by coinbase and whoever.

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The computational power to attack the network grows significantly faster than the price of Bitcoin (and this is pretty much guaranteed to continue, by design). Attacking Satoshi's coins would be among the hardest, because you would have to attack the very earliest parts of the Blockchain which have tens of thousands of blocks protecting them. Half a billion dollars wouldn't come close at the current difficulty level.

Further, performing this attack would invalidate all Bitcoins created after that point (which is the vast majority of them), so the Bitcoins you stole would be worthless.

To add to this: The "official blockchain" is the one with the most computational work expended to create it.

A 50+% attack operates by rewriting history back to a certain depth in the blockchain by providing a new chain of blocks with more computational work, back to a certain point.

I think the bitcoin devs also put in certain "checkpoints" just to be even more certain... i.e. blocks that are "officially permanent" (which also makes all prior blocks in that chain "offiically permanent").

Maybe someone could tell us about that.

Ah yes, I forgot about checkpointing. The reference client has certain blocks hardcoded in it to signal the official chain. Only transactions in blocks made after the latest checkpoint can be overridden in a way that the reference client would accept. So to steal Satoshi's coins, you would also have to get people to switch to your own client with different checkpoints. At this point, it really wouldn't even be Bitcoin anymore.

> I wanted to steal Satoshi's coins. Could I invest a half billion dollars and brute force a majority-coup attack on the blockchain?

No - controlling a majority of the compute doesn't allow you to steal some unrelated users bitcoins.

You'd have to brute force their private key to do that, which is an infeasible computational challenge.

Controlling a majority of the compute would allow you to 'double spend' coins you have, but that's a different problem.

Wouldn't BTC lose all value if there was a majority attack? Because surely such an attack would be quickly detected.

You can't "steal" anyone's coins, you may "take back" the coins you have sent someone with enough power, though.

If you had half a billion dollars, it would be much more profitable for you to mine bitcoins.

Or invest it in something with tangible value...

This of course assumes that you'd use an exchange to sell the coins.

There are other methods of selling coins. Larger transactions tend to happen off-exchange.

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