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Comment by atgm | Hacker News Reader

> But if it would restore public confidence in the protocol and economy

It actually scares me. If any private body or group could somehow amass 51% of the miners in some way, they would then control the currency.

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No, you basically only control the order of transactions: https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_...

Thank you for the clarification!

You can also rollback history and block transactions which you disapprove of from happening with 100% probability. Other than that, no major problems.

You are correct, but I feel like it must be physically impossible for you to comment on Bitcoin without being snarky.

Technically, you need 100% hashing power in order to block a valid transaction forever.

Oh, you can certainly use your 49% to publish a block or two, or even twelve in a row -- good for you, probability sometimes works like that -- but eventually I will have more blocks mined privately than the rest of the network does publicly, at which point I publish them (with my choice of confirmed transactions) and all your work, the transactions which you chose to confirm, and your mined coins just go down the memory hole.

The mined coins, sure, but you can include the transactions that were omitted in the revealed fork in the blocks after that. That's why the document states An attacker that controls more than 50% of the network's computing power can, _for the time that he is in control_

I'm not saying that when this would happen it would be a good day for Bitcoin by the way.

I don't understand. I think "for the time that he is in control" means "as long as he has > 50% hashing power". No need for 100%. As long as he has > 50% he can eventually overtake any fork that includes a new transaction.

In theory, given enough time (a very long time), someone able to maintain 50.0000001% of hashing power could eventually rewrite the entire blockchain after the genesis block.

If you have a 51% forever you can refuse to chain the blocks that contain the unwanted transaction. Every time it's added to a block you just fork the chain, and as you have the 51% hashing power your fork will eventually win.

The time to crush the other fork depends on how much hashing power you have. With 60% you will generate 60 more blocks in a day that the other fork, in average. With a 51% you will generate 6 more blocks per day. With a 50.1% you will generate only 1/2 extra block per day, so you need a few days to win.

Well, that always has been and always will be true.

I think there's a difference between something being factually true (you will die) and something being imminently factual (you have cancer).

Those are really negatively-biased examples, sorry.

It's not one private body. I think in this case one might say all MtGox customers would be asking miners to do that.

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