I'm not totally sure, and would be interested to hear other views. Here's what I was told before: https://news.ycombinator.com/item?id=5548219

Mining verifies all transactions in the network. That's the whole point of the system, making sure that transactions can't be faked. In order to fake a transaction, you would need to control 51% of the total hash rate of the Bitcoin network, which is impossible.

"In order to fake a transaction, you would need to control 51% of the total hash rate of the Bitcoin network, which is impossible."

Impossible?! The claims about why this polynomial-time attack on Bitcoin is not really a problem seem to get more outrageous with each passing day.

I find it interesting that you simply assume that there is no other attack on Bitcoin. There is no proof of this. There is not even a good enough definition of the security goal of Bitcoin to allow for such a proof.

Call it economically improbable. Right now you could maybe get 51% with a 10-20 million dollar investement in ASICs. If you took control of the network and started forging transactions, bitcoin would no longer be useful and all those coins you stole wouldn't be worth very much.

EDIT: I vaguely remember the Linode hacker mention that a more reasonable attack possibility would be if you slipped an backdoor into the popular bitcoin client libraries, and then it could be used to steal.

edit2: spelling.

Maybe you only want to deny confirmations to your enemies. I can imagine that the US government might want to prevent people from making donations to Wikileaks. Maybe someone just wants to destroy Bitcoin, for reasons that are beyond your imagination.

Really though, trying to figure out your attacker's intentions or goals, or their willingness to commit resources to an attack, is a fool's errand. This is even more so when your system has known and exploitable weaknesses. The Germans learned this lesson the hard way with Enigma:

https://en.wikipedia.org/wiki/TICOM

I guess that by "Godwin's Law of Nazi Analogies" this discussion has officially run its course :P.

I think I agree with the major implications of what you are saying: bitcoin hasn't demonstrably withstood nation-state levels of attack effort, so calling anything impossible is premature.

If the bitcoin network survives for long enough [which can't be taken for granted] this will eventually happen, but it hasn't demonstrably happened yet.

> In order to fake a transaction, you would need to control 51% of the total hash rate of the Bitcoin network, which is impossible.

Relevant to the article that this thread is linked to, it wouldn't be at all impossible if you are the single high-rate producer of by far the most efficient mechanism for mining bitcoins, and you really wanted to disrupt bitcoin.

(It might be economically irrational for anything that seems to a sane person to be a plausible assignment of utilities, but then, lots of socially destructive acts that actually occur in the real world meet that description.)

Sure, but I'm pretty sure that the only reason you need to keep adding and adding ever more capacity is to prevent someone else coming along and doing the 51% attack, right?

Other than that, adding capability doesn't benefit the network, it burns a lot of power as people effectively just burn electricity to try to increase their share of a fixed payout.

> I'm pretty sure that the only reason you need to keep adding and adding ever more capacity is to prevent someone else coming along and doing the 51% attack, right?Other than that, adding capability doesn't benefit the network, it burns a lot of power as people effectively just burn electricity to try to increase their share of a fixed payout.

Sure, if you want to efficiently allocate resources, all bitcoin miners could get together as a cartel and limit the overall hash rate to 1Mhash/hr, and collectively the bitcoin transactions network would consume a lot less power.

However, the temptation would always be there to add a little extra hash power to the network and network to claim more of the mined blocks and transaction fees. And pretty soon you'll be back where we are today, with each person acting in their own selfish interest, addiing as much hashing power as they can afford to run to get as big a share of a fixed pie as they possibly can.