Hacker News Reader

Comment by heliumcraft | Hacker News Reader

good luck getting the computer power to do a 51% on Bitcoin or Ethereum. The hashpower used in Bitcoin is mind-boggling.

View on HN

You only need to spend as much as the miners already are doing. With proof of work, if it is feasible to run, it is feasible to attack. And vice versa, if it is not feasible to attack, it is probably not cost effective to run.

Bitcoin may be wasting enough electricity to put it out of reach of small-time attackers, but a nation adversary could outspend it for as long as necessary.

But what does the attack get you? Sure you could mine empty blocks and double spend, but that would hardly be worth the investment. Besides, if payment processors detect the hashing rate doubling overnight they can simply require more confirmations.

If a nation state invested in permanently disabling bitcoin that would require a big investment in ASIC's, at which point I imagine a bitcoin fork would be introduced with a slightly different PoW, but that's just speculation.

> a bitcoin fork would be introduced with a slightly different PoW

And then what? Either you're falling back to mining on CPUs or GPUs, which the attacker would presumably have a large amount of, or you're manufacturing a new batch of ASICs, which is just as expensive for you as for an attacker. The point remains that an attacker can win by spending only slightly more money than the defender.

Whether that's "worth the investment" is up to each individual actor, apparently it hasn't been yet.

"The point remains that an attacker can win by spending only slightly more money than the defender."

It's actually only slightly more than the sum of the defenders (assuming as we are for the sake of argument that everyone is buying efficiently). If what you said was true BitCoin wouldn't even have gotten to where it is now.

This has happened in the past, see http://arstechnica.com/security/2014/06/after-reaching-51-ne... .

I agree the required power must have grown since 2014. But not knowing by which factor, one can only assume it's still feasible.

I can't find any source for it, but I remember reading not so long ago that 2 or 3 mining pools were responsible for 2/3 of the total bitcoin mining power. That's not something in favor of trusting the blockain as infallible.

it has increased by a factor of ~153x

https://blockchain.info/charts/hash-rate?timespan=all

2014 -> 10,436 TH/s 2016 -> 1,536,337 TH/s

The attack was in june, when it was ~ 100K TH/s rather than 10K. The factor becomes ~15x instead of 150x. But I must admit I don't know if that makes such an attack still feasible.

This is why Bitcoin is going to win - it is good enough for a lot of use cases and getting better. At the same time, it's the most widely accepted and the most secure. The network effect is too strong to overcome unless you offer something Bitcoin cannot.

Reply on news.ycombinator.com