[olalonde]

First, that figure is way off. Marathon alone has a market cap over $4B and controls less than 5% of the total hash rate.

Second, the system only seems vulnerable if you ignore economic incentives. A 51% attack isn't just technically difficult - it's economically irrational. Pulling it off would cost billions, and even then, there's no clear way to profit from it. The only scenario where it makes sense is a non-economic actor (e.g. a hostile government) aiming to disrupt Bitcoin. But even then, that investment could be neutralized by a fork that tweaks the mining algorithm, instantly rendering the attacker's hardware obsolete.

[wmf]

It's true that buying 51% hash power would cost far more than $4B. Some people assume that you could rent 51% hash power for a short time (like a day) to do the attack.

[osigurdson]

According to ChatGPT (bad source I know but can't find it anywhere else), the entire value of the entire mining network is about $6B. What do you think it is?

[wmf]

Closer to $20B. MARA owns $1B in equipment for example.

[jowea]

If we're talking about a fork, couldn't a fork just ignore the attack? The normal miners aren't forced to use the attacker's blocks after all.

[olalonde]

The problem is that there's no reliable way to identify who mined a given block, so you can't simply have the network "ignore blocks from the attacker." The coinbase transaction may contain identifying info (e.g., pool name) but it's not mandatory nor authenticated.

[daveguy]

Why would someone want a random block chain company to own 5% of the possibility of destroying their holdings? What if the company gets co-opted by some nation state actor? Bitcoin really seems like a terrible place to keep wealth.

[olalonde]

I'm not sure I follow your question. Who is the "someone" you're referring to? And what do you mean by "destroying their holdings"? Even in a 51% attack, an attacker can't alter wallet balances or arbitrarily erase funds.

Also, what alternative "place to keep wealth" is truly immune to a nation-state actor? Cryptocurrency is actually unique in that, with something like a brainwallet, seizure can be made practically impossible.

[wmf]

If you own 5% of the hash rate you have ~0% ability to attack the network.

[daveguy]

Yes, but if you're a nation state with dictatorial control over a nation's resources, +5% might be all you need.

[osigurdson]

I guess all of these arguments have existed since the beginning of Bitcoin (51% attack, miner centralization, supply chain centralization, etc). What we do know is while it theoretically could happen it hasn't happened yet.