Is the 'real barrier' to attack bitcoin's consensus 33.34%, rather than 51%?

Question

Saw a random tweet thread that claimed that the "51" in "51% attack" was misinformation, and that in reality only 33.34% of hash power would be needed for a bad actor to attack the network.

I was skeptical, but one of the posters linked to a talk by Dr. Leeman Baird where, as far as I can interpret, he explains that if you put a firewall around 1/3rd of the hash power and refuse to allow it to talk to the other 2/3rds, then you only need slightly more than half of this remaining 66% (33.34%) to maliciously attack the network. (The relevant part of the video begins at 1:01:08 or so).

I sort of get it as a concept, but as one of the students asks, it seems prohibitively difficult for a bad actor to cordon off 1/3rd of the world's hash power with a firewall. As they ask, is building a firewall around 1/3rd of hash power significantly easier than obtaining the remaining 18% of the hashpower they would've needed (18+33=51%) to conduct a standard 51% attack? This seems like a great question, but Dr. Baird casually responds that China already has a firewall around all of their internet, so doing so is pretty simple since it already exists.

Wouldn't the hash power just move? He explains that recognizing that it has been cordoned off would be difficult and thus makes this solution infeasible.

Is this legit? Would love for someone to give insight.

Answer 1

In this proposed attack, you need more than just hash power. However, if you assume that you can partition the network as this attack imagines, you need no hashing power at all.

If I can split the bitcoin network in half, I can deposit the same bitcoins into two exchanges, one on each half of the split. I can wait for both deposits to accumulate as many confirmations as the exchanges require, trade them for some other crypto, and withdraw the other crypto.

So if you can partition the network, you don't need any hashing power at all to double spend bitcoins. And if you can't partition the network, you still need >50% to double spend.

So I don't think that the existence of these kinds of attacks makes the >50% figure invalid. There exists all kinds of attacks that requires less than 50% of the hashing power (as little as none at all) and something else to launch an attack.

Answer 2

The funny thing about these absurd hypotheses that keep popping up is that if the assumptions involved in executing such a thing were true then they could easily become the richest people in the world just by executing this plan. But they never have the courage to because they all cut corners with the assumptions they make along the way. If you can't tell the main reason they need to attack Bitcoin is because they are trying to grasp the majority share of an unregistered "crypto" security called Hedera Hashgraph which is a completely censorship enforcing permission requiring model of a blockchain.

I can go into the details about why you can't force reorganizations with 30% of the network hashpower if you really don't see how that is impossible, but actually this 50% attack network hashpower thing is really just misbehavior that individual users could opt out of if they were to notice it. Just like in this crazy model of an attack the attacker "firewalls" the rest of the network away. If they do that they consent to having no one actually using bitcoin validate their blocks and they will never be included in the main chain. Seems bat shit crazy to me. Not to mention that there are so many individuals involved in 30% of the network hashpower, good luck getting an army of self serving miners to do an attack just because you asked them to. They would rather earn coins honestly like a sane person.