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Comment by karpierz | Hacker News Reader

> i'm not sure i follow this. what is an entity? how are they disrupting the network?

It's answered in the article:

> They argue this reduces the threshold for a so-called 51 percent attack. "If a node operator's self-interest is to be dishonest, then there is no explicit penalty for doing so. Moreover, the number of entities necessary to execute a 51 percent attack on Bitcoin was reduced from 51 percent of the entire network (which we estimate at approximately 59,000 nodes) to only the four most popular mining pool nodes (less than 0.004 percent of the network)," the study found.

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ahh yes, there's some confusion here. it's not 51 percent of the entire network, it's 51 percent of the hashpower.

it's true that much of the hashpower is concentrated in the hands of a few pool operators, but if i recall, some "getblocktemplate" upgrades that took place around 8 years ago reduced the level of control that the pool operators have. that is, individual participants in the pool aren't mining blindly and would also have to collude. i'd have to look deeper to verify this though.

edit: to follow up, yeah it's true that stratum v1 relies on pool operators, but again it's monitored by gigantic metaphysical libertarian grizzly bears. getblocktemplate delegates transaction picking to participants, but it seems to be in less use and stratum v2 attempts to solve the issues with both.

i don't know what the main pools are using in practice (probably stratum v1 over ssl).

I think they are claiming it's less than 51 percent of hashpower - because they can reduce/disable the 51% by attacking some centralised points, including:

- The c20% of nodes that have outdated software could be eliminated - The c60% of nodes that run on the three ISP's could theoretically be blocked by a nation state if those ISP's could be controlled.

i.e. it might be more like 51% of 30% = 15% of hash power, which are the 4 entities.

right, but those "nodes" are basically proxy nodes which fan out to thousands of individual miners which are actually burning the hashes. since downtime is extremely costly, i expect that those operators to have multiple geographically distributed proxy pool leaders ready to be switched on at a moments notice.

for the purposes of an entity that can be attacked, yes, the pool leaders are such... but since the pools are just proxies and the actual miners have incentives to stay online, i imagine new pools would form pretty quickly.

finally, everyone focuses on the 51% attack as the end-all, be-all. the only net effect of a 51% attack is that someone might be able to double spend. the cost of running the attack would require that the double spend be pretty massive to make it worth it, and for any massive transaction anyone prudent would wait until said transaction was quite deep in the chain before considering it done (thus requiring even more hashpower to undo it).

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