It was always more of a theoretical concern.

At least since 2014 onward.

Best thing is, even if somebody did it it wouldn't affect the coins in your wallet.

Worst case: a transaction is first confirmed, and then not there anymore in the new chain.

People used to wait 6 blocks before considering a transaction final to guard against that. (And the possibility of accidental non-attack chain splits)

- The attacker would have to keep up the hash rate indefinitely to maintain its grip

that's the situation

bitcoin is far beyond government intervention, and inter-governmental cooperation is basically a matter of military theory, so, yeah, miltary theory says a single currency is great and you can't do that with fiat, you can't do that with fiat

did i mention you can't make an international currency without coercion? and that leads to rebellion. so, yeah

nostr:nprofile1qqs8fl79rnpsz5x00xmvkvtd8g2u7ve2k2dr3lkfadyy4v24r4k3s4sppemhxue69uhkummn9ekx7mp0qy2hwumn8ghj7un9d3shjtnyv9kh2uewd9hj7qg4waehxw309aex2mrp0yhxummnw3ezucn89ur9eu8h would say that it is quite feasible when the block template is owned by one large entity, while everyone sells their hashes to them via fpps.

The threat lies in the centralization of the hashrate not in an external force joining the network.

We will have to trust them not to double spend or hold transaction from the mempool (we dont want to trust anyone).

mempool screenshot from now :

You got most of it nailed.

Let's say that we're dealing with an irrational actor that cares not for profit or anything else but sheer incentive disruption.

If 51% attacks then they really only at most can control the chain tip at best , if they even try a 1 block reorg they have to re do the work of 10 blocks to even outpace the network working honestly. It's only a 1% advantage.

Check out this episode for more.

https://open.spotify.com/episode/79d1usUx9IYTO5zlCqMvQY

It will just happen from centralized pool miners.

My impression is that even if it worked it would effectively be a hard fork, and the existing nodes would refuse to recognize transactions as long as they have the existing software.

But I could very well be wrong, because I'm still pretty fuzzy on how all of this works, but it has stuck with me that nostr:nprofile1qyv8wumn8ghj7urjv4kkjatd9ec8y6tdv9kzumn9wsq3vamnwvaz7tmjv4kxz7fwwpexjmtpdshxuet5qyvhwumn8ghj7um9dejxjapwdehhxenvv9ex2tnrdaksqgqyey2a4mlw8qchlfe5g39vacus4qnflevppv3yre0xm56rm7lveyr9lldz recommends not upgrading nodes with new software immediately.

Not your rack, not your hash.

If you dont control the hardware you dont control where it mines and all hosted mining is white market.

The adversary is the threats from the state.

white market is anyone who abides by government regulations

black market are those who ignore or subvert it

White market mining is and always will be a security risk.

lets says 51% of hash is institutional mining in the US. A law is passed that any miner in the US must enforce OFAC censorship.

That 51% is now doing the opposite of securing the network.

https://github.com/libbitcoin/libbitcoin-system/wiki/Jurisdictional-Arbitrage-Fallacy

And it doesnt matter where you take your hashrate if 51% is enforcing censorship.

If you are in the US do you think giant mining farms are going to relocate or even be allowed to take their equipment out of the US to subvert US sanctions? Pools dont matter they are all centralized and trusted.

Much better to educate people about the actual security model and risks of white market mining.

Building out substantial hash defense beforehand makes things a lot easier instead of waiting to respond to an active 51% attack

#bitcoin cannot be both permissioned and permissionless at the same time

https://github.com/libbitcoin/libbitcoin-system/wiki/Permissionless-Principle

You missed the role of the pools. He who controls template construction controls the hash.

Even if someone acquired 51% actually executing the attack *profitably* is not easy. They'd have to exchange their own properly acquired bitcoins with a huge value for something in real world of that value (a huge mansion or a company maybe?) but irreversible in nature even if people figured it out and attempted to use legal means to restore it. I don't think there's any such thing. Maybe a huge amount of physical gold if one can find how to hide it securely but even that is super hard.

bitcoin is a game in which participating is winning. not playing the game is losing.

It's mainly prevented by incentives.

A 51% attack is very expensive & has a very low return unless your aim is to discredit Bitcoin.

Miners are generally very bullish on Bitcoin. They're financially incentivised to support Bitcoin since that's what they're paid in & use as a treasury reserve.

A 51% attack isn't a death sentence for Bitcoin. It will take a 51% attack to occur for most people to actually realise this though.

The bigger risk is the censoring of certain transactions which is why there's such a drive to decentralize block template creation & mining pools. It only takes 1 block to add prohibited (& financially lucrative) transactions to the timechain. Someone will always take the prohibited sats.

And another possible deterrent is that even if they did it - the rest of the community (basically the nodes) could unite and change the codebase of Bitcoin to use a different hashing algorithm and that would make all those ASICs obsolete.

Decentralized systems are very robust!

Doing such an attack isn't a one of attack. They need to keep doing this every ~10 min. when a new block is mined, to stay in control of 51%.