Too late for 51% attack

[bitbollo]

There are more risks for the miner and probably this cannot be a real threat.
Not only because the network has become bigger and most of bitcoin has been mined...
Even if nowadays all biggest miners would collide to make their syndicate, they would never be able to collect all blocks.
Once they would collect it they could just split the effort, just create another pool.
In the meanwhile they have to compete with all others miners and placing the whole network at risk. Just to mention.. once cex.io has reached this critical level they have decided to limit the size of their pool...

[CryptoYar]

Your instinct is correct. Mining pools are not owners, but rather managers. Hashrate of a pool to which is pointing thousands of miners worldwide, every one of which being able to change target pool whenever they want. Otherwise, miners would simply walk away and attack would be canceled if pool tried any shady business.

There is also economic reward reason. Successful 51% attack would have big impact on Bitcoin price and people would lose faith in it. Those with hashrate to be able to do so are the ones most likely to lose money if BTC goes down in value. For those who own Bitcoin and mining gear, attack is self-ruining. This is because people are confusing pool hashrate with pool ownership. They are two entirely different ideas and understanding that difference makes the 51% threat from big pools imaginary, not real.

[treesintheforestooh]

Not sure I can add any more value to an old horse that died so long ago no one remembers where it's buried... but, to all who bring this up, don't think about the possiblity (everything is possible) and don't think about the likelihood (never a zero chance of anything happening) but think about "to what end?".

What could a 51% attack possibly gain for its instigators? What could be enough to cover the financial cost of that?

Then you realise a few things and understand this isn't happening, and if it does, it won't have lasting repercussions on the good actors.

A 51% attack doesn't have to come from someone/an organization/a "network state" type actor looking to make money.

Indeed, when/if the next attack comes it will very likely be political and ideological.

[legiteum]

A 51% attack would most likely come from a clandestine takeover of the systems of a few of the mining companies. This could be done by a hacker group, but more likely a major state actor like Iran, Russia or North Korea.

As for the motive, there might be some scenario where the Bitcoin network getting fouled up could make somebody a lot of money in some complicated scheme (viz. with perps selling BTC short or something), but as the poster above said, it could be just an act of terrorism or war that was the motive.

It's worth noting at this moment a fact that Bitcoiners don't like to talk about:

Bitcoin's most important defender is the US government.

In other words, the entity that has the biggest job of tracking worldwide terrorists and malign states is the US government, and the US companies that could represent >51% of the hash rate are US companies who would be under their protection.

And then there are the US billionaires who have given the US president a lot of money, many of whom are large BTC holders and would want to make sure the Bitcoin network is protected.

Then there's the US government itself, who is known to own a lot of BTC, and could very well be the owner of the Satoshi coins as well, which would give the US government a reason to help protect the Bitcoin network for pure monetary reasons.

Finally, although he's been selling off his Bitcoin, the US president, Trump, still owns almost a half of a $billion in BTC, so that highly motivating as well.

Fortunately, the US has a very good capacity here, and has enormous capacity to strike back, but one could argue that Bitcoin would be very vulnerable to attack without the USA.

[X-ray]

That is exactly what some people don't understand, those mining pools aren't owner of hashrate, it's just a pool and whoever the hashrate belong to can get out of the pool if they disagree.

I think we've had similar thing where a pool grow beyond 51% of total hashrate and a lot of people pulled out their hashrate to decentralize decade ago.

[stompix]

I don't think the three biggest mining pools hold up to 50% of the network's hash rate, so it won't be possible even if they come together for that mission.

They do and it's even worse , not only do 3 of them have over 51% but the top 5 have over 75%.



But again, it doesn't matter; this one is more concerning if it goes on like this:

51% is getting expensive, the hash rate increased even if the prices are falling, which makes the 51% is even more expensive, but there is always a possibility for that to happen and one with an unlimited amount of money and strong hate towards bitcoin can do that?

Hash rate as sole indicator of security is useless!
What is more secure :
a 500 petahash network when the gear is traded at $10 per gh/s
a 900 exahash network when gear is $4 per th/s ?

What is more secure?
- a trillion network protected by a reward of 50 million a day
- a billion network protected by a reward of 5 million a day?

What could a 51% attack possibly gain for its instigators? What could be enough to cover the financial cost of that?
Then you realise a few things and understand this isn't happening, and if it does, it won't have lasting repercussions on the good actors.

No attacker on Bitcoin with this method will "gain" anythign of it; the costs are just prohibitive for any possible return, if there would be any as we would probably have a roll-back anyhow.
A 51% attack if ever carried out, would have only one purpose: destruction!
But again, this is not a problem for now, in a decade...things might be dicey, and adjustments would have to be made!

 

[buwaytress]

What could a 51% attack possibly gain for its instigators? What could be enough to cover the financial cost of that?

Then you realise a few things and understand this isn't happening, and if it does, it won't have lasting repercussions on the good actors.

A 51% attack doesn't have to come from someone/an organization/a "network state" type actor looking to make money.

Indeed, when/if the next attack comes it will very likely be political and ideological.

I didn't say that it would be about making money, the gain (yes, political or ideological) would still need to be enough to make the cost worthwhile -- politics and ideology in the end has a financial cost or demand. And there is no plausible permanent gain... it would just be burning money and reputation for... ignominy.

No attacker on Bitcoin with this method will "gain" anythign of it; the costs are just prohibitive for any possible return, if there would be any as we would probably have a roll-back anyhow.
A 51% attack if ever carried out, would have only one purpose: destruction!
But again, this is not a problem for now, in a decade...things might be dicey, and adjustments would have to be made!

That was my point. Whatever gain they could think of, would not be enough to justify the cost -- and the roll-back is where I was saying that any potential gain would only be temporary. Good actors will reorg. Faster than the attackers think.

[Aanuoluwatofunmi]

51% attack is one of the reason many thoughts bitcoin could not be secured, but when you look into it critically you will discover that the possibility of this happening is very low because of the hash rate distribution that is not concentrated on a particular country or entities that are mining pools, bitcoin network has been held in a more secured blockchain technology that does not permit for any centralized censorship, this is why it is also impossible to have them manipulate anything about the price or the Bitcoin network.

[legiteum]

No attacker on Bitcoin with this method will "gain" anythign of it; the costs are just prohibitive for any possible return, if there would be any as we would probably have a roll-back anyhow.

Using this method (i.e. simply buying yourself a ton of servers and adding them to the pool), I agree.

But an attacker would most likely just infiltrate some of those companies and infect their code.

A 51% attack if ever carried out, would have only one purpose: destruction!

Destruction would be the initial purpose, I suspect there are schemes one could devise to make money on an attack on Bitcoin, perhaps even a lot of money.

But again, this is not a problem for now, in a decade...things might be dicey, and adjustments would have to be made!

I agree if you are talking about quantum, but Bitcoin's general security threat is ongoing and is monitored every single day by (mostly US, I suspect) authorities. For many security workers working in governments and large private companies, this is a "now" problem and they work on it every day.

[MarryWithBTC]

51% attack is one of the reason many thoughts bitcoin could not be secured, but when you look into it critically you will discover that the possibility of this happening is very low because of the hash rate distribution that is not concentrated on a particular country or entities that are mining pools, bitcoin network has been held in a more secured blockchain technology that does not permit for any centralized censorship, this is why it is also impossible to have them manipulate anything about the price or the Bitcoin network.

I remember some years back that we were so concerned and scared of the 51% attack. There was fud about this attack, even when it was hypothetically impossible to happen, fud makers still found their ways to manipulate the market with it.

Today, we no longer care about the 51% attack, just like it is so certain that it will not happen. But a new order is here, the quantum attack and this will be used as a fud driver for so many years before we will get used to it as well.

[marto25]

The question is legitimate and deserves a more precise answer than "it can't happen" — because technically, it can.
On the numbers: The three largest mining pools (Foundry USA ~24%, AntPool ~18%, F2Pool ~13%) collectively hold around 55% of the global hashrate. The top five exceed 75%. So the mathematical threshold is reachable on paper.
Where the argument breaks down: Pools are not hashrate owners — they are coordinators. Every individual miner pointing their ASICs at a pool can redirect to a different stratum server within minutes. If Foundry or AntPool attempted anything shady, their contributed hashrate would evaporate before the attack could sustain itself. We've seen this dynamic play out historically when GHash.io briefly crossed 51% circa 2014 — miners self-corrected voluntarily.
The economic disincentive is real but not the full story: Most replies here correctly point out that attacking the network would crater BTC's price, destroying the attacker's own hardware investment and mining revenue. That logic holds for rational, profit-driven actors.
However — and this is worth taking seriously — a 51% attack does not require a profit motive. A sufficiently hostile state actor or ideologically motivated group could treat the cost as acceptable collateral for the goal of destruction or disruption. That vector is consistently underestimated in these discussions.
What the protocol does and does not protect you from: There is nothing in Bitcoin's consensus rules that physically prevents a 51% attack. What makes it impractical is a combination of economic game theory, decentralized hashrate ownership (not pool control), and the ability of honest miners and nodes to execute a rollback. The protocol defends against it indirectly — not by making it impossible, but by making it irrational for most conceivable actors.
Bottom line: Improbable for pool operators. Economically suicidal for profit-seeking actors. Non-trivial as a long-horizon concern if hashrate concentration continues trending upward or if security budgets shrink post-halving. Worth monitoring — not panicking about.

[hd49728]

I remember some years back that we were so concerned and scared of the 51% attack. There was fud about this attack, even when it was hypothetically impossible to happen, fud makers still found their ways to manipulate the market with it.

Today, we no longer care about the 51% attack, just like it is so certain that it will not happen. But a new order is here, the quantum attack and this will be used as a fud driver for so many years before we will get used to it as well.

51% attacks are possible to happen, and no attacks happen because people can get benefit from letting Bitcoin blockchain operates and Bitcoin adoption growth with time. It's how smart they are, early adopters can get profit, a lot of profit with time by being early Bitcoin miners or investors.

With smell of profit by actions they can do, they don't self destroy such get rich opportunities with stupid actions. Cost of doing attacks is huge while benefit is unknown, even zero, so why people have to do 51% attacks on Bitcoin blockchain.
https://blog.lopp.net/how-many-bitcoin-confirmations-is-enough/
https://jlopp.github.io/bitcoin-confirmation-risk-calculator/?ref=blog.lopp.net

[marrcelo]

I don't think a 51% attack is a real threat. Even if the biggest pools combined their hashrate, individual miners can switch pools whenever they want. The pools don't own the hashrate, the miners do. Financially the damage would be huge, if Bitcoin drops the losses would be so big that most of them would go bankrupt. I don't think they're stupid enough to do that.

[FP91G]

I believe quantum computers pose a more dangerous threat to Bitcoin than a 51% attack. A 51% attack requires significant investment and would be quickly detected. Quantum computing will allow private keys to be calculated from public keys. This will make it possible to surreptitiously empty old wallets. Without the transition to post-quantum security, BTC will lose investor confidence.

[Cookdata]

That is exactly what some people don't understand, those mining pools aren't owner of hashrate, it's just a pool and whoever the hashrate belong to can get out of the pool if they disagree.

I think we've had similar thing where a pool grow beyond 51% of total hashrate and a lot of people pulled out their hashrate to decentralize decade ago.

Whenever you see a pool becomes concentrated with hashrate, there is always something good the pool is doing to attract miners but miners are smart individuals, they aren't going to be so foolish to put Bitcoin at risk because of any benefit from any pool, it would even be like they are jeopardizing their source of income and destabilizing the network for a benefit that may not even cover their running cost, no sane miner in thief right sense will agree to 51% attack.

I believe quantum computers pose a more dangerous threat to Bitcoin than a 51% attack. A 51% attack requires significant investment and would be quickly detected. Quantum computing will allow private keys to be calculated from public keys. This will make it possible to surreptitiously empty old wallets. Without the transition to post-quantum security, BTC will lose investor confidence.

Good thing is 51% attack is avoidable, miners can leave a pool to join another pool to reduce hashrate from a pool but quantum computer is another large discussion entirely. Miners don't control private keys, when attacker get access to private key, they can spend any utxo and as long as the key is right, the transaction will be gladly accepted by miners node pools waiting on their mempool to be mine, that's worse than 51% catastrophe if you ask me but we will get pass that before it becomes a real threat.