It's not a realistic threat because Bitcoin network is very big in hash rate and attackers have to spent huge and expensive cost to own 51% of total hashrate or more to do attack.

Because Bitcoin network is decentralized from nodes to hashrate, if something looks suspicious, miners will change their mining pools. Communities like exchanges have bots to detect attacks and will halt their withdrawal and deposit so attackers will waste their money for attacks.

How many Bitcoin confirmations is enough?
https://jlopp.github.io/bitcoin-confirmation-risk-calculator/
https://web.archive.org/web/20181231045818/https://people.xiph.org/~greg/attack_success.html

https://howmanyconfs.com/

PoW 51% attack cost
https://www.crypto51.app/

This website:


says that for someone to operate a 51% attack for an hour to Bitcoin, it will cost them around $1.6M. This is prolly just an estimation and it could even be more. While it's gonna sound like a threat after looking at those projects that have been 51% attacked but it's highly unlikely to happen to Bitcoin. Whoever is gonna fund this much to just attack the network will cost them a lot and it might not be worth it because of how strong the network is and this is the beauty of Bitcoin's network and its security.

To be honest, I don't understand these values:
Name    Symbol    Market Cap    Algorithm    Hash Rate    1h Attack Cost    NiceHash-able
Bitcoin    BTC    $517.53 B    SHA-256           378,673 PH/s    $1,646,739             0%

Means that to attack Bitcoin network for 1h, it would cost 1 million, 6 hundred, forty six, 7 hundred and thirty nine dollars?


I would think this way:
Total hash power 378673PH/s

51% of Total hash power is ~195PH/s

Each S19xp Hybrid runs at ~257TH/s
Therefore we need  190000TH/s / 257TH/s = 760 miners
Each miner costs $8500, so, we need 8500*760 = $6460000 ~6.5 million dollars
Each miner uses 5350W/h, so, we need 5350 * 760 = 4066kW/h * 24h = 97584kW day
If electricity costs, let's say 6cents h, we need $5900000 day.

I'm not absolutely sure about my numbers but they seem ok to me. Anyone correct me if I'm wrong!
Now, the only question I don't know for sure how to answer is how much time would it take for this setup to take over the main chain of the other 49% of hashpower!

I just made a few fixes... If it's still too off, please tell me where!

No.

If you're attacking from within (using existing miners on the network) you have to buy up 51% of the miners on the network, which miners are not going to sell you. So no go there.

If you attacked from the outside (bringing new miners onto the network) you have to buy up 101% as many miners that are on the network.


Antminer S19 Pro is listed at $3230 from what I can see. Though I think sometimes miners go for much more, I was looking at miner prices a couple years ago and $3000 miners were selling for like $15k or something crazy. But let's just assume you could buy them for the actual list price.

At current hash rate it'd take about 3.3 million S19s to match the entire network hashrate in order to do a 51% attack, since you'd be doubling the hash rate. At list price, just buying the miners would cost about $10.5 billion. Now you have to pay for the infrastructure, both physical and electric, to run all these, and the workers to set them it all up. Also you have to get AC to cool down these facilities so the miners don't all melt down.

And then you gotta pay for the electricity. Looks like this would take about 10.725 million kilowatts just for the miners, not including AC and other electrical uses like lights, security stuff, etc. Assuming you can get $0.09/kw-h cost of electricity that's roughly a million dollars an hour, but more since we're not including all the other things you need electricity for in these buildings. Of likely you're not gonna be consuming over 10 million kilowatts in one location so you have to spread this all out, costing more. Ya gotta set it up somewhere so you gotta lease or buy land, hopefully land with buildings already on it so you don't have to build the buildings from scratch, so that land is gonna cost more.

So basically we're talking tens of billions of dollars in upfront costs, likely years of planning and setup, plus probably in total around $1.5 million every hour in electricity costs to do a 51% attack. Oh and of course you won't be able to get millions of miners at once, you'll have to order them over the course of several years, and you're gonna be competing with orders from all the people/companies already doing bitcoin mining, so you're not gonna be getting that list price on the miners anyway, so add a few more billions of dollars to the years-long setup.

Okay, now you've spent the past few years and tens of billions of dollars setting up all the infrastructure and buying all the miners and turning them on and you're ready for your attack! But wait, the hash rate has doubled in the meantime so you have to do the entire thing again....




Now, some people like to talk about mining pools colluding. But the thing they always fail to mention is that mining pools are, well, pools! They're made up of tons of different people. As soon as anyone got wind of several of the largest mining pools trying to attack bitcoin those mining pools would find themselves with far less than 51% of the network as the miners in those pools flee to other pools. So even in the situation that the largest mining pools wanted to kill their reputation and their business, and do this attack, it probably wouldn't even take an hour for the attack to end and their business to be destroyed.


The incentives of mining make it so nobody in the network would want to attack in, and the Bitcoin economy and security is so large now that it can't be attacked from outside. Bitcoin has for years now had global-level security, meaning that no entity or group of entities on earth could realistically engage in a 51% attack on it. Bitcoin is the most secure network in human history. Ain't nothing taking it down.

As others have mentioned, you would need north of $10 billion to at least achieve 51% of the mining hash rate. But I think this isn't the point. There are individuals, families, companies, banks, governments, and so on who have way more than $10 billion. They can afford to achieve that 51%. As a matter of fact, GHash.io once achieved 55% of Bitcoin’s hash rate. But the question is why would somebody invest so much money to attack Bitcoin? The key takeaways are that [1] it's not going to be profitable, so if it's for the money, it would be absurd, and then [2] it would only be temporary, quick; the takeover won't last forever, so if it's to destroy Bitcoin, it would also be absurd. So, what's the point? I think there's none.

You're calculating the cost of building a farm to attack the network, and you do that also wrong as Phil said
What that calculator does is simply taking the rent cost for 1th/a and multiplying by the needed hashrate, so no initial gear cost, no energy not anything else. Much like buying a car to go on a trip versus taking rental.

After all it's pretty simple, to get that hashrate you just have to rent it by paying the miners more than they are making but you will never be able to bribe mining pools with tens of exahashes to rent you that for one hour or two.

I've also read little about 51% attack and the possibility to that happening is vert weak because of the requirements in doing that, though the topic had been discussed on several occasions onbthe forum and the fact remains that as long as the bitcoin network and nodes work in consensus to the blockchain technology protocols, there will always be more difficulty may o having such attack on the bitcoin network.

Some threads on 51% attack you can read more on:

https://bt.irlbtc.com/view/655572.0
https://bt.irlbtc.com/view/208745.0

Control Bitcoin network will not be possible as long as the Bitcoin proof of work algorithm exists, and this attack or control of the network by the highest liquidity providers in the proof of stake algorithm is what has led to the debate of how centralization of the network could compromise the security and lead to a possible attack of control of the entire networks.

-In proof of work 51% control is not possible
-But in proof of stake the possibility is high.

In theory, a 51% attack is possible, but in practice it is impossible for many reasons, but the most important of them, as everyone pointed out, are economic reasons, because there is no economic benefit from this attack. It means that you are spending millions of dollars to steal some dollars. This is illogical.

This reminds me of firing cruise missiles, which cost a million dollars each, at the poor shacks in Afghanistan that are not worth a few dollars. This is useless.