Is 51% attack on bitcoin just a myth or reality

[De Gramor]

While learning about bitcoin I came across somethings that are a bit challenging for so I thought of asking it here on the forum, I don’t know if I am mixing things up, if I am I will like you to correct me. So according to my readings it states In the history of bitcoin, we are fully aware that the blocks of the blockchain can be replaced by any miner with the support of high supply of mining power, which the acts is called 51% attack.
   To be more clear, the acts is just like rewriting a block of transactions under a blockchain and creating new transactions history, which is very difficult to achieve because the Mining works rates doubled, but it says to be achievable.
So I have been wondering at any point in history of bitcoin has any miner or group of miners  ever successfully achieved this goal, or have any one come closer in achieving it?

[Zaguru12]

So I have been wondering at any point in history of bitcoin has any miner or group of miners  ever successfully achieved this goal, or have any one come closer in achieving it?

There have never been this attack in the past and even in the even though it is not impossible to happen it is seriously improbable as the likelihood is very low.

The danger of even attempting this attack is even more than the advantages of getting it done, this is because you need to have at least the 51% power and the amount need to actually pull this up by one pool is so high that the reward is not worth it, possibly many pools can collude to do this but this can be noticed immediately and this pool will lose reputation while most honest miners will move out to other pools and will eventually end that pool power,

Looking at it, one thing that one can do with even 51% of the hash power is to double spend and that is even on y possible if you even have the private key or seed phrases of that bitcoin you wish to double spend, so it is utterly useless to do that. As for chain reorg yes you will have more proof of work and nodes will follow it but the blocks will definitely be valid ones, so if an attacker plans to have invalid blocks it will be definitely rejected by the nodes and nodes even if it has more proof of work and this is total a waste of power, so if you look at it the advantages of 51% attack is seriously not worth it and it is the reason why we haven’t experienced it and could possibly not experience it

[joniboini]

According to articles that I've found, Gash.io mining pool nearly got that 51% mining power in the past, but the community quickly moved away from that pool to balance the hashrate across different pools. The pool also put a limit of 40% hashrate power to avoid that. If we're talking outside of Bitcoin, we have many cases of a 51% attack. I think the cost to do the same for Bitcoin is so high that it's probably not feasible to do that now. CMIIW.

[philipma1957]

According to articles that I've found, Gash.io mining pool nearly got that 51% mining power in the past, but the community quickly moved away from that pool to balance the hashrate across different pools. The pool also put a limit of 40% hashrate power to avoid that. If we're talking outside of Bitcoin, we have many cases of a 51% attack. I think the cost to do the same for Bitcoin is so high that it's probably not feasible to do that now. CMIIW.

Back early cex.io had 52% but that in itself is not an issue since they just mined honestly and the adjustments were made to keep numbers under 50%.

It does not matter that a pool has 50 or even 60 percent if they mine honestly.

Also miners can switch to other pools.

What really matters if a company owns 60 or 70 % of all the gear then creates multiple huge mines and then mines illegally.

Can it be done yes it can.  IT IS COSTLY. As you need full control of about.

1100eh to match the current network

Which would be iffy to get it done.

So maybe 1400eh gets it done.

5 s21xps are 1400th = 1.4 ph

50 s21xps are 14000th =  14ph

500 s21xps are 140000th = 140ph

5000 s21xps are 1400000th = 1400ph = 1.4eh

50000 s21xps are 14000000th = 14000ph = 14eh

500000 s21xps are 140,000,000th = 140,000ph = 140eh almost there

5,000,000 s21xps are 1,400,000,000 th = 1,400,000 = 1400eh that is a big amount of gear.

And 5 million x 3.5kwatts= 17.5million kwatts of power per hour. Or 17500 megawatts of new power

That is about 3 Niagara Falls hydroplants of new power plants.

If you have 40 ft containers it is 16,700 of them

[Ambatman]

It does not matter that a pool has 50 or even 60 percent if they mine honestly.

Honesty doesn't change the fact on the type of governance such would cause
More centralization and could cause a chain reaction where people starts migrating from other pools to theirs
Because well they are 'honest'

So according to my readings it states In the history of bitcoin, we are fully aware that the blocks of the blockchain can be replaced by any miner with the support of high supply of mining power, which the acts is called 51% attack.

Owning 51% hash power isn't an attack. It's considered the minimum hash needed to wage an attack on the Blockchain.

[philipma1957]

It does not matter that a pool has 50 or even 60 percent if they mine honestly.

Honesty doesn't change the fact on the type of governance such would cause
More centralization and could cause a chain reaction where people starts migrating from other pools to theirs
Because well they are 'honest'

So according to my readings it states In the history of bitcoin, we are fully aware that the blocks of the blockchain can be replaced by any miner with the support of high supply of mining power, which the acts is called 51% attack.

Owning 51% hash power isn't an attack. It's considered the minimum hash needed to wage an attack on the Blockchain.

If there are multiple pools that are working ie at least 4 to 5 worldwide it will be simple to shift the 60% on pool a to pools b+c+d

The reality is having a lot of pools to pick say 25 or more would be nice but pools are costly to run and we do have 5 or 6 big ones to go to.

[Ambatman]

If there are multiple pools that are working ie at least 4 to 5 worldwide it will be simple to shift the 60% on pool a to pools b+c+d

The reality is having a lot of pools to pick say 25 or more would be nice but pools are costly to run and we do have 5 or 6 big ones to go to.

I'm not that versed in mining but from my little understanding
Pools join resources together and when a block is found
It is stared according to hash rate.
Owning 60% means you have an higher likelihood of winning the puzzle
And since they ain't malicious, they may become an attractive cake many want to taste from.

[De Gramor]

According to articles that I've found, Gash.io mining pool nearly got that 51% mining power in the past, but the community quickly moved away from that pool to balance the hashrate across different pools. The pool also put a limit of 40% hashrate power to avoid that. If we're talking outside of Bitcoin, we have many cases of a 51% attack. I think the cost to do the same for Bitcoin is so high that it's probably not feasible to do that now. CMIIW.

You are quite right though, I also came across something like this, where GHash.io mining pool exceeded 50% of the harsh rate in the year 2014. But unfortunately they could not make it happen because other pool boost up and make positive actions.
But in the history it says no other pool have try to or even reach that certain limit, I just read this I do not know maybe it true though.
It will be very difficult for a mining pool to make this possible movement.

[ABCbits]

So according to my readings it states In the history of bitcoin, we are fully aware that the blocks of the blockchain can be replaced by any miner with the support of high supply of mining power, which the acts is called 51% attack.

Owning 51% hash power isn't an attack. It's considered the minimum hash needed to wage an attack on the Blockchain.

To be exact, it's hashrate percentage needed to ensure success of re-org/double-spend attack. https://jlopp.github.io/bitcoin-confirmation-risk-calculator/ shows the chance based on hashrate percentage and depth of block.

But in the history it says no other pool have try to or even reach that certain limit, I just read this I do not know maybe it true though.

One of possible reason mining pool wouldn't do it because it'll make some Bitcoiner owner feel uneasy about misuse of the accumulated hashrate.

[odolvlobo]

There have been several altcoins that have been the victims of a 51% attack. Some coins were killed and some survived.

A notable attack that is commonly believed to be orchestrated by Luke-Jr in 2012 was against CoiledCoin: https://bitcointalk.org/index.php?topic=56675.msg675166

[Pmalek]

A 51% attack is theoretically possible but even if it's successful, it doesn't give the attacker absolute control of the blockchain. The attacker couldn't go around and steal random bitcoin from people. They could invalidate and doublespend their own transactions. For instance, the attacker sends you bitcoin, it confirms and you release money or goods to the attacker. The attacker with 51% or more hashrate could then invalidate that block and successfully cancel that transaction. He got what he wanted but you never got the promised bitcoin.

Doing this is very expensive, though. It makes more sense to mine honestly than dishonestly. The attacker would be interrupting the blockchain and preventing other people from using it normally. That would result in fear and FUD. The value of everyone's coins would drop to some degree, including those the attacker owns. They would be hurting themselves as well as others.

[ABCbits]

A notable attack that is commonly believed to be orchestrated by Luke-Jr in 2012 was against CoiledCoin: https://bitcointalk.org/index.php?topic=56675.msg675166

For more recent example, BTG (fork of BTC that aim to be GPU minable) also suffered from 51% attack few times in 2020. One of it caused $72K loss where the attacker perform double-spend on exchange.

[Satofan44]

It is a myth. It is never going to happen. This possibility is often used by shitcoiners who advocate for POS. A 51% attack in POS is much more realistic as it does not have any physical limitations. Stake is abstract, real world power is not. A 51% attack in a POS protocol takes complete control over the blockchain. A 51% attack in a POW protocol is a kamikaze level move that will make all miners obsolete. Temporary chaos, but you can't take control over Bitcoin this way.

For more recent example, BTG (fork of BTC that aim to be GPU minable) also suffered from 51% attack few times in 2020. One of it caused $72K loss where the attacker perform double-spend on exchange.

Of course it is possible in shitcoins. In terms of actual power expenditure, i.e., the actual security of a blockchain the dominance of Bitcoin is something like 99.9%. Coingecko would never show you that number though. 

[Pmalek]

It is a myth. It is never going to happen. This possibility is often used by shitcoiners who advocate for POS. A 51% attack in POS is much more realistic as it does not have any physical limitations. Stake is abstract, real world power is not. A 51% attack in a POS protocol takes complete control over the blockchain. A 51% attack in a POW protocol is a kamikaze level move that will make all miners obsolete. Temporary chaos, but you can't take control over Bitcoin this way.

I am not sure what exactly happened to Monero back in August. Some claim that there was a 51% attack against the blockchain that resulted in chain reorgs, but then the numbers also differ in the scope. Some say it was 6 blocks, other that more than 50 blocks got orphaned. One side is denying that any pool controlled more than 50% of the global hashrate, but the pool that allegedly did say they were successful. I haven't followed the story so I don't know if other miners were unable to mine blocks during the alleged attack or not and if there were significant doublespends.

Anyways, my point is that a popular PoW coin suffered or were at least close to suffering a 51% attack against its blockchain. Bitcoin is, of course, a different kind of beast from Monero, but still.

[Satofan44]

It is a myth. It is never going to happen. This possibility is often used by shitcoiners who advocate for POS. A 51% attack in POS is much more realistic as it does not have any physical limitations. Stake is abstract, real world power is not. A 51% attack in a POS protocol takes complete control over the blockchain. A 51% attack in a POW protocol is a kamikaze level move that will make all miners obsolete. Temporary chaos, but you can't take control over Bitcoin this way.

I am not sure what exactly happened to Monero back in August. Some claim that there was a 51% attack against the blockchain that resulted in chain reorgs, but then the numbers also differ in the scope. Some say it was 6 blocks, other that more than 50 blocks got orphaned. One side is denying that any pool controlled more than 50% of the global hashrate, but the pool that allegedly did say they were successful. I haven't followed the story so I don't know if other miners were unable to mine blocks during the alleged attack or not and if there were significant doublespends.

Anyways, my point is that a popular PoW coin suffered or were at least close to suffering a 51% attack against its blockchain. Bitcoin is, of course, a different kind of beast from Monero, but still.

It is likely that a small attack was possible but it is unknown if it was actually done, but you must understand one important difference. Having 51% hashrate =/= executing a 51% attack. Those are different things. For there to be a 51% attack the group that owns the 51% hashrate must execute at least 1 double spend against somebody. Orphaning blocks is not a sign of a successful 51% attack, there are other reasons for which this can happen such as selfish mining. AFAIK there is no proof that a 51% attack was successfully done against somebody or some entity in this case. Doing a double spend between your own wallets or those of your colleagues does not count. It has to be a market transaction of some short. In any case this is not legal, you can't with intent steal an asset or coin from somebody else especially not from established and large businesses such as Binance. I would expect a public entity that tries to do this to get quickly handled by the law. An anonymous attacker could get away with it but hiding all that hashrate (even if most of it is rented) is very difficult. In the case of Bitcoin it is impossible to anonymously utilize the amount of electrical power needed to execute this attack.

Anyways, my point is that a popular PoW coin suffered or were at least close to suffering a 51% attack against its blockchain. Bitcoin is, of course, a different kind of beast from Monero, but still.

Yes, that is why I wrote this in the second part of my post. In theory it is possible. For Bitcoin, in practice it is very unlikely. We have much bigger threats to worry about than this theoretical attack.

Of course it is possible in shitcoins. In terms of actual power expenditure, i.e., the actual security of a blockchain the dominance of Bitcoin is something like 99.9%. Coingecko would never show you that number though.  

[Phobos_Quake]

Satoshi Nakamoto once said:

"The system is secure as long as honest nodes collectively control more CPU power than any cooperating group of attacker nodes.  ...  If a greedy attacker is able to assemble more CPU power than all the honest nodes, he would have to choose between using it to defraud people by stealing back his payments, or using it to generate new coins. He ought to find it more profitable to play by the rules, such rules that favour him with more new coins than everyone else combined, than to undermine the system and the validity of his own wealth."

[Pmalek]

Satoshi Nakamoto once said:

"The system is secure as long as honest nodes collectively control more CPU power than any cooperating group of attacker nodes.  ...  If a greedy attacker is able to assemble more CPU power than all the honest nodes, he would have to choose between using it to defraud people by stealing back his payments, or using it to generate new coins. He ought to find it more profitable to play by the rules, such rules that favour him with more new coins than everyone else combined, than to undermine the system and the validity of his own wealth."

Yes, that's what I was talking about. It makes more sense to follow the rules and mine honestly than to do the opposite thing. Having so much power gives you an edge and an advantage over competitors, increasing your chances of finding more blocks than them. A party interested in celebrating Bitcoin's success and making money with it wouldn't want to abuse that. On the other hand, if someone has other goals, like hurting Bitcoin and trying to make it difficult for others to use it, they would need deep pockets to sustain an attack.

[ABCbits]

It is a myth. It is never going to happen. This possibility is often used by shitcoiners who advocate for POS. A 51% attack in POS is much more realistic as it does not have any physical limitations. Stake is abstract, real world power is not. A 51% attack in a POS protocol takes complete control over the blockchain. A 51% attack in a POW protocol is a kamikaze level move that will make all miners obsolete. Temporary chaos, but you can't take control over Bitcoin this way.

I am not sure what exactly happened to Monero back in August. Some claim that there was a 51% attack against the blockchain that resulted in chain reorgs, but then the numbers also differ in the scope. Some say it was 6 blocks, other that more than 50 blocks got orphaned. One side is denying that any pool controlled more than 50% of the global hashrate, but the pool that allegedly did say they were successful. I haven't followed the story so I don't know if other miners were unable to mine blocks during the alleged attack or not and if there were significant doublespends.

FYI 51% attack on Monero is FUD. BitMEX mentioned the actual hashrate was 33% or lower[1] while analysis from blockchain developer shows the actual hashrate was 35% or lower[2]. As stated on my previous post, it's possible to try re-org block with less than 51% hashrate. But the chance of success would be lower depending on hashrate percentage and block depth[3].

Anyways, my point is that a popular PoW coin suffered or were at least close to suffering a 51% attack against its blockchain. Bitcoin is, of course, a different kind of beast from Monero, but still.

Yeah, it's something i can agree. It's valuable lesson for community/developer of PoW coins.

[1] https://x.com/BitMEXResearch/status/1955254320305217726
[2] https://shai-deshe.gitbook.io/parallel-thoughts/proof-of-work/the-qubic-minority-report
[3] https://bitcointalk.org/index.php?topic=5561948.msg65907455#msg65907455

[Pmalek]

FYI 51% attack on Monero is FUD. BitMEX mentioned the actual hashrate was 33% or lower[1] while analysis from blockchain developer shows the actual hashrate was 35% or lower[2].

Both camps would have reasons to not tell the whole truth, so I chose not to pay attention to either block while it was happening. The pro-Monero side would have an incentive to downplay what happened to protect themselves and their investments. The anti-Monero said and the attackers have reasons to exaggerate what they did to seem more important and competent.

As stated on my previous post, it's possible to try re-org block with less than 51% hashrate. But the chance of success would be lower depending on hashrate percentage and block depth[3].

How may successful reorgs do you think there were in the alleged attack? As I said, I have read about 6 reorgs but also that there were over 50 orphaned blocks.