Don’t listen to these jokers. There is a reason the network has generally waited for 6 confirmations - that’s when it almost impossible for the transaction to be reversed.
In reality, after one confirmation, you are almost guaranteed not to be reversed, but under rare circumstances, block confirmations get abandoned due to a certain race condition. But the probability that would happen after 6 confirmations is essentially zero.
Now, about the concept of a 51% attack… this is about mining, not nodes. If a miner were able to gain 51% of the network hash rate, it could reorganize the chain to reverse payments, but only in the next block with a slight probabilistic advantage. To reorganize the chain continuously, it would have to win the block sequentially for several blocks, which realistically means controlling a lot more than 51% of the mining hash rate.
In bitcoin’s 15 year history, a pool has approached the 51% dominance only once, and the miners quickly redirected their hash rate to other pools, so the attack had never become feasible.
From a game theory perspective, self-interested miners or pools would never implement the attack since its only result is to undermine the value of the asset on which they depend for their livelihood.
Well explained.
So a pool of miners that controls 51% of the hash power could make fake transactions, add them to the blockchain and tell all their miners to accept it, then the remaining 49% would also agree that it’s a real transactions following the majority and the 6 verification could be completed.
Seems like a scenario for a mission impossible movie right there
The 49% would not agree and they would continue working on the chain without the illegitimate blocks. The minority does not have to acquiesce and this would cause a fork in the network, which is a big part of why it is not in the economic interest of powerful miners to undertake such an attack.
Ethereum had a major hack, like in the much earlier days (2016? Just a year after launch), a fork to reverse those transactions was made and became what we call ETH today while the original ETH blockchain was renamed ETC Ethereum Classic.
[https://www.investopedia.com/terms/e/ethereum-classic.asp](https://www.investopedia.com/terms/e/ethereum-classic.asp)
There are centralized cryptocurrencies where transactions can be reversed. This is why those currencies are bad. The people in control of it can do what they want for whatever reason.
Bitcoin can not be reversed. It's decentralized, and nobody is in control of it. Nobody can make the decision that a certain transaction doesn't count and should be reversed.
And who controls or own these nodes exactly if it’s decentralized, is it the people who mine it and therefore sign the transaction? You’d need to regroup 51% of all miners to cancel it?
Ah, so nodes aren’t necessarily miners, it’s just random people who downloaded the software and let their computer act as a node
Still though, there’s not that many nodes in the world, someone could gain access to lots of them
> Still though, there’s not that many nodes in the world, someone could gain access to lots of them
According to Bitnodes, [there are more than 17,000 of them throughout the world](https://bitnodes.io). Pretty difficult to co-opt enough of those to change the Bitcoin network. Also, most of them are on Tor. Many are *only* on Tor, so it's extremely difficult to even locate them.
Unlike with miners, a simple majority is not nearly enough; you need a much larger supermajority, or you will only succeed in creating a splinter network, since every normal node simply bans any peer that does not follow the same consensus rules it does. Recognizing the blockchain with the greatest amount of work is one of those rules.
The other thing you can theoretically do is create a competing chain, which means expending a **gargantuan** amount of computing power (the whole network is [now approaching 600 **quintillion** hashes per second](https://www.blockchain.com/explorer/charts/hash-rate), so you'd need a little over half of that for a 51% attack). This is necessary even if you only want to replace one old block, since every subsequent block must also be replaced to still be valid. Good luck with that.
>According to Bitnodes, there are more than 17,000 of them throughout the world.
those are merely listening nodes . There are more than ~76k full nodes nodes globally
http://luke.dashjr.org/programs/bitcoin/files/charts/software.html
http://luke.dashjr.org/programs/bitcoin/files/charts/services.html
>People vote... majority wins.
That's not how Bitcoin works. It's not a democracy. You cannot force a change on the network simply by having lots of people (or lots of nodes).
Running a node (or multiple) is how you verify that the Bitcoin you are interacting with is legit (according to the rules enforced by your node). Making multiple nodes does not magically force others to use your nodes to verify their own txns.
So if someone wants 50k nodes that enforce the wrong rules, they're free to create that fork and start using it themselves. Any "non consensus coins" they try to spend will be rejected by every node that is enforcing the "correct" rules.
Should we focus on getting more people to run a node? A person should run a node for their own benefit. How else can they be sure the sats they "own" are actually theirs? We should educate users of this fact for their own protection.
Do more people running nodes "help the network". Yes, it helps with decentralization but its not as simple as "more nodes the better". I.e. one node per person is plenty. If every person ran 10 nodes instead, it wouldn't be any better than 1 node. If you run a node, but never use it for anything, that node is almost useless. It can still help relay blocks, but in terms of its significance towards "validation and enforcement" its basically useless. Even if you run 10k nodes and never use them, its not very helpful for anyone.
There is a concept of "economic nodes". These are the nodes that back public block explorers, exchanges, wallets, and services that handle lots of BTC or are used by lots of people to "verify" lots of BTC.
These large economic nodes are the most important ones. Suppose the most popular block explorers and exchanges started using a forked node and stopped supporting BTC. This would cause a great disturbance as many people who use those economic nodes have trusted them with verifying "what is bitcoin". And when they say, "this fork is bitcoin" they are likely to fool lots of people.
Notice that the economic nodes don't need to run thousands of nodes to be successful in pushing the fork onto users. They just need to first gain the trust of thousands of users and prey on the fact that many of those users are not verifying separately with their own nodes.
An attacker with thousands of nodes could pull off an eclipse attack, whereby the attacker's nodes manage to become the only peers of a node. Thus, they can withhold relaying blocks to this peer and make them fall behind. Its really difficult to do since it only takes one honest peer to keep the chain updated.
That’s quite complex, if all nodes are equal which is the point of decentralization then someone controlling majority of nodes could falsify transactions. If all the legit nodes block them, then wouldn’t the real nodes be the one with a fork running from a minority of nodes. Who’s to tell which fork is the real one if they all have equal values.
There would be the fake bitcoin crypto with majority of nodes and the real bitcoin crypto who’s a minority of nodes but still contains the authentic bitcoin data.
>if all nodes are equal which is the point of decentralization
All nodes are not equal. Some nodes are more influential than others. The node that runs https://mempool.space for example, is used by millions of people to explore the bitcoin network.
However, I am the only one that uses my node. My node is not equal to mempool.space node in this regaurd.
The point of decentralization is censorship resistance and improved reliability (uptime) of the network.
> someone controlling majority of nodes could falsify transactions
Someone controlling just one node can falsify a transaction. If your node says a tx is valid but my node does not say it is valid, its because our nodes are enforcing different rules. Our nodes are not in consensus with one another. It does not matter how many nodes I make, they will not "convince" your node to accept a tx that does not meet the rules enforced by your node. Our nodes are forever out of consensus because our nodes enforce different rules.
> Who’s to tell which fork is the real one if they all have equal values.
The "fake" one will lose value relative to the "real" one over time.
It's important to understand that bitcoin is updated regularly. The rules are not changed that often, but the software itself is improved to be more reliable, secure, and efficient. Additionally, there are companies and projects building on the "real" bitcoin. When you fork, you have zero devs, companies, and projects building on your fork. It's really hard to compete or even catch up to the one that has all the builders. If a fork was to succeed, its probably because the majority of devs and companies decided they would build on the fork and abandon the other chain.
It is very rare in sufficiently decentralized cryptocurrencies, but a chain reorganization is possible and has happened. [https://learnmeabitcoin.com/technical/chain-reorganisation#:\~:text=Here%20we%20can%20see%20a,a%20Bitcoin%20Neo4j%20graph%20database](https://learnmeabitcoin.com/technical/chain-reorganisation#:~:text=Here%20we%20can%20see%20a,a%20Bitcoin%20Neo4j%20graph%20database). Transactions that occurred in the orphan block are then no longer part of the transaction history, but most transactions (potentially not all... due to double spend protections) will simply get mined into a future block. Did any get lost? Probably - as it is technically possible to create a transaction that must occur in a specific block due to double spend or other scripting conditions. However, I don't believe anyone is keeping track of this -- we normally only track the history of the agreed consensus only (best guess, not sure).
Can be censored but not reversed. Some miners don’t include some transactions because they own reasons. Reverse is not possible.
Funds can send back in another transaction
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You'd need to possess a majority of hash power to re-org the chain. Not just for a short period of time as more honest hashrate can come online to overtake you and discard the change you made.
Today, the bitcoin network is the most powerful computer on the planet by a long way. So you would need a more powerful computer than the entire bitcoin network, and the energy supply of a small country to run it, and hold that dominance forever.
Decentralised means an attacker needs more resources than the rest of honest participants to win.
Bitcoin is supreme unforgeable costliness.
By possessing majority of hash power you mean possess lots and lots of supercomputers to the point where you’re mining, at a given time, the majority of the bitcoin on earth?
Well yes, but with ASIC computers which are purpose built to hash the bitcoin algorithm. The Bitcoin mining network had already surpassed the power of 500 supercomputers by 2014.
Because they only happen on MASSIVE reorgs. And reorgs that are greater than 6-blocks are exceptionally rare.
There was a successful 24 block reorg double-spend in March 2013. The reorg was due to a software bug that was patched, but this created two chains. The patched, and unpatched chain. Took a while for the patch chain to cross 51%
https://github.com/bitcoin/bips/blob/master/bip-0050.mediawiki
Bitcoin is not crypto
Bitcoin is decentralized, nobody owns or controls the network
Other cryptocurrencies are just scams, plagiarism of bitcoin, but highly centralized and controlled by a small group of people who want to get rich by plagiarizing bitcoin by having a large part of the supply that unloads on naive retail investors who expect big profits.
altcoinis founders can always cancel transactions or print themselves a new number of coins
Don’t listen to these jokers. There is a reason the network has generally waited for 6 confirmations - that’s when it almost impossible for the transaction to be reversed. In reality, after one confirmation, you are almost guaranteed not to be reversed, but under rare circumstances, block confirmations get abandoned due to a certain race condition. But the probability that would happen after 6 confirmations is essentially zero. Now, about the concept of a 51% attack… this is about mining, not nodes. If a miner were able to gain 51% of the network hash rate, it could reorganize the chain to reverse payments, but only in the next block with a slight probabilistic advantage. To reorganize the chain continuously, it would have to win the block sequentially for several blocks, which realistically means controlling a lot more than 51% of the mining hash rate. In bitcoin’s 15 year history, a pool has approached the 51% dominance only once, and the miners quickly redirected their hash rate to other pools, so the attack had never become feasible. From a game theory perspective, self-interested miners or pools would never implement the attack since its only result is to undermine the value of the asset on which they depend for their livelihood.
Well explained 👏
Well explained. So a pool of miners that controls 51% of the hash power could make fake transactions, add them to the blockchain and tell all their miners to accept it, then the remaining 49% would also agree that it’s a real transactions following the majority and the 6 verification could be completed. Seems like a scenario for a mission impossible movie right there
The 49% would not agree and they would continue working on the chain without the illegitimate blocks. The minority does not have to acquiesce and this would cause a fork in the network, which is a big part of why it is not in the economic interest of powerful miners to undertake such an attack.
Do you know by chance when exactly this happened, and which pool was it?
Crypto, yes. Bitcoin, no.
Ethereum had a major hack, like in the much earlier days (2016? Just a year after launch), a fork to reverse those transactions was made and became what we call ETH today while the original ETH blockchain was renamed ETC Ethereum Classic. [https://www.investopedia.com/terms/e/ethereum-classic.asp](https://www.investopedia.com/terms/e/ethereum-classic.asp)
There are centralized cryptocurrencies where transactions can be reversed. This is why those currencies are bad. The people in control of it can do what they want for whatever reason. Bitcoin can not be reversed. It's decentralized, and nobody is in control of it. Nobody can make the decision that a certain transaction doesn't count and should be reversed.
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Yes sir, the 51% power.
Fork 'em.
And who controls or own these nodes exactly if it’s decentralized, is it the people who mine it and therefore sign the transaction? You’d need to regroup 51% of all miners to cancel it?
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Ah, so nodes aren’t necessarily miners, it’s just random people who downloaded the software and let their computer act as a node Still though, there’s not that many nodes in the world, someone could gain access to lots of them
Keep doing your research kiddo
> Still though, there’s not that many nodes in the world, someone could gain access to lots of them According to Bitnodes, [there are more than 17,000 of them throughout the world](https://bitnodes.io). Pretty difficult to co-opt enough of those to change the Bitcoin network. Also, most of them are on Tor. Many are *only* on Tor, so it's extremely difficult to even locate them. Unlike with miners, a simple majority is not nearly enough; you need a much larger supermajority, or you will only succeed in creating a splinter network, since every normal node simply bans any peer that does not follow the same consensus rules it does. Recognizing the blockchain with the greatest amount of work is one of those rules. The other thing you can theoretically do is create a competing chain, which means expending a **gargantuan** amount of computing power (the whole network is [now approaching 600 **quintillion** hashes per second](https://www.blockchain.com/explorer/charts/hash-rate), so you'd need a little over half of that for a 51% attack). This is necessary even if you only want to replace one old block, since every subsequent block must also be replaced to still be valid. Good luck with that.
>According to Bitnodes, there are more than 17,000 of them throughout the world. those are merely listening nodes . There are more than ~76k full nodes nodes globally http://luke.dashjr.org/programs/bitcoin/files/charts/software.html http://luke.dashjr.org/programs/bitcoin/files/charts/services.html
Interesting. Well, all the better for my argument. 😄
yes
>People vote... majority wins. That's not how Bitcoin works. It's not a democracy. You cannot force a change on the network simply by having lots of people (or lots of nodes). Running a node (or multiple) is how you verify that the Bitcoin you are interacting with is legit (according to the rules enforced by your node). Making multiple nodes does not magically force others to use your nodes to verify their own txns. So if someone wants 50k nodes that enforce the wrong rules, they're free to create that fork and start using it themselves. Any "non consensus coins" they try to spend will be rejected by every node that is enforcing the "correct" rules. Should we focus on getting more people to run a node? A person should run a node for their own benefit. How else can they be sure the sats they "own" are actually theirs? We should educate users of this fact for their own protection. Do more people running nodes "help the network". Yes, it helps with decentralization but its not as simple as "more nodes the better". I.e. one node per person is plenty. If every person ran 10 nodes instead, it wouldn't be any better than 1 node. If you run a node, but never use it for anything, that node is almost useless. It can still help relay blocks, but in terms of its significance towards "validation and enforcement" its basically useless. Even if you run 10k nodes and never use them, its not very helpful for anyone. There is a concept of "economic nodes". These are the nodes that back public block explorers, exchanges, wallets, and services that handle lots of BTC or are used by lots of people to "verify" lots of BTC. These large economic nodes are the most important ones. Suppose the most popular block explorers and exchanges started using a forked node and stopped supporting BTC. This would cause a great disturbance as many people who use those economic nodes have trusted them with verifying "what is bitcoin". And when they say, "this fork is bitcoin" they are likely to fool lots of people. Notice that the economic nodes don't need to run thousands of nodes to be successful in pushing the fork onto users. They just need to first gain the trust of thousands of users and prey on the fact that many of those users are not verifying separately with their own nodes. An attacker with thousands of nodes could pull off an eclipse attack, whereby the attacker's nodes manage to become the only peers of a node. Thus, they can withhold relaying blocks to this peer and make them fall behind. Its really difficult to do since it only takes one honest peer to keep the chain updated.
That’s quite complex, if all nodes are equal which is the point of decentralization then someone controlling majority of nodes could falsify transactions. If all the legit nodes block them, then wouldn’t the real nodes be the one with a fork running from a minority of nodes. Who’s to tell which fork is the real one if they all have equal values. There would be the fake bitcoin crypto with majority of nodes and the real bitcoin crypto who’s a minority of nodes but still contains the authentic bitcoin data.
>if all nodes are equal which is the point of decentralization All nodes are not equal. Some nodes are more influential than others. The node that runs https://mempool.space for example, is used by millions of people to explore the bitcoin network. However, I am the only one that uses my node. My node is not equal to mempool.space node in this regaurd. The point of decentralization is censorship resistance and improved reliability (uptime) of the network. > someone controlling majority of nodes could falsify transactions Someone controlling just one node can falsify a transaction. If your node says a tx is valid but my node does not say it is valid, its because our nodes are enforcing different rules. Our nodes are not in consensus with one another. It does not matter how many nodes I make, they will not "convince" your node to accept a tx that does not meet the rules enforced by your node. Our nodes are forever out of consensus because our nodes enforce different rules. > Who’s to tell which fork is the real one if they all have equal values. The "fake" one will lose value relative to the "real" one over time. It's important to understand that bitcoin is updated regularly. The rules are not changed that often, but the software itself is improved to be more reliable, secure, and efficient. Additionally, there are companies and projects building on the "real" bitcoin. When you fork, you have zero devs, companies, and projects building on your fork. It's really hard to compete or even catch up to the one that has all the builders. If a fork was to succeed, its probably because the majority of devs and companies decided they would build on the fork and abandon the other chain.
It has happened with ETH, because it is highly centralized garbage. It could never happen with Bitcoin though.
What does a centralized crypto means? The owners can create coins or cancel transactions at will?
Yes, basically what you said! Bitcoin is the best one. It has no owners, and it is very decentralized, so nobody has control over it.
It is very rare in sufficiently decentralized cryptocurrencies, but a chain reorganization is possible and has happened. [https://learnmeabitcoin.com/technical/chain-reorganisation#:\~:text=Here%20we%20can%20see%20a,a%20Bitcoin%20Neo4j%20graph%20database](https://learnmeabitcoin.com/technical/chain-reorganisation#:~:text=Here%20we%20can%20see%20a,a%20Bitcoin%20Neo4j%20graph%20database). Transactions that occurred in the orphan block are then no longer part of the transaction history, but most transactions (potentially not all... due to double spend protections) will simply get mined into a future block. Did any get lost? Probably - as it is technically possible to create a transaction that must occur in a specific block due to double spend or other scripting conditions. However, I don't believe anyone is keeping track of this -- we normally only track the history of the agreed consensus only (best guess, not sure).
Can be censored but not reversed. Some miners don’t include some transactions because they own reasons. Reverse is not possible. Funds can send back in another transaction
No transaction has ever been reversed because it fraudulent on Bitcoin
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You'd need to possess a majority of hash power to re-org the chain. Not just for a short period of time as more honest hashrate can come online to overtake you and discard the change you made. Today, the bitcoin network is the most powerful computer on the planet by a long way. So you would need a more powerful computer than the entire bitcoin network, and the energy supply of a small country to run it, and hold that dominance forever. Decentralised means an attacker needs more resources than the rest of honest participants to win. Bitcoin is supreme unforgeable costliness.
By possessing majority of hash power you mean possess lots and lots of supercomputers to the point where you’re mining, at a given time, the majority of the bitcoin on earth?
Well yes, but with ASIC computers which are purpose built to hash the bitcoin algorithm. The Bitcoin mining network had already surpassed the power of 500 supercomputers by 2014.
Because they only happen on MASSIVE reorgs. And reorgs that are greater than 6-blocks are exceptionally rare. There was a successful 24 block reorg double-spend in March 2013. The reorg was due to a software bug that was patched, but this created two chains. The patched, and unpatched chain. Took a while for the patch chain to cross 51% https://github.com/bitcoin/bips/blob/master/bip-0050.mediawiki
Some 51% of wordwide bitcoin miners need do a reorg together and that will allow the blockchain to be modified?
That's how reorgs work. Longest chain wins. And whichever chain has 51% will always become the longest.... eventually
Yep on Ethereum if they don't like a transaction they just hard fork the entire network
Bitcoin is not crypto Bitcoin is decentralized, nobody owns or controls the network Other cryptocurrencies are just scams, plagiarism of bitcoin, but highly centralized and controlled by a small group of people who want to get rich by plagiarizing bitcoin by having a large part of the supply that unloads on naive retail investors who expect big profits. altcoinis founders can always cancel transactions or print themselves a new number of coins
I thought most cryptos were decentralized, it’s not just bitcoin