<p>ViaBTC, a mining pool that favors Unlimited, <a href="https://i.redd.it/x9f7t3rhn4wy.png" rel="nofollow noreferrer">tweeted</a> “hashpower is law”.</p>

<p>Greg Maxwell (from the Core side) <a href="https://np.reddit.com/r/Bitcoin/comments/69t452/viabtc_comment_to_the_recent_segwit_pool/dh95hat/" rel="nofollow noreferrer">replied</a> “Bitcoin’s security works precisely because hash power is NOT law”.</p>

<p><strong>Introduction</strong></p>

<p>There are lots of people scared of the 51% attack, but in practice, thanks to some changes that have been implanted for years, performing this attack would be harmful to the attacker (in a game theory sense they lose), and not that much to the cryptocurrency user.</p>

<p><strong>How 51% used to be a problem</strong></p>

<p>The main danger that the 51% attack used to face was consistent mining by the 51%. Since everyone takes the longest chain as ground truth, the 51% could mine by itself and not publish any blocks, wait for their chain to be longer, and publish all the blocks, selecting all the transactions inside, and getting all the block rewards. </p>

<p><strong>What if they try</strong></p>

<p>Let's say some team of miners buy all the equipment and accomplishs to have more than 50% of the hashpower in a network, what can they do?</p>

<p>They could in theory perform the attack for a while, and they would get the rewards for mining, effectively fucking over the other miners.</p>

<p>What about the cryptocurrency users? the most damage they could do is to censor transactions for a while, but not consistently, since as soon as one of the other miners can at some point publish a block they could include the transaction.</p>

<p><strong>Can miners change the rules of the game?</strong></p>

<p>No, not even if they have 100% of the hashing power. Client-side validation means that many attempts at mischief that the miner might want to engage in are by default rejected, this is the main difference between blockchains and services like Paypal.</p>

<p><strong>What happens to the attackers</strong></p>

<p>It's important to note that this attack would be fairly easy to detect, not only that, but there are people that base their living on mining, so we would hear about it pretty quickly. 
As soon as this happens, users could decide to change move their assets, kick off malicious miners, even modify the protocol (the latter one would be the hardest). This would also cause FUD and the price would drop, making the miners, specially the malicious ones to lose money.</p>

<p><strong>Conclusions</strong></p>

<p>A 51% attack takes much more than a 51% of the network to execute nowadays, they barely hurt the end users (delay transactions), it would be easily detected,and it would hurt (economically) malicious miners the most.</p>

<p>Source miners power: <a href="https://vitalik.ca/general/2017/05/08/coordination_problems.html" rel="nofollow noreferrer">https://vitalik.ca/general/2017/05/08/coordination_problems.html</a></p>

CC BY-SA 4.0
2018-06-14T13:55:16.997Z
Great answer, but could you explain this a little more please? `Client-side validation means that many attempts at mischief that the miner might want to engage in are by default rejected, this is the main difference between blockchains and services like Paypal.`
VSO
CC BY-SA 4.0
2018-06-14T15:08:15.473Z
Bitcoin has a set of rules, every node checks that the blocks meet those rules, if any node changes the rules and starts behaving differently, they are essentially creating a different blockchain with a different set of rules.

For example, business that are running a regular non mining node, or the node that you could be running in your house will reject all their blocks.
Therefore if they change the rules they are effectively kicking themselves out of the network.

On the other hand, Paypal or Ripple could change the rules and you cannot do anything about it.
Enrique Alcazar
CC BY-SA 4.0
2018-06-14T15:13:48.777Z
To be fair, miners could implement themselves a soft-fork unilaterally (This has never happened and it would be an outrage) and restrict the rules, but never to expand or add them.
Enrique Alcazar
CC BY-SA 4.0
2018-06-14T18:38:15.577Z
You mention "kicking off" malicious miners, but without a POW change there is no way to do so. I'm also not sure about your assertion that *"A 51% attack takes much more than a 51% of the network to execute nowadays"*, what is your basis for that claim?
chytrik
CC BY-SA 4.0
2018-06-15T08:52:15.433Z
@chytrik There are ways to kick blocks produced from a malicious pool, just by kicking the initial block where they started cheating, all their work goes to waste (look up invalidate block in the [API calls](https://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list)). 

As for **"A 51% attack takes much more than a 51% of the network to execute nowadays"** You are right I shouldn't have said this without specifying it's my opinion and explaining myself, since I need more space I'll do it in the next comment.
Enrique Alcazar
CC BY-SA 4.0
2018-06-15T09:00:30.900Z
Why do you need much more than 51%? Let's say I want to double spend, and I have 51% of hashing power, in that case it would take me 51 blocks on average to catch up, but since I'm mining with only 51% of the total power, blocks would be slower to produce, the math adds up to 1000 minutes, in that time people would notice that blocks are slower, something is going on and block the malicious chain as soon as is broadcasted. With 80% of the power is still talking 33 minutes, people would again notice and just block the malicious chain. This is not the best course of action but a solution
Enrique Alcazar
CC BY-SA 4.0
2018-06-15T09:44:16.873Z
@EnriqueAlcazar there is not a way for the network to reach consensus on dropping the 'initial block' of the attack, so at best this would make the network fork, maybe many times. Also, this is not a way to stop an attack, only a way to react to one. A miner with 51% does not need to mine 51 blocks to catch up, I think you misunderstand the attack. At any given time, a miner with 51% can (with some probability) begin to continuously outrun the rest of the miners, thereby becoming the sole block producer. A miner can also submit blocks anonymously, making this harder to detect.
chytrik
CC BY-SA 4.0
2018-06-15T20:51:06.267Z
@chytrik detecting the initial block for the attack is really easy, and any node can decide to drop it, and this would generate a SOFT fork which would only not be followed purposely by the malicious operators, there is no need for everyone to drop the block, that's how a soft fork works. As for the 51% attack I was talking about the time it would take to substitute a single block to double spend, in your point about solo mining, that's even easier to detect, since has nothing to do with the submission of block, and the miners themselves, even being a minority, could fix that problem.
Enrique Alcazar
CC BY-SA 4.0
2018-06-15T20:57:07.713Z
Quick recap, if miners decide to attack they can either 1 censor/solo-mine: which would be really obvious since blocks would take more than double to get mined for a long time. 2 try a quick hidden attack to double spend, which right now would require more than 80% of the network to even have a chance. If they are ever caught, there are mechanisms to make the malicious miners lose all their rewards therefore having wasted a ton of money (around 5M in the case of a double spend with 51% of the network)
Enrique Alcazar
CC BY-SA 4.0
2018-06-15T21:15:16.913Z
@EnriqueAlcazar your understanding is slightly off, hard/soft fork distinction is not important here. Even if every node could identify and drop the right block (they can't, since they are independent), the attacker could simply restart the attack, ad infinitum. This could be effective in disrupting the network, since the attack can only be recognized in hindsight, and a miner cannot be banned due to the anonymous nature of block submission. Normal block variance routinely leads to a few blocks taking 20+ minutes in a row to be found, so a slower rate alone is no reason to suspect an attack.
chytrik
CC BY-SA 4.0
2018-06-15T21:26:02.623Z
This is getting childish, my understanding of a hard/soft fork is not wrong, and not only I explained that I didn't mean a solo mining but also explained why solo mining is not viable, and now you come with this?... They can easily detect the right block, is the first one different in the new chain... If the attacker keeps restarting the attack he would be losing 5M a day... Miners are not banned their blocks are... And finally blocks would take an average of 40+ plus for a full day... I explained all of this before, if you have anything interesting please contribute, if not, don't.
Enrique Alcazar
CC BY-SA 4.0
2018-06-15T21:30:51.690Z
Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/78951/discussion-between-chytrik-and-enrique-alcazar).
chytrik
CC BY-SA 4.0
2018-06-14T09:25:24.257Z
2018-06-14T15:17:44.947Z
2018-06-14T15:17:44.947Z
Enrique Alcazar
<p>Here is <a href="https://blockchain.info/pools" rel="noreferrer">Blockchain.info's chart</a> showing the current estimated distribution of the bitcoin network's hashrate.</p>

<p>Keep in mind: some pools are composed of many individual miners, so in the event of an attack, those individuals may simply redirect their hashpower to a different pool that is not involved in the attack.</p>

<p>In general, controlling the hashrate is not equivalent with 'controlling bitcoin'. If a single entity got control of 51% or more of the hashpower, then they could launch a 51% attack, meaning they could censor transactions. This is an existential threat to the network, but many developers have proposed countermeasures such as a POW change in the event such a thing ever happens. </p>

CC BY-SA 4.0
2018-06-13T17:44:01.570Z
2018-06-13T17:44:01.570Z
chytrik
<p>I would rather say 'dependent' but not 'controlled'. Meaning, China doesn't control Bitcoin on some governmental level, it's just because many miners are based in China and they have a direct impact on Bitcoin's growth. Sure it's a matter of personal opinion, so correct me if I'm wrong.</p>

CC BY-SA 4.0
2018-07-24T14:31:47.570Z
2018-07-24T14:31:47.570Z
richcoin
<p>Recently, the CEO of Ripple stated that more than 50% of the BitCoin miners are in China, therefore, were the Chinese 
government to interfere, they could control BitCoin (I assume via a 51% attack, I didn't check details).</p>

<p>"“I’ll tell you another story that is underreported, but worth paying attention to. Bitcoin is really controlled by China. There are four miners in China that control over 50% of Bitcoin,”"</p>

<p>Is it true that 4 Chinese miners can control all of BitCoin? </p>

<bitcoin-core><china>
Is BitCoin controlled by China?
VSO
# Is BitCoin controlled by China?

(Asked by: username_0 on 2018-06-13)

Recently, the CEO of Ripple stated that more than 50% of the BitCoin miners are in China, therefore, were the Chinese
government to interfere, they could control BitCoin (I assume via a 51% attack, I didn't check details).

"“I’ll tell you another story that is underreported, but worth paying attention to. Bitcoin is really controlled by China. There are four miners in China that control over 50% of Bitcoin,”"

Is it true that 4 Chinese miners can control all of BitCoin?

**Tags:** bitcoin-core, china


---

## 3 answers

### Answer by username_1 on 2018-06-14. Score: 2 | Accepted answer

ViaBTC, a mining pool that favors Unlimited, [tweeted](https://i.redd.it/x9f7t3rhn4wy.png) “hashpower is law”.

Greg Maxwell (from the Core side) [replied](https://np.reddit.com/r/Bitcoin/comments/69t452/viabtc_comment_to_the_recent_segwit_pool/dh95hat/) “Bitcoin’s security works precisely because hash power is NOT law”.

**Introduction**

There are lots of people scared of the 51% attack, but in practice, thanks to some changes that have been implanted for years, performing this attack would be harmful to the attacker (in a game theory sense they lose), and not that much to the cryptocurrency user.

**How 51% used to be a problem**

The main danger that the 51% attack used to face was consistent mining by the 51%. Since everyone takes the longest chain as ground truth, the 51% could mine by itself and not publish any blocks, wait for their chain to be longer, and publish all the blocks, selecting all the transactions inside, and getting all the block rewards.

**What if they try**

Let's say some team of miners buy all the equipment and accomplishs to have more than 50% of the hashpower in a network, what can they do?

They could in theory perform the attack for a while, and they would get the rewards for mining, effectively fucking over the other miners.

What about the cryptocurrency users? the most damage they could do is to censor transactions for a while, but not consistently, since as soon as one of the other miners can at some point publish a block they could include the transaction.

**Can miners change the rules of the game?**

No, not even if they have 100% of the hashing power. Client-side validation means that many attempts at mischief that the miner might want to engage in are by default rejected, this is the main difference between blockchains and services like Paypal.

**What happens to the attackers**

It's important to note that this attack would be fairly easy to detect, not only that, but there are people that base their living on mining, so we would hear about it pretty quickly.
As soon as this happens, users could decide to change move their assets, kick off malicious miners, even modify the protocol (the latter one would be the hardest). This would also cause FUD and the price would drop, making the miners, specially the malicious ones to lose money.

**Conclusions**

A 51% attack takes much more than a 51% of the network to execute nowadays, they barely hurt the end users (delay transactions), it would be easily detected,and it would hurt (economically) malicious miners the most.

Source miners power: <https://vitalik.ca/general/2017/05/08/coordination_problems.html>

> **Comments:**
> **username_0**: Great answer, but could you explain this a little more please? `Client-side validation means that many attempts at mischief that the miner might want to engage in are by default rejected, this is the main difference between blockchains and services like Paypal.`  
> **username_1**: Bitcoin has a set of rules, every node checks that the blocks meet those rules, if any node changes the rules and starts behaving differently, they are essentially creating a different blockchain with a different set of rules.  For example, business that are running a regular non mining node, or the node that you could be running in your house will reject all their blocks. Therefore if they change the rules they are effectively kicking themselves out of the network.  On the other hand, Paypal or Ripple could change the rules and you cannot do anything about it.  
> **username_1**: To be fair, miners could implement themselves a soft-fork unilaterally (This has never happened and it would be an outrage) and restrict the rules, but never to expand or add them.  
> **username_2**: You mention "kicking off" malicious miners, but without a POW change there is no way to do so. I'm also not sure about your assertion that *"A 51% attack takes much more than a 51% of the network to execute nowadays"*, what is your basis for that claim?  
> **username_1**: @username_2 There are ways to kick blocks produced from a malicious pool, just by kicking the initial block where they started cheating, all their work goes to waste (look up invalidate block in the [API calls](https://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list)).   As for **"A 51% attack takes much more than a 51% of the network to execute nowadays"** You are right I shouldn't have said this without specifying it's my opinion and explaining myself, since I need more space I'll do it in the next comment.  
> **username_1**: Why do you need much more than 51%? Let's say I want to double spend, and I have 51% of hashing power, in that case it would take me 51 blocks on average to catch up, but since I'm mining with only 51% of the total power, blocks would be slower to produce, the math adds up to 1000 minutes, in that time people would notice that blocks are slower, something is going on and block the malicious chain as soon as is broadcasted. With 80% of the power is still talking 33 minutes, people would again notice and just block the malicious chain. This is not the best course of action but a solution  
> **username_2**: @username_1 there is not a way for the network to reach consensus on dropping the 'initial block' of the attack, so at best this would make the network fork, maybe many times. Also, this is not a way to stop an attack, only a way to react to one. A miner with 51% does not need to mine 51 blocks to catch up, I think you misunderstand the attack. At any given time, a miner with 51% can (with some probability) begin to continuously outrun the rest of the miners, thereby becoming the sole block producer. A miner can also submit blocks anonymously, making this harder to detect.  
> **username_1**: @username_2 detecting the initial block for the attack is really easy, and any node can decide to drop it, and this would generate a SOFT fork which would only not be followed purposely by the malicious operators, there is no need for everyone to drop the block, that's how a soft fork works. As for the 51% attack I was talking about the time it would take to substitute a single block to double spend, in your point about solo mining, that's even easier to detect, since has nothing to do with the submission of block, and the miners themselves, even being a minority, could fix that problem.  
> **username_1**: Quick recap, if miners decide to attack they can either 1 censor/solo-mine: which would be really obvious since blocks would take more than double to get mined for a long time. 2 try a quick hidden attack to double spend, which right now would require more than 80% of the network to even have a chance. If they are ever caught, there are mechanisms to make the malicious miners lose all their rewards therefore having wasted a ton of money (around 5M in the case of a double spend with 51% of the network)  
> **username_2**: @username_1 your understanding is slightly off, hard/soft fork distinction is not important here. Even if every node could identify and drop the right block (they can't, since they are independent), the attacker could simply restart the attack, ad infinitum. This could be effective in disrupting the network, since the attack can only be recognized in hindsight, and a miner cannot be banned due to the anonymous nature of block submission. Normal block variance routinely leads to a few blocks taking 20+ minutes in a row to be found, so a slower rate alone is no reason to suspect an attack.  
> **username_1**: This is getting childish, my understanding of a hard/soft fork is not wrong, and not only I explained that I didn't mean a solo mining but also explained why solo mining is not viable, and now you come with this?... They can easily detect the right block, is the first one different in the new chain... If the attacker keeps restarting the attack he would be losing 5M a day... Miners are not banned their blocks are... And finally blocks would take an average of 40+ plus for a full day... I explained all of this before, if you have anything interesting please contribute, if not, don't.  
> **username_2**: Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/78951/discussion-between-username_2-and-username_1-username_1).  

---

### Answer by username_2 on 2018-06-13. Score: 6

Here is [Blockchain.info's chart](https://blockchain.info/pools) showing the current estimated distribution of the bitcoin network's hashrate.

Keep in mind: some pools are composed of many individual miners, so in the event of an attack, those individuals may simply redirect their hashpower to a different pool that is not involved in the attack.

In general, controlling the hashrate is not equivalent with 'controlling bitcoin'. If a single entity got control of 51% or more of the hashpower, then they could launch a 51% attack, meaning they could censor transactions. This is an existential threat to the network, but many developers have proposed countermeasures such as a POW change in the event such a thing ever happens.


---

### Answer by username_3 on 2018-07-24. Score: 1

I would rather say 'dependent' but not 'controlled'. Meaning, China doesn't control Bitcoin on some governmental level, it's just because many miners are based in China and they have a direct impact on Bitcoin's growth. Sure it's a matter of personal opinion, so correct me if I'm wrong.


---

