4 ms·

On the growing risk of the 51% attack against BCash

60 points by yourrng 9y ago

em3rgent0rdr 9y ago
tl;dr: younger coins have fewer miners, so they are more susceptible to 51% attack. In particular BCash has same hash function as BTC, so those BTC miners could easily switch into mining BCash, and so is even more at risk.
- oh_sigh 9y ago
  It would incur a huge opportunity cost for them to switch over, especially because they would tank bcash by doing it.
  - em3rgent0rdr 9y ago
    Yes it would. This article is surprisingly ignorant of past discussion of the %51 attack.
    - moduspol 9y ago
      It also fails to account for the possibility that Bitcoin Cash becomes more valuable, and then Bitcoin is the "vulnerable" chain. It also doesn't mention the name of the author, and the HN user who posted this was created two hours ago. HNers should understand there is a huge political divide in the Bitcoin community right now on this very subject. Anonymous write-ups of known attack vectors framed as genuine warnings are nothing more than unsubstantiated fear, uncertainty, and doubt.
      - deleted 9y ago
        [deleted]
ringaroundthetx 9y ago
The was a long winded explanation of a 51% attack lol. Was the author just talking about hashrate switching? Any solutions for exchanges or merchants such as just increasing the confirmations required? Any interest in bitcoin cash changing it's algorithm?
- milcron 9y ago
  > Any interest in bitcoin cash changing it's algorithm? I doubt it. One of the reasons BCH hardforked was so large mining pools could continue to take advantage of Asicboost, a patented approach to Bitcoin hashing that provides a 20-30% speedup. Asicboost is essentially taking advantage of a flaw in the original Bitcoin algorithm which leads to slightly predictable hashes. Segwit fixed this problem, nullifying their patented advantage. All of the vocal BCH supporters are involved with large sha256 mining pools. I think it's very unlikely that they'll elect to change algorthms.
aviv 9y ago
BCash is a scam to convert as much of their scam coin as possible to Bitcoin over time.
- mnr 9y ago
  [citation needed]
- godzillabrennus 9y ago
  BCash is a fork of bitcoin that appears to offer lower fees for transactions.
lurr 9y ago
> But I’ll try to explain everything technically and stay objective You failed inside of 3 paragraphs.
- moduspol 9y ago
  The headline used the term "BCash." It'd be tough to have an objective post by someone about "BCore," too.
stale2002 9y ago
OK, this is describing a 51% attack. And who would engage in this 51% attack? The miners? The miners are one of the biggest groups that SUPPORT Bitcoin Cash, so I find it unlikely that they would spend millions attacking it. Anyway. It matters not. The people that want Bitcoin to be a settlement layer are free to spend 50$ per transaction to use Bitcoin, and those of us who want to use it as an actual peer to peer electronic currency will use Bitcoin Cash. Everyone wins. It doesn't really matter what is the "real" Bitcoin.
- mplewis 9y ago
  Anyone who's mining Bitcoin could switch to Bitcoin Cash and work to perform a 51% attack. > BCash shares hashing algorithm with Bitcoin. That means any hashing power on the Bitcoin network can work on BCash network. And there is typically 10 times more miners mining on BTC, than on BCH because of the difference in the price and minning fees.
  - stale2002 9y ago
    And which miner SPECIFICALLY would do that? There are only like 7 major mining pools. Which of those 7 do you think would do an attack? The miners were the ones who helped create Bitcoin Cash. Why would they attack it? The miners are the largest supporters of big blocks, so it make no sense that they would attack the thing that they helped launch. Also, people don't seem to realize that it is already possible to do a ~20 percent selfish mining attack. And yet we don't see THAT happening... These attacks aren't realistic in practice because it would be immediately obvious that something is happening, and the miners would lose all their money as Bitcoin crashes.
    - yourrng 9y ago
      Let me count some scenarios: * a miner losing its share in the competitive game could make a one last money grab before its hardware is obsolete * BCash backing miners losing confidence in success of BCH could just damage the whole space, for revenge or and profit * complete outsider like an angry government could try to disrupt the space to ban all crypto or at least heavily regulate it / buy some time
ErikAugust 9y ago
Is it possible it's already happened? I have no idea what the mining breakdown looks like - but I'd imagine it's only a couple players mining BCH. I'd think you could rewrite the chain at will pretty much.
- VMG 9y ago
  We would see two chains forking of a shared block with a significant length (~10). Unless you count Bitcoin Clashic[1], there's no proof of that http://bitcoinclashic.org/ http://bitcoinclashic.org/
bishopknight 9y ago
Not happening. ANT Pool has a huge investment in Bitcoin Cash and would swoop in with mining power to protect their investment.
- yourrng 9y ago
  Please re-read the post, because you don't understand. The 51% attack is carried in secret. Noone has any way to know if it is happening until the longer chain is published. And after that, it's too late already. Someone could try to catch up with (not anymore secret) longest chain, but the damage has been done - the state of the network has already changed. Actually switching it back is only adding salt to the wound. Noone would trust that coin again anyway, and it is worthless to try to rescue it. AntPool is busy mining Bitcoin, because it pays better: https://blockchain.info/pools https://blockchain.info/pools so it can't constantly police BCash chain by over-provisioning it.
  - deleted 9y ago
    [deleted]
- VMG 9y ago
  How would they protect it after a double spend occurred?
toomim 9y ago
A 51% attack only allows you to (1) censor transactions for a short time, and (2) double-spend. The first part is a mild nuisance. The second one can be retaliated against off-chain, which puts the attacker (who must be a large entity) at great risk in the real world.
- VMG 9y ago
  > The second one can be retaliated against off-chain. What do you mean?
  - chc 9y ago
    I believe it means that the recipient of the double-spent transaction can sue you or send goons after you just like they would someone who defrauded them without using cryptocurrency.
    - VMG 9y ago
      How would you determine the culprit? You can't even prove that there was an intent to roll back a particular transaction.
      - cperciva 9y ago
        No, but you can show that there was an intention to double-spend coins.
  - gizmo686 9y ago
    If you do a double spend attack of any significance, the other party will notice. Unless you are doing something completely anonymous, the other party will also know who you are and be able to pursue other remedies (eg. sue you for fraud).
    - VMG 9y ago
      If double-spend detection rather than prevention was enough, you could build a much cheaper and more efficient payment system than Bitcoin. What makes Bitcoin interesting is the fact that you don't have to resort to the legal system for final arbitration.
ubu7737 9y ago
The spectrum is really marvelous. It's amazing to see how many different kinds of people, with many different motivations, will waste their time on speculative crypto-coins.
jVinc 9y ago
I like the math and theory on this. But really why would someone who's making millions on the status quo risk tanking the market for a one time gain? Seems unlikely.
- yourrng 9y ago
  You don't have to risk anything. If the trend continues, at some point one would be able to rent the mining power required. On top of it, if you are a small miner, and you can't afford capital investments required to keep up with latest mining hardware, while loosing market share, you can use your soon-osolete hardware to make a one last buck. A big buck this time.
  - xiphias 9y ago
    At this point 5-10% of hash rate is a huge cost in mining hardware (maybe hundreds of millions). Also the hardware improvements already slowed down a lot. Antminer S9 is more than a year old. I wouldn't risk decreasing the BTC price by attacking BCH.
- soared 9y ago
  Any organization/individual/government who has enough money that they aren't interested in cashing out and is also interested in medium/large scale economic disruption. China, Russia, UAE, USA, sci-fi terrorists, evil villains, illuminati etc. (I'm only mostly joking)
- SAI_Peregrinus 9y ago
  One possibility would be to keep up and coming competitor currencies from gaining a foothold. The big ASIC mining farms bitcoin has won't work with some of the smaller currencies. The organizations running them have a lot of money, and don't necessarily want to see competition from less centralized mining. Destroying trust in a currency by executing a double spend attack on it could be one way to prevent that.
omarforgotpwd 9y ago
Who is seriously going to try and execute a 51% attack? It would be so incredibly expensive, you would have to keep spending more as people added hash power to shut you out, and most importantly if your attack worked you would instantly undermine the security of the blockchain making all the currency you've stolen worthless!
deftnerd 9y ago
I can't take any criticisms against Bitcoin Cash seriously when the authors knowingly refer to it as BCash. It's not just a shortening of the name, it's part of a concerted effort by detractors to distance the chain from the Bitcoin legacy. Any author that purposefully uses the term BCash is, on the face, incapable of being objective because they're advertising that they're detractors already. The Bitcoin Core (no on-chain scaling at any cost!) crowd asked the on-chain scaling fans to "fork off and leave". Now that the coin is doing very well in terms of market value and especially in growing merchant adoption, they're desperate to push the narrative that it's a scam or dangerous or can't be taken seriously. They know that if they can't destroy Bitcoin Cash now, it has a reasonable chance of eventually overtaking the legacy Bitcoin network in every important respect.
- MintPattern 9y ago
  It’s called bcash in hopes that too many newbies won’t go deposit bitcoin into a “bitcoin cash” address and sadly lose it all.
  - zepolen 9y ago
    Why would he lose it?
  - toomim 9y ago
    Again, this is a myth spread by people trying to tarnish Bitcoin Cash's image. The truth is that the money can't be lost. If you have the Bitcoin Cash private keys for the deposit address, you have the Bitcoin Core private keys on the Core chain. All that happens is that someone accidentally receives Bitcoin Core instead of Cash.
    - deleted 9y ago
      [deleted]
    - MintPattern 9y ago
      A lot of newbies put everything on an online exchange and don't bother with handling private keys. I haven't found a single exchange yet where you control the private keys. The public keys on exchanges I've seen are different for Bitcoin Cash and Bitcoin. Also, can you imagine the end result of paying for a good or service that accepts Bitcoin with Bcash?
JepZ 9y ago
When the BTC-BCH split happend I didn't really understand what everybody was talking about transaction fees. So after BTC continued to rise the past months and we have transaction fees >20$ I understand what was discussed earlier this year. I just wonder why the core devs were against increasing the blocksize. Yes, it would not have been a solution for the next 20 years, but at least it would have left the fees at a place where BTC was still suitable for the everyday use until other solutions could be established.
- moduspol 9y ago
  I think they have valid arguments for keeping smaller blocks, but this FUD is getting ridiculous. This very post has no new ideas, has no listed author, and is posted by a two hour old user account. It's not even about discussing what's best for Bitcoin any more.
- notsrg 9y ago
  Increasing the blocksize increases centralization at a time where miners have unprecedented power.
  - JepZ 9y ago
    How does it increase centralization and why have miners more power than 5 years ago? (Just because the value increased? Do they have more influence to the community?) Could you pleace elaborate on that?
    - exit 9y ago
      it increases centralisation because large blocks do not propagate as easily, and therefore encourage mining co-location
- fizzbuzzbazz3 9y ago
  There are many technical reasons, but I'll respond differently. Bitcoin is not a business-coin. Bitcoin is an idea-coin. It was never about the price, the price is just a side-effect. For many early adopters and developers, Bitcoin is about changing the world. Not in a marketing bullshit-world, but in a real way. We really believe that the world would be a better place if we've put a stop to government and banks monopoly on controlling the money. You may disagree, and it's fine. We believe in it, and we want to have the most secure, uncensorable and attack-resistant value transferring network. If it takes $30 to pay to transfer on such network, so be it. Increasing the block size compromises on that property, so we are not willing to do it, even though it's painful for everyone. We will wait. We have credit cards, we PayPal, and we can use altcoins before we get there. The price will rise and fall, users will come and go. We held at $1, we held at $10, we held at $20k, and we will hold at $10 again if it's required. We will get our layer 2 solution and get both our uncensorable, government-resistant network and instant cheap micropayments. That's why most of us dumped BCH coins without thinking twice. What most other coins are (not all!) is a business-coin. They are mostly pointless. Ethereum could be really a centralized smart-contracts platform run by Google or Amazon, and noone would care much. Actually, I believe that's how ETH is going to end. I believe Amazon engineers are working on it already. Because who cares about centralization or censorship resistance, if the main use case is breading virtual cats? No government will be interested in censoring that. What BCash is, is a scam coin. It's all about ASICBOOST and Roger Ver's hurt pride. He would like to be a pope of Bitcoin, but noone really cares about him. Except for a talent for scamming people for his own gain, he is noone.

60 points by yourrng 9y ago

tl;dr: younger coins have fewer miners, so they are more susceptible to 51% attack. In particular BCash has same hash function as BTC, so those BTC miners could easily switch into mining BCash, and so is even more at risk.

oh_sigh 9y ago
It would incur a huge opportunity cost for them to switch over, especially because they would tank bcash by doing it.
- em3rgent0rdr 9y ago
  Yes it would. This article is surprisingly ignorant of past discussion of the %51 attack.
  - moduspol 9y ago
    It also fails to account for the possibility that Bitcoin Cash becomes more valuable, and then Bitcoin is the "vulnerable" chain. It also doesn't mention the name of the author, and the HN user who posted this was created two hours ago. HNers should understand there is a huge political divide in the Bitcoin community right now on this very subject. Anonymous write-ups of known attack vectors framed as genuine warnings are nothing more than unsubstantiated fear, uncertainty, and doubt.
    - deleted 9y ago
      [deleted]

ringaroundthetx 9y ago

The was a long winded explanation of a 51% attack lol. Was the author just talking about hashrate switching? Any solutions for exchanges or merchants such as just increasing the confirmations required? Any interest in bitcoin cash changing it's algorithm?

milcron 9y ago
> Any interest in bitcoin cash changing it's algorithm? I doubt it. One of the reasons BCH hardforked was so large mining pools could continue to take advantage of Asicboost, a patented approach to Bitcoin hashing that provides a 20-30% speedup. Asicboost is essentially taking advantage of a flaw in the original Bitcoin algorithm which leads to slightly predictable hashes. Segwit fixed this problem, nullifying their patented advantage. All of the vocal BCH supporters are involved with large sha256 mining pools. I think it's very unlikely that they'll elect to change algorthms.

aviv 9y ago

BCash is a scam to convert as much of their scam coin as possible to Bitcoin over time.

mnr 9y ago
[citation needed]
godzillabrennus 9y ago
BCash is a fork of bitcoin that appears to offer lower fees for transactions.

lurr 9y ago

> But I’ll try to explain everything technically and stay objective You failed inside of 3 paragraphs.

moduspol 9y ago
The headline used the term "BCash." It'd be tough to have an objective post by someone about "BCore," too.

stale2002 9y ago

OK, this is describing a 51% attack. And who would engage in this 51% attack? The miners? The miners are one of the biggest groups that SUPPORT Bitcoin Cash, so I find it unlikely that they would spend millions attacking it. Anyway. It matters not. The people that want Bitcoin to be a settlement layer are free to spend 50$ per transaction to use Bitcoin, and those of us who want to use it as an actual peer to peer electronic currency will use Bitcoin Cash. Everyone wins. It doesn't really matter what is the "real" Bitcoin.

mplewis 9y ago
Anyone who's mining Bitcoin could switch to Bitcoin Cash and work to perform a 51% attack. > BCash shares hashing algorithm with Bitcoin. That means any hashing power on the Bitcoin network can work on BCash network. And there is typically 10 times more miners mining on BTC, than on BCH because of the difference in the price and minning fees.
- stale2002 9y ago
  And which miner SPECIFICALLY would do that? There are only like 7 major mining pools. Which of those 7 do you think would do an attack? The miners were the ones who helped create Bitcoin Cash. Why would they attack it? The miners are the largest supporters of big blocks, so it make no sense that they would attack the thing that they helped launch. Also, people don't seem to realize that it is already possible to do a ~20 percent selfish mining attack. And yet we don't see THAT happening... These attacks aren't realistic in practice because it would be immediately obvious that something is happening, and the miners would lose all their money as Bitcoin crashes.
  - yourrng 9y ago
    Let me count some scenarios: * a miner losing its share in the competitive game could make a one last money grab before its hardware is obsolete * BCash backing miners losing confidence in success of BCH could just damage the whole space, for revenge or and profit * complete outsider like an angry government could try to disrupt the space to ban all crypto or at least heavily regulate it / buy some time

ErikAugust 9y ago

Is it possible it's already happened? I have no idea what the mining breakdown looks like - but I'd imagine it's only a couple players mining BCH. I'd think you could rewrite the chain at will pretty much.

VMG 9y ago
We would see two chains forking of a shared block with a significant length (~10). Unless you count Bitcoin Clashic[1], there's no proof of that http://bitcoinclashic.org/ http://bitcoinclashic.org/

bishopknight 9y ago

Not happening. ANT Pool has a huge investment in Bitcoin Cash and would swoop in with mining power to protect their investment.

yourrng 9y ago
Please re-read the post, because you don't understand. The 51% attack is carried in secret. Noone has any way to know if it is happening until the longer chain is published. And after that, it's too late already. Someone could try to catch up with (not anymore secret) longest chain, but the damage has been done - the state of the network has already changed. Actually switching it back is only adding salt to the wound. Noone would trust that coin again anyway, and it is worthless to try to rescue it. AntPool is busy mining Bitcoin, because it pays better: https://blockchain.info/pools https://blockchain.info/pools so it can't constantly police BCash chain by over-provisioning it.
- deleted 9y ago
  [deleted]
VMG 9y ago
How would they protect it after a double spend occurred?

toomim 9y ago

A 51% attack only allows you to (1) censor transactions for a short time, and (2) double-spend. The first part is a mild nuisance. The second one can be retaliated against off-chain, which puts the attacker (who must be a large entity) at great risk in the real world.

VMG 9y ago
> The second one can be retaliated against off-chain. What do you mean?
- chc 9y ago
  I believe it means that the recipient of the double-spent transaction can sue you or send goons after you just like they would someone who defrauded them without using cryptocurrency.
  - VMG 9y ago
    How would you determine the culprit? You can't even prove that there was an intent to roll back a particular transaction.
    - cperciva 9y ago
      No, but you can show that there was an intention to double-spend coins.
- gizmo686 9y ago
  If you do a double spend attack of any significance, the other party will notice. Unless you are doing something completely anonymous, the other party will also know who you are and be able to pursue other remedies (eg. sue you for fraud).
  - VMG 9y ago
    If double-spend detection rather than prevention was enough, you could build a much cheaper and more efficient payment system than Bitcoin. What makes Bitcoin interesting is the fact that you don't have to resort to the legal system for final arbitration.

ubu7737 9y ago

The spectrum is really marvelous. It's amazing to see how many different kinds of people, with many different motivations, will waste their time on speculative crypto-coins.

jVinc 9y ago

I like the math and theory on this. But really why would someone who's making millions on the status quo risk tanking the market for a one time gain? Seems unlikely.

yourrng 9y ago
You don't have to risk anything. If the trend continues, at some point one would be able to rent the mining power required. On top of it, if you are a small miner, and you can't afford capital investments required to keep up with latest mining hardware, while loosing market share, you can use your soon-osolete hardware to make a one last buck. A big buck this time.
- xiphias 9y ago
  At this point 5-10% of hash rate is a huge cost in mining hardware (maybe hundreds of millions). Also the hardware improvements already slowed down a lot. Antminer S9 is more than a year old. I wouldn't risk decreasing the BTC price by attacking BCH.
soared 9y ago
Any organization/individual/government who has enough money that they aren't interested in cashing out and is also interested in medium/large scale economic disruption. China, Russia, UAE, USA, sci-fi terrorists, evil villains, illuminati etc. (I'm only mostly joking)
SAI_Peregrinus 9y ago
One possibility would be to keep up and coming competitor currencies from gaining a foothold. The big ASIC mining farms bitcoin has won't work with some of the smaller currencies. The organizations running them have a lot of money, and don't necessarily want to see competition from less centralized mining. Destroying trust in a currency by executing a double spend attack on it could be one way to prevent that.

omarforgotpwd 9y ago

Who is seriously going to try and execute a 51% attack? It would be so incredibly expensive, you would have to keep spending more as people added hash power to shut you out, and most importantly if your attack worked you would instantly undermine the security of the blockchain making all the currency you've stolen worthless!

deftnerd 9y ago

I can't take any criticisms against Bitcoin Cash seriously when the authors knowingly refer to it as BCash. It's not just a shortening of the name, it's part of a concerted effort by detractors to distance the chain from the Bitcoin legacy. Any author that purposefully uses the term BCash is, on the face, incapable of being objective because they're advertising that they're detractors already. The Bitcoin Core (no on-chain scaling at any cost!) crowd asked the on-chain scaling fans to "fork off and leave". Now that the coin is doing very well in terms of market value and especially in growing merchant adoption, they're desperate to push the narrative that it's a scam or dangerous or can't be taken seriously. They know that if they can't destroy Bitcoin Cash now, it has a reasonable chance of eventually overtaking the legacy Bitcoin network in every important respect.

MintPattern 9y ago
It’s called bcash in hopes that too many newbies won’t go deposit bitcoin into a “bitcoin cash” address and sadly lose it all.
- zepolen 9y ago
  Why would he lose it?
- toomim 9y ago
  Again, this is a myth spread by people trying to tarnish Bitcoin Cash's image. The truth is that the money can't be lost. If you have the Bitcoin Cash private keys for the deposit address, you have the Bitcoin Core private keys on the Core chain. All that happens is that someone accidentally receives Bitcoin Core instead of Cash.
  - deleted 9y ago
    [deleted]
  - MintPattern 9y ago
    A lot of newbies put everything on an online exchange and don't bother with handling private keys. I haven't found a single exchange yet where you control the private keys. The public keys on exchanges I've seen are different for Bitcoin Cash and Bitcoin. Also, can you imagine the end result of paying for a good or service that accepts Bitcoin with Bcash?

JepZ 9y ago

When the BTC-BCH split happend I didn't really understand what everybody was talking about transaction fees. So after BTC continued to rise the past months and we have transaction fees >20$ I understand what was discussed earlier this year. I just wonder why the core devs were against increasing the blocksize. Yes, it would not have been a solution for the next 20 years, but at least it would have left the fees at a place where BTC was still suitable for the everyday use until other solutions could be established.

moduspol 9y ago
I think they have valid arguments for keeping smaller blocks, but this FUD is getting ridiculous. This very post has no new ideas, has no listed author, and is posted by a two hour old user account. It's not even about discussing what's best for Bitcoin any more.
notsrg 9y ago
Increasing the blocksize increases centralization at a time where miners have unprecedented power.
- JepZ 9y ago
  How does it increase centralization and why have miners more power than 5 years ago? (Just because the value increased? Do they have more influence to the community?) Could you pleace elaborate on that?
  - exit 9y ago
    it increases centralisation because large blocks do not propagate as easily, and therefore encourage mining co-location
fizzbuzzbazz3 9y ago
There are many technical reasons, but I'll respond differently. Bitcoin is not a business-coin. Bitcoin is an idea-coin. It was never about the price, the price is just a side-effect. For many early adopters and developers, Bitcoin is about changing the world. Not in a marketing bullshit-world, but in a real way. We really believe that the world would be a better place if we've put a stop to government and banks monopoly on controlling the money. You may disagree, and it's fine. We believe in it, and we want to have the most secure, uncensorable and attack-resistant value transferring network. If it takes $30 to pay to transfer on such network, so be it. Increasing the block size compromises on that property, so we are not willing to do it, even though it's painful for everyone. We will wait. We have credit cards, we PayPal, and we can use altcoins before we get there. The price will rise and fall, users will come and go. We held at $1, we held at $10, we held at $20k, and we will hold at $10 again if it's required. We will get our layer 2 solution and get both our uncensorable, government-resistant network and instant cheap micropayments. That's why most of us dumped BCH coins without thinking twice. What most other coins are (not all!) is a business-coin. They are mostly pointless. Ethereum could be really a centralized smart-contracts platform run by Google or Amazon, and noone would care much. Actually, I believe that's how ETH is going to end. I believe Amazon engineers are working on it already. Because who cares about centralization or censorship resistance, if the main use case is breading virtual cats? No government will be interested in censoring that. What BCash is, is a scam coin. It's all about ASICBOOST and Roger Ver's hurt pride. He would like to be a pope of Bitcoin, but noone really cares about him. Except for a talent for scamming people for his own gain, he is noone.