4 ms·

I keep hearing about an inherent problem in this capability to "resist contentious changes". In dark corners it keeps whispered that if any one entity gets cont

I keep hearing about an inherent problem in this capability to "resist contentious changes". In dark corners it keeps whispered that if any one entity gets control over 50% of the mining capacity, they can essentially decide the "immutable truth" in the blockchain. Is there any merit to that scenario, or is it complete bogus? And if it's true, how come it's not more openly discussed? I guess what I'm asking is if things like the hard fork of The DAO Ethereum blockchain are actually a fundamentally solved problem. Stuff like that happening when our banking infrastructure has moved to a blockchain sounds like a disaster.

doomrobo 9y ago
You listed two forms of control: social and computational. The latter is baked into Bitcoin and we rely on the assumption that no single entity will control >50% of the computing power of the network. This situation being "bad" is purely a consequence of the construction of the blockchain. On the other hand, the DAO fork was a result of centralized control due to social factors. As with bitcoin, a >50% consensus is necessary to fork a blockchain. But because there is a single overwhelmingly popular ethereum client, the developers had the ability to make the software obey the fork by default. A referendum was conducted in good faith, and the devs flipped the switch. But again, this was only possible because everyone was using the same client to begin with, and few people bother to change the default behavior.
- jerguismi 9y ago
  The current segwit non-adoption by miners in Bitcoin shows that with Bitcoin there clearly isn't as much social control as in ethereum. This can be bad or good, depending on viewpoint. I myself doubt that segwit will ever get adopted in bitcoin. It looks like even if a small group of actors want to block some change, they can. So that will mean that the protocol will remain pretty much the same with the good and the bad features.
- shandor 9y ago
  > the DAO fork was a result of centralized control due to social factors. As with bitcoin, a >50% consensus is necessary to fork a blockchain I'm not very well-versed in computational power requirements on this scale, but it doesn't sound at all infeasible that a nation state (or a couple in unison) could setup a "51% attack", thus reducing the social form of control back to only the computational one. And if anything, that threat is only going to become worse with ever-increasing computational capability, advent of quantum computers at some point, etc. Nations (and other huge players) have the resources to tap into all that new power, while the individuals ideally making up the bulk of a blockchain's computing power would most probably not, at least not in big enough scale. I don't see how that could be prevented, and that leaves me somewhat confused on why the blockchain is advertised as "immutable" as it is.
Taek 9y ago
It depends on the blockchain. If you run your own full node in Bitcoin, it doesn't matter what the majority hashrate is doing. If they aren't creating blocks that follow your specific rules, you can ignore them. A 51% attack cannot change the block size, for example. The ethereum ecosystem has placed a lot of trust in the ethereum foundation, plus the foundation controls a large percentage of the fully validating nodes, and is in close contact with all major miners, exchanges, etc. For this reason they are much more able to push through contentious changes. This is provably not the case in Bitcoin, as demonstrated by the active segwit vs. hardfork political deadlock.
hdhzy 9y ago
> In dark corners it keeps whispered that if any one entity gets control over 50% of the mining capacity, they can essentially decide the "immutable truth" in the blockchain. Having >50% hashing capacity allows you to arbitrarily select which transactions will or won't be confirmed. Additionally you can perform double-spends, that is the most important thing (in my opinion) that proof of work was supposed to prevent. Of course with more confirmations this attack becomes more and more expensive to execute. For details see Majority Attack [0] page on Bitcoin wiki. [0]: https://en.bitcoin.it/wiki/Majority_attack https://en.bitcoin.it/wiki/Majority_attack

doomrobo 9y ago

You listed two forms of control: social and computational. The latter is baked into Bitcoin and we rely on the assumption that no single entity will control >50% of the computing power of the network. This situation being "bad" is purely a consequence of the construction of the blockchain. On the other hand, the DAO fork was a result of centralized control due to social factors. As with bitcoin, a >50% consensus is necessary to fork a blockchain. But because there is a single overwhelmingly popular ethereum client, the developers had the ability to make the software obey the fork by default. A referendum was conducted in good faith, and the devs flipped the switch. But again, this was only possible because everyone was using the same client to begin with, and few people bother to change the default behavior.

jerguismi 9y ago
The current segwit non-adoption by miners in Bitcoin shows that with Bitcoin there clearly isn't as much social control as in ethereum. This can be bad or good, depending on viewpoint. I myself doubt that segwit will ever get adopted in bitcoin. It looks like even if a small group of actors want to block some change, they can. So that will mean that the protocol will remain pretty much the same with the good and the bad features.
shandor 9y ago
> the DAO fork was a result of centralized control due to social factors. As with bitcoin, a >50% consensus is necessary to fork a blockchain I'm not very well-versed in computational power requirements on this scale, but it doesn't sound at all infeasible that a nation state (or a couple in unison) could setup a "51% attack", thus reducing the social form of control back to only the computational one. And if anything, that threat is only going to become worse with ever-increasing computational capability, advent of quantum computers at some point, etc. Nations (and other huge players) have the resources to tap into all that new power, while the individuals ideally making up the bulk of a blockchain's computing power would most probably not, at least not in big enough scale. I don't see how that could be prevented, and that leaves me somewhat confused on why the blockchain is advertised as "immutable" as it is.

Taek 9y ago

It depends on the blockchain. If you run your own full node in Bitcoin, it doesn't matter what the majority hashrate is doing. If they aren't creating blocks that follow your specific rules, you can ignore them. A 51% attack cannot change the block size, for example. The ethereum ecosystem has placed a lot of trust in the ethereum foundation, plus the foundation controls a large percentage of the fully validating nodes, and is in close contact with all major miners, exchanges, etc. For this reason they are much more able to push through contentious changes. This is provably not the case in Bitcoin, as demonstrated by the active segwit vs. hardfork political deadlock.

hdhzy 9y ago

> In dark corners it keeps whispered that if any one entity gets control over 50% of the mining capacity, they can essentially decide the "immutable truth" in the blockchain. Having >50% hashing capacity allows you to arbitrarily select which transactions will or won't be confirmed. Additionally you can perform double-spends, that is the most important thing (in my opinion) that proof of work was supposed to prevent. Of course with more confirmations this attack becomes more and more expensive to execute. For details see Majority Attack [0] page on Bitcoin wiki. [0]: https://en.bitcoin.it/wiki/Majority_attack https://en.bitcoin.it/wiki/Majority_attack