To clarify, it is the soft fork enforcement by majority hash power that is the 51% attack, not the stopping of it. Majority hash power censors non-conforming transactions. To counter it requires only a non-censoring majority to continue mining.
It is correct that the purpose of supermajority signaling is to reduce the chance of a chain split. It is misleading to call it a bug and to imply that user activation isn’t actually intended to create, or at least threaten, a chain split. It’s a game of chicken. e > On Mar 2, 2021, at 10:22, Chris Belcher via bitcoin-dev > <[email protected]> wrote: > > It is wrong to say that using miner signalling alone for activation > (LOT=false) is a bug. > > As we vividly saw in the events of the 2017 UASF, the purpose of miner > signalling isn't to activate or enforce the new rules but to stop a > chain split. A majority of miners can stop a chain split by essentially > doing a 51% attack. Such attacks have been known about since day one, > and even the whitepaper writes about them. > > So they are not a bug but an inherent part of the way bitcoin works. If > fixing this issue was a simple as setting a consensus rule parameter > then bitcoin would have been invented decades earlier than it was. > > And certainly miner signalling cannot be compared to an inflation bug. > The inflation rules are enforced by the economy using full nodes, but > chain splits or lack of them is enforced by miners. They are two > different parts of the bitcoin system. Back in 2010 there was an > inflation bug CVE-2010-5139 (the "Value overflow incident") which proves > my point. Even though miners created a block which printed 184 billion > bitcoins, the economy quickly adopted a patch which fixed the bug and > miners switched over to the correct chain which soon overtook the bugged > chain (there was a reorg of 53 blocks). > > > > > Also another point: in a hypothetical chain split it's true that the > LOT=false chain would be vulnerable to reorgs, but it's also true that > the LOT=true would suffer from slow blocks. > > So for example, imagine trading bitcoin for cash in person, but instead > of waiting on average 10 minutes for a confirmation you have to wait 2 > hours. Imagine depositing coins to an exchange which requires 3 > confirmation, then instead of waiting ~30 minutes you have to actually > wait 6 hours. This is a significant degradation in usability. The > situation is a mirror image of how the LOT=false chain is vulnerable to > reorgs. Both chains suffer if a chain split happens which is why they > are pretty important to avoid. That's why its inaccurate to portray > LOT=true chain as safe with no downsides at all. > > > > >> On 28/02/2021 19:33, Luke Dashjr via bitcoin-dev wrote: >> (Note: I am writing this as a general case against LOT=False, but using >> Taproot simply as an example softfork. Note that this is addressing >> activation under the assumption that the softfork is ethical and has >> sufficient community support. If those criteria have not been met, no >> activation should be deployed at all, of any type.) >> >> As we saw in 2017 with BIP 9, coordinating activation by miner signal alone, >> despite its potential benefits, also leaves open the door to a miner veto. >> This was never the intended behaviour, and a bug, which took a rushed >> deployment of BIP148 to address. LOT=False would reintroduce that same bug. >> It wouldn't be much different than adding back the inflation bug >> (CVE-2018-17144) and trusting miners not to exploit it. >> >> Some have tried to spin LOT=True as some kind of punishment for miners or >> reactive "counter-attack". Rather, it is simply a fallback to avoid >> regression on this and other bugs. "Flag day" activation is not >> fundamentally >> flawed or dangerous, just slow since everyone needs time to upgrade. >> BIP 8(LOT=True) combines the certainty of such a flag day, with the speed >> improvement of a MASF, so that softforks can be activated both reasonably >> quick and safely. >> >> In the normal path, and that which BIP8(True) best incentivises, miners will >> simply upgrade and signal, and activation can occur as soon as the economic >> majority is expected to have had time to upgrade. In the worst-case path, >> the >> behaviour of LOT=True is the least-harmful result: unambiguous activation >> and >> enforcement by the economy, with miners either deciding to make an >> anti-Taproot(eg) altcoin, or continue mining Bitcoin. Even if ALL the miners >> revolt against the softfork, the LOT=True nodes are simply faced with a >> choice to hardfork (replacing the miners with a PoW change) or concede - >> they >> do not risk vulnerability or loss. >> >> With LOT=False in the picture, however, things can get messy: some users >> will >> enforce Taproot(eg) (those running LOT=True), while others will not (those >> with LOT=False). Users with LOT=True will still get all the safety thereof, >> but those with LOT=False will (in the event of miners deciding to produce a >> chain split) face an unreliable chain, being replaced by the LOT=True chain >> every time it overtakes the LOT=False chain in work. For 2 weeks, users with >> LOT=False would not have a usable network. The only way to resolve this >> would >> be to upgrade to LOT=True or to produce a softfork that makes an activated >> chain invalid (thereby taking the anti-Taproot path). Even if nobody ran >> LOT=True (very unlikely), LOT=False would still fail because users would be >> faced with either accepting the loss of Taproot(eg), or re-deploying from >> scratch with LOT=True. It accomplishes nothing compared to just deploying >> LOT=True from the beginning. Furthermore, this process creates a lot of >> confusion for users ("Yep, I upgraded for Taproot(eg). Wait, you mean I have >> to do it AGAIN?"), and in some scenarios additional code may be needed to >> handle the subsequent upgrade cleanly. >> >> To make matters worse for LOT=False, giving miners a veto also creates an >> incentive to second-guess the decision to activate and/or hold the >> activation >> hostage. This is a direct result of the bug giving them a power they weren't >> intended to have. Even if we trust miners to act ethically, that does not >> justify sustaining the bug creating both a possibility and incentive to >> behave unethically. >> >> So in all possible scenarios, LOT=False puts users and the network at >> significant risk. In all possible scenarios, LOT=True minimises risk to >> everyone and has no risk to users running LOT=True. >> >> The overall risk is maximally reduced by LOT=True being the only deployed >> parameter, and any introduction of LOT=False only increases risk probability >> and severity. >> >> For all these reasons, I regret adding LOT as an option to BIP 8, and think >> it >> would be best to remove it entirely, with all deployments in the future >> behaving as LOT=True. I do also recognise that there is not yet consensus on >> this, and for that reason I have not taken action (nor intend to) to remove >> LOT from BIP 8. However, the fact remains that LOT=False should not be used, >> and it is best if every softfork is deployed with LOT=True. >> >> Luke >> _______________________________________________ >> bitcoin-dev mailing list >> [email protected] >> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev >> > _______________________________________________ > bitcoin-dev mailing list > [email protected] > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev _______________________________________________ bitcoin-dev mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
