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Tue, 2 Mar 2021 10:22:06 -0800 (PST) To: bitcoin-dev@lists.linuxfoundation.org References: <202102281933.30691.luke@dashjr.org> From: Chris Belcher Autocrypt: addr=belcher@riseup.net; prefer-encrypt=mutual; keydata= xsFNBFPk74oBEACzBLjd+Z5z7eimqPuObFTaJCTXP7fgZjgVwt+q94VQ2wM0ctk/Ft9w2A92 f14T7PiHaVDjHxrcW+6sw2VI2f60T8Tjf+b4701hIybluWL8DntG9BW19bZLmjAj7zkgektl YNDUrlYcQq2OEHm/MGk6Ajt2RA56aRKqoz22e+4ZA89gDgamxUAadul7AETSsgqOEUDI0FKR FODzoH65w1ien/DLkG1f76jd0XA6AxrESJVO0JzvkTnJGElBcA37rYaMmDi4DhG2MY4u63VE 8h6DyUXcRhmTZIAj+r+Ht+KMDiuiyQcKywCzzF/7Ui7YxqeAgjm5aPDU2E8X9Qd7cqHQzFM7 ZCqc9P6ENAk5a0JjHw0d0knApboSvkIJUB0j1xDIS0HaRlfHM4TPdOoDgnaXb7BvDfE+0zSz WkvAns9oJV6uWdnz5kllVCjgB/FXO4plyFCHhXikXjm1XuQyL8xV88OqgDFXwVhKrDL9Pknu sTchYm3BS2b5Xq1HQqToT3I2gRGTtDzZVZV0izCefJaDp1mf49k2cokDEfw9MroEj4A0Wfht 0J64pzlBYn/9zor5cZp/EAblLRDK6HKhSZArIiDR1RC7a6s7oTzmfn0suhKDdTzkbTAnDsPi Dokl58xoxz+JdYKjzVh98lpcvMPlbZ+LwIsgbdH4KZj7mVOsJwARAQABzR9DaHJpcyBCZWxj aGVyIDxmYWxzZUBlbWFpbC5jb20+wsF+BBMBAgAoBQJT5O+KAhsDBQkSzAMABgsJCAcDAgYV CAIJCgsEFgIDAQIeAQIXgAAKCRDvc06md/MRKS8jD/9P9fSYSIVjltL9brAMfIu7wJn0H0lX TbcuCM2uQitJ3BNxI3c7aq5dEby27u5Ud54otncDJuRPQVDKs6H7t1rInitgJ1MTQ9/aQGFA btKcgtVIMFbeClzTTfWr4W7fE45NI7E9EANgk5JfmWh3U+KINYLF5RtqynYocrsP6zOV+G9A HCpBemd9TN60CoMLMyMzTHEW1oQffaVAXY8DgthEYO/odWYIod7VTmEm0zU1aSysPqMwPWNm 8XIl0f8SfKQyZlAU8e1eCFVCenkE44FKC5qQNYc2UxexEYtfCWChTGc4oHKxIyYmTCCefsQF LvgwtvlNHRXHSDKSPSNcRcpl8DFpNEKrmMlkJ8Mx+YR05CydlTQ0bI3FBohJC+UHrjD5I3hA wJUC1o+yVSOEd+zN3cG1EECIwkEQSmBgG5t/le2RdzfXOdpf9ku2/zoBpq00R54JxUKlfRM7 OPTv7X+1AKHkxOySdCZwGgvdh2Whuqs4kTvtco00gCFM9fBd5oi1RJuHtxHsj8+/XU15UItb jeo96CIlM5YUeoRLPT5mxZYWgYAARFeSFReNq/Tuwq9d8EokUrtAyrPayznliy53UJfWDVzl 925c0Cz0HWaP2fWj+uFcj/8K0bhptuWJQy0Poht1z3aJC1UjEgr1Xz8I7jeSJmIlA9plcJw2 k4dhWc7BTQRT5O+KARAAyFxAM28EQwLctr0CrQhYWZfMKzAhCw+EyrUJ+/e4uiAQ4OyXifRr ZV6kLRul3WbTB1kpA6wgCShO0N3vw8fFG2Cs6QphVagEH8yfQUroaVxgADYOTLHMOb7INS8r KI/uRNmE6bXTX27oaqCEXLMycqYlufad7hr42S/T8zNh5m2vl6T/1Poj2/ormViKwAxM+8qf xd8FNI4UKmq2zZE9mZ5PiSIX0qRgM0yCvxV39ex/nhxzouTBvv4Lb1ntplR/bMLrHxsCzhyM KDgcX7ApGm+y6YEsOvzw9rRCRuJpE4lth8ShgjTtNTHfklBD6Ztymc7q7bdPWpKOEvO5lDQ6 q8+KfENv862cOLlWLk7YR2+mHZ1PXGhWC7ggwEkfGJoXo0x8X+zgUKe2+9Jj4yEhfL0IbFYC z2J5d+cWVIBktI3xqkwLUZWuAbE3vgYA4h8ztR6l18NTPkiAvpNQEaL4ZRnAx22WdsQ8GlEW dyKZBWbLUdNcMmPfGi5FCw2nNvCyN6ktv5mTZE12EqgvpzYcuUGQPIMV9KTlSPum3NLDq8QI 6grbG8iNNpEBxmCQOKz2/BuYApU2hwt2E44fL8e6CRK3ridcRdqpueg75my6KkOqm8nSiMEc /pVIHwdJ9/quiuRaeC/tZWlYPIwDWgb8ZE/g66z35WAguMQ+EwfvgAUAEQEAAcLBZQQYAQIA DwUCU+TvigIbDAUJEswDAAAKCRDvc06md/MRKaZwD/9OI3o3gVmst/mGx6hVQry++ht8dFWN IiASPBvD3E5EWbqWi6mmqSIOS6CxjU0PncxTBPCXtzxo/WzuHGQg/xtNeQ0T8b2lBScZAw93 qm1IcHXLUe5w/Tap6YaDmSYCIZAdtbHzYfPW4JK7cmvcjvF8jhTFOBEOFVQkTi19G7caVot0 +wL1e2DRHDXAe5CinEpaLBlwHeEu/5j6wc3erohUZlK9IbAclj4iZTQbaq3EyqUXl59dBOON xmL5edJxzVishIYQGIyA9WP1SylXt+kO82NEqZG2OxdXAlzjuJ8C2pAG+nbLtDo4hcsiN/MA aX9/JB7MXclT5ioerF4yNgKEdfq7LmynsTUd8w/Ilyp7AD+BWoujyO94i8h9eKvjf9PvSwxQ uAjRpxne7ZJD8vCsMNXBHSbeEK2LiwStHL/w473viXpDD53J6OLxX6a5RummR+rixbMH7dgK MJQ7FlyDphm3or6CSkGEir1KA0y1vqQNFtHhguFapAWMDKaJjQQNgvZUmOo6hbZqmvUF1OWc d6GA6j3WOUe3fDJXfbq6P9Jmxq64op887dYKsg7xjQq/7KM7wyRcqXXcbBdgvNtVDP+EnzBN HyYY/3ms4YIHE5JHxQ9LV4yPcWkYTvb1XpNIFVbrSXAeyGHVNT+SO6olFovbWIC3Az9yesaM 1aSoTg== Message-ID: Date: Tue, 2 Mar 2021 18:21:59 +0000 MIME-Version: 1.0 In-Reply-To: <202102281933.30691.luke@dashjr.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [bitcoin-dev] LOT=False is dangerous and shouldn't be used X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 02 Mar 2021 18:22:15 -0000 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 > bitcoin-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev >