So why all the hate on segwit?
The short answer: Ill-informed nincompoops who overestimate their own competence enjoy voicing opinions to which they are not entitled; and all which cannot be explained by stupidity, is caused by malice. Cui bono? “Follow the money.”
Longer answer, for those who wish to actually understand this issue:
The following told me all I needed to know about the anti-Segwit agitation and later, the so-called “Bitcoin Cash” scamcoin. For more technical details, see also the references listed in the Common Vulnerabilities and Exposures database under CVE-2017-9230, or the high-level description by Test User earlier in this thread. N.b. that without Segwit, covert ASICBOOST is still wide-open for exploitation in “Bitcoin Cash”.
With boldface added, from this bitcoin-dev mailing list post on 2017-04-05 21:37:45 UTC:
Quote from: Gregory Maxwell
A month ago I was explaining the attack on Bitcoin's SHA2 hashcash which is exploited by ASICBOOST and the various steps which could be used to block it in the network if it became a problem.
While most discussion of ASICBOOST has focused on the overt method of implementing it, there also exists a covert method for using it.
As I explained one of the approaches to inhibit covert ASICBOOST I realized that my words were pretty much also describing the SegWit commitment structure.
The authors of the SegWit proposal made a specific effort to not be incompatible with any mining system and, in particular, changed the design at one point to accommodate mining chips with forced payout addresses.
Had there been awareness of exploitation of this attack an effort would have been made to avoid incompatibility-- simply to separate concerns. But the best methods of implementing the covert attack are significantly incompatible with virtually any method of extending Bitcoin's transaction capabilities; with the notable exception of extension blocks (which have their own problems).
An incompatibility would go a long way to explain some of the more inexplicable behavior from some parties in the mining ecosystem so I began looking for supporting evidence.
Reverse engineering of a particular mining chip has demonstrated conclusively that ASICBOOST has been implemented in hardware.
[…]
Due to a design oversight the Bitcoin proof of work function has a potential attack which can allow an attacking miner to save up-to 30% of their energy costs (though closer to 20% is more likely due to implementation overheads).
Timo Hanke and Sergio Demian Lerner claim to hold a patent on this attack, which they have so far not licensed for free and open use by the public. They have been marketing their patent licenses under the trade-name ASICBOOST. The document takes no position on the validity or enforceability of the patent.
While most discussion of ASICBOOST has focused on the overt method of implementing it, there also exists a covert method for using it.
As I explained one of the approaches to inhibit covert ASICBOOST I realized that my words were pretty much also describing the SegWit commitment structure.
The authors of the SegWit proposal made a specific effort to not be incompatible with any mining system and, in particular, changed the design at one point to accommodate mining chips with forced payout addresses.
Had there been awareness of exploitation of this attack an effort would have been made to avoid incompatibility-- simply to separate concerns. But the best methods of implementing the covert attack are significantly incompatible with virtually any method of extending Bitcoin's transaction capabilities; with the notable exception of extension blocks (which have their own problems).
An incompatibility would go a long way to explain some of the more inexplicable behavior from some parties in the mining ecosystem so I began looking for supporting evidence.
Reverse engineering of a particular mining chip has demonstrated conclusively that ASICBOOST has been implemented in hardware.
[…]
Due to a design oversight the Bitcoin proof of work function has a potential attack which can allow an attacking miner to save up-to 30% of their energy costs (though closer to 20% is more likely due to implementation overheads).
Timo Hanke and Sergio Demian Lerner claim to hold a patent on this attack, which they have so far not licensed for free and open use by the public. They have been marketing their patent licenses under the trade-name ASICBOOST. The document takes no position on the validity or enforceability of the patent.
Observe that a purported patent on a 20+% economic advantage threatens to give certain parties a substantial centralized influence over who has the most hashrate. It is not only cheating: Overall, covert ASICBOOST opens the way for a direct attack against the Byzantine fault-tolerant security of the Bitcoin network.
So as for ulterior motives to oppose Segwit. What overt arguments are advanced by the anti-Segwit side?
On the presumption that Segwit-haters must have at least some plausible excuse for their position, I have spent far too many hours searching the Net and reading what they say. My objective: Find even one good reason to oppose Segwit on technical grounds. Yet despite my such efforts, I have never seen a valid technical argument against Segwit. All the anti-Segwit pseudo-technical arguments are unsubstantive handwaving—yes, it’s a moderately big patch; of course, it’s a big feature!—or bald-faced lies—e.g., the claim that miners could collude to grab “anyone-can-spend” transactions; no, Segwit full nodes would reject such such blocks as invalid, making such miners waste all their effort.[1] (This last is not even a Segwit-specific matter: Any soft fork will result in similar scenarios, which is exactly what makes the fork “soft” even when introducing radically different validation rules. The alternative is a hardfork.)
The rest of the anti-Segwit arguments are nontechnical. Some make menacing insinuations about Blockstream: Very well, assume arguendo that Blockstream is pure evil (facts not in evidence) and totally controls Core (which they evidently don’t). What is so bad about Segwit? The question remains unanswered. The remainder of anti-Segwit spew is merely moronic: Insults devoid of all substance, at the puerile grade of “Segwit makes you a doodie-head”.
Meanwhile, in so-called “Bitcoin Cash”, almost three and a half months of EDA fluctuations made something tantamount to a premine of fake-Bitcoin. In that time as well as afterwards, any party exploiting covert ASICBOOST could and can reap BCH at 20+% under the energy cost paid by other miners. Oh. Suddenly, it all makes sense. Cui bono, indeed. Follow the money.
1. Miners have exactly one function: Byzantine fault-tolerant ordering of transactions. Important and valuable though that function may be, it is strictly limited in technical scope. Miners do not have authority over validation: All full nodes are responsible for enforcing validation, and will reject invalid mined blocks just as if rejecting random garbage. Such is the power of each and every individual full node. This is a point of common misunderstanding amongst ignorant fools who imagine that miners somehow own the network; and the misunderstanding is encouraged by persons with material ulterior motives for pretending that miners be Bitcoin gods.
