Hearn's Worst Case Scenario: Checkpoints in XT to "ignore the longest chain"

[Westin Landon Cox]

There was part of the discussion with Mike Hearn on Epicenter Bitcoin last week that I haven't seen discussed. I cut out the relevant 2 or 3 minutes:

https://youtu.be/DB9goUDBAR0

Here is part of what he said:

Do we really have the majority we think we do? ... There's nothing like measuring it for real. The worst case scenario is the majority ... the economic majority ... is in favor but the hash power, the mining majority is not. That would be a very messy situation for bitcoin.

There've been concerns raised by mining pools in China where a lot of mining has been going on that their connectivity has been extremely poor compared to the rest of the internet for a bunch of reasons. If the needs of the wider global bitcoin community start diverging from what miners in China want, then who wins? The answer is the economic majority wins, right, the wider community wins, but it would require a bit of a technical mess to sort everything out in that case.

... If we imagine this kind of worst case scenario happening, they would ignore the longest chain. Doesn't matter that it's the longest if it's ... um ... uh ... you know ... well, let me rephrase that.

... If miners were building a longer chain than the 20 Meg chain, then the client would keep switching back to it and keep ending up with this bigger and bigger backlog. At that point what we would have to do is like checkpoint blocks into both the full nodes and the SPV wallets. So that's a much larger and more complicated upgrade to force it onto the "larger" chain, right.

In the worst case scenario if the miners and the rest of the bitcoin community end up in some kind of full-fledged war, that would basically wreck bitcoin.

I keep reading that the fork wouldn't take place until "90%" of nodes and/or miners have upgraded, but that doesn't sound like what Hearn is describing at all.

I'm not against lifting the hard block size limit from 1MB to 20MB (or some compromise like 8MB), but trying to do it without the miners in China sounds like a disaster. I'm strongly against putting checkpoints into the code to "ignore the longest chain." It's scary to think the idea even sounds reasonable.

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[tvbcof]

Jeez I'm glad to see at least one person paying some attention.

I would have thought that at this point Hearn's best strategy would be to bluster over this issue.  Perhaps he felt constrained by some of the interviews with the miners.

The idea of how to subvert the 'longest chain' is not new.  It would be needed in some cases to overcome a 51% attack, and more recently in the context of a fork war which is basically the same principle.  A guy who wins control of the MultiBitch client fleet has a leg-up on his competition, and I've for years felt that this was the driving force behind developing such a fleet.

In my own musings about the problem, I assumed that the chain I favored would not be the longest.  Mike's admission that he may have the same problem is very heartening since it means that my favored chain might actually not have it!

One of the most interesting take-aways is that Mike anticipates the need for continuous checkpoints.  What I read into this is that he (like myself) is not anticipating a single chain as the competition but a stream of them.  (The world will look morphologicaly more like a hydra than it does a slingshot.)  If it were a simple 'Y' shape then a single blacklisting of a block in the 'wrong' chain would be sufficient to identify it.

[Westin Landon Cox]

One of the most interesting take-aways is that Mike anticipates the need for continuous checkpoints.  What I read into this is that he (like myself) is not anticipating a single chain as the competition but a stream of them.  (The world will look morphologicaly more like a hydra than it does a slingshot.)  If it were a simple 'Y' shape then a single blacklisting of a block in the 'wrong' chain would be sufficient to identify it.

Wow. I was just thinking about a simple 'Y' fork. What you're describing ... well, at least it would be interesting to watch.

The more I think about what Mike Hearn is saying in this clip, the more I'm inclined to switch sides. I was basically passively OK with 20MB, but I'm definitely not OK with a Bitcoin with centralized checkpoints. I'll be surprised if a majority of the Bitcoin community is OK with that.

[nicked]

This is really disturbing. I might just forget about bitcoin for awhile.

[Carlton Banks]

The more I think about what Mike Hearn is saying in this clip, the more I'm inclined to switch sides. I was basically passively OK with 20MB, but I'm definitely not OK with a Bitcoin with centralized checkpoints. I'll be surprised if a majority of the Bitcoin community is OK with that.

Yep, increase the block size is an obvious yes. Hostile fork to achieve it? Nope. Especially not if any possibility for tragic outcomes for both forks exists at all.

(it also possibly needs some mechanism to smooth the transition to bigger blocks, and/or a target size with incentives to stay on target etc)

[LiteCoinGuy]

but he is not the only person who will read and test the code. lets see what other devs say about that.

[unamis76]

This doesn't really sound good indeed... But fortunately it's the worst case scenario, and an improbable one.No miner will want things to get ruined

[tvbcof]

This doesn't really sound good indeed... But fortunately it's the worst case scenario, and an improbable one.No miner will want things to get ruined

Be careful about this.  Anyone sitting on multiple millions of dollars worth of hardware is under threat.  Miners will make the best choices for themselves in any particular scenario and that may or may not correspond to the long-term health of Bitcoin proper.

Bitcoin as a blockchain with embedded value is probably around for the duration baring some fundamental and unknown (to me) weakness in certain of the cryptography.  Bitcoin as a viable method of wealth protection and transfer is subject to periods of hiatus.  I'd actually be quite surprised to see it be healthy and accessible in a time of economic crisis impacting the USD.  As a corollary, I'd be surprised if all of the factors used to simulate Bitcoin's natural collapse (absent a bloatfork) were equally communicated.

[Westin Landon Cox]

but he is not the only person who will read and test the code. lets see what other devs say about that.

I think Hearn is the only person who decides what code is included in XT. I don't even think Gavin Andresen has commit access to XT.

[unamis76]

This doesn't really sound good indeed... But fortunately it's the worst case scenario, and an improbable one.No miner will want things to get ruined

Be careful about this.  Anyone sitting on multiple millions of dollars worth of hardware is under threat.  Miners will make the best choices for themselves in any particular scenario and that may or may not correspond to the long-term health of Bitcoin proper.

Bitcoin as a blockchain with embedded value is probably around for the duration baring some fundamental and unknown (to me) weakness in certain of the cryptography.  Bitcoin as a viable method of wealth protection and transfer is subject to periods of hiatus.  I'd actually be quite surprised to see it be healthy and accessible in a time of economic crisis impacting the USD.  As a corollary, I'd be surprised if all of the factors used to simulate Bitcoin's natural collapse (absent a bloatfork) were equally communicated.

They are obviously under threat, that's why it's in their best interest to keep Bitcoin running smoothly and do everything for it's success... If Bitcoin is in good standing, so the miners are, I think. I'm not really seeing a situation where, for example, miners win and merchants loose. If merchants loose, miners will too in the long term, because Bitcoin will suffer... And it will suffer in price, and miners won't enjoy that, obviously

But I may be wrong. What kind of best choice for miners are you thinking in that doesn't correspond to the long term health of Bitcoin?

[MicroGuy]

Hearn has a solution for all the Chinese miners stuck on the old chain, they can develop their own Chinese-specific altcoin. 

If that's really the case, it seems to me that Chinese Bitcoin is unsustainable and what you really need is a China-specific alt coin that can run entirely within the Chinese internet.

http://sourceforge.net/p/bitcoin/mailman/message/34162353/

[NUFCrichard]

The more I think about what Mike Hearn is saying in this clip, the more I'm inclined to switch sides. I was basically passively OK with 20MB, but I'm definitely not OK with a Bitcoin with centralized checkpoints. I'll be surprised if a majority of the Bitcoin community is OK with that.

Yep, increase the block size is an obvious yes. Hostile fork to achieve it? Nope. Especially not if any possibility for tragic outcomes for both forks exists at all.

(it also possibly needs some mechanism to smooth the transition to bigger blocks, and/or a target size with incentives to stay on target etc)

A hostile chain will never work.  The main exchange established for carries the value, someone would need to persuade them to adopt the hostile chain to have any real effect.

Miners mine to make money, so they will do what the exchanges do.

[ArticMine]

I am and have been a very strong supporter of increasing the blocksize limit and making the blocksize limit to increase with time to allow for the growth of Bitcoin; however a hostile chain is not the way to go about this. One can argue for a lower threshold to tigger the fork, say 70% of the hashpower; however this means that the longest chain is still supporting the fork.

[Jimmy Crypto]

Wow. Bitcoin XT is now an altcoin? 

[shorena]

Hearn has a solution for all the Chinese miners stuck on the old chain, they can develop their own Chinese-specific altcoin. 

If that's really the case, it seems to me that Chinese Bitcoin is unsustainable and what you really need is a China-specific alt coin that can run entirely within the Chinese internet.

http://sourceforge.net/p/bitcoin/mailman/message/34162353/

Sounds like a bad idea to just cast a big part of the community out, because... uhm well, their internet sucks. Id rather see O(1) block propagation with the increased block size among some other changes. I dont think this problem can be solved by just changing one screw and hope for the best. We need bigger blocks in order for bitcoin to keep growing. We need O(1) propagation to keep miners on board with the bigger blocks. We need elastic blocksize limits to discourage spam blocks as well as a good algorithm to determine blocksize growth. Both is needed to keep a fee market. The substitution will end some day, lets not forget that. We also need pruning to keep non mining nodes cheap. There are possibly other things Im missing, but this is a big step and most current solutions I see are basically kicking the can down the road or forget/ignore part of the network.

[SebastianJu]

Wow. Bitcoin XT is now an altcoin? 

Thats what i wonder too. Why is this thread in Altcoin Discussion. I think it should be moved to Bitcoin Discussion. It doesnt have to do anything with altcoins.

Im not a fan of Bitcoin XT, its not why i write this, the simply risks of "our" coin becoming the coin of a company is not for me. Though i think this discussion should be discussed in the correct place.

[Westin Landon Cox]

Wow. Bitcoin XT is now an altcoin? 

Thats what i wonder too. Why is this thread in Altcoin Discussion. I think it should be moved to Bitcoin Discussion. It doesnt have to do anything with altcoins.

Im not a fan of Bitcoin XT, its not why i write this, the simply risks of "our" coin becoming the coin of a company is not for me. Though i think this discussion should be discussed in the correct place.

I originally posted it in Bitcoin Discussion. I guess a mod moved it to Altcoin Discussion. I don't mind though. I laughed when I saw it'd been moved here.

[Scott J]

I see Theymos has the same XT policy here as he does on r/bitcoin 

[Mickeyb]

Man, this is getting more and more ridiculous! Freaking checkpoints now! I am just waiting to see what will I read next tomorrow when I wake up!

[MarketNeutral]

Your papers, please!