NETWORK FREEZE bitcoin difficulty stuck high with a large hashrate drop

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stslimited:

If a large portion of the network went offline right after a difficulty increase, this scenario could freeze the bitcoin network for thousands of blocks. Basically blocks would be found MUCH more slowly to the point of it being nearly unusable.

This exact scenario happened with terracoins a few month ago. Basically what happened was that someone pointed an ASIC at terracoins and this push the difficulty EXTREMELY high, and then they stopped mining, leaving the difficulty extremely high for 8 days and no terracoin transactions were able to be processed because it took an extremely long time for the remaining miners to process any blocks.


If two of the largest miners of bitcoin went offline, the entire bitcoin economy would be at a standstill for at least several days. Although with today's makeup, just a pool could go offline and all the pool members would continue mining at a different pool. But in a different scenario, ASICMiner could have a larger portion of the network and lose connectivity right after a difficulty increase, or 6 months in the future, a different company would have 100s of terahashes more and the same thing could happen.

This is less likely with bitcoin today, but it is a real vulnerability.

In terracoin's situation the remaining hashrate was only 1/10th of what it was after the ASIC bumped the difficulty up. This isn't currently a possible scenario with bitcoin. But one could imagine a party with some future 14nm sha-256 chips developed solely to prop up the difficulty and then leave the network, making it take months until the next difficulty adjustment, making blocks take hours or days to solve, rendering transactions useless.

What can we do about that? Terracoin has fast changing difficulty

techwtf:

As long as mining generate profit, that thing wont happen at all, miners have the intensive to configure backup pools & do other preparations in order to continue mining if the pool is down / other bad things happen.

mustyoshi:

Why would somebody spend the money to develop, then deploy the miners just to pull them offline? They'd make more money by continuing to mine...

Even if they were to just do this out of hatred, the network would adapt rather quickly.

gmaxwell:

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If two of the largest miners of bitcoin went offline, the entire bitcoin economy would be at a standstill for at least several days.
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Blocks taking 2 - 3x longer than nominal is hardly "at a standstill". If there is so much hashpower consolidation that this would be a severe concern then our security model would have already failed— it's not like you need a majority hashpower to make moderate reorganizations and transaction reversals with some success.

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This is less likely with bitcoin today, but it is a real vulnerability.
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I don't think it's clear that it is. Being just a small multiple slower would be annoying, but if left us short capacity competition for space would attract larger transaction fees, which would make mining more profitable, which would draw in more hashrate.

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What can we do about that? Terracoin has fast changing difficulty
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And ended up with exploitable vulnerabilities multiple times as a result of their tinkering there.  Continuous difficulty adjustment halves the cost for an attacker to mine down a fork for use in isolation attacks.

Presumably if the network were ever stranded— and people somehow still cared about Bitcoin at all (it not clear to me how those two things could ever be true)— then it wouldn't be too difficult to do a single point hardfork to step the difficulty back down. Considering that, I think this is not worth worrying about.

🏰 TradeFortress 🏰:

A block taking 30 minutes is still acceptable. We get a hour or more without blocks frequently too. A block taking 6 hours would be a bigger problem, however it still would not represent the death of Bitcoin and it's implausible that we'd get 90% hashpower loss.

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