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Author Topic: Can a majority of nodes impose shorter block intervals without harming Bitcoin?  (Read 321 times)
TinfoilHat
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November 25, 2017, 03:36:36 PM
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We know if a majority (in terms of hash power) of nodes form a coalition, they can basically reap all the rewards by refusing to add blocks mined outside of the coalition to chain. However, this also severely damages security of Bitcoin as the same coalition can also mount double-spend attacks. It is very likely that this will drop the value of currency and hence, might be unprofitable for miners.

However, I wonder what happens if the majority just decides to agree on a lower PoW difficulty and hence, shorter block intervals. There seems to be some research that suggests Bitcoin might still be secure with shorter block intervals. See the quote from https://www.coindesk.com/lower-bitcoin-block-time-scale/:

    ”According to my research the one-minute block interval seems like the most plausible. I don’t mean that it provides sufficient security, but that it would provide the same security as bitcoin has today.”

So my question is basically, is this behavior somewhat possible to observe in practice? Because if they do so, they will mine blocks more often and the blocks mined by others who follow the real difficulty will be valid too.
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DannyHamilton
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November 25, 2017, 04:04:51 PM
 #2

We know if a majority (in terms of hash power) of nodes form a coalition, they can basically reap all the rewards by refusing to add blocks mined outside of the coalition to chain. However, this also severely damages security of Bitcoin as the same coalition can also mount double-spend attacks. It is very likely that this will drop the value of currency and hence, might be unprofitable for miners.

This requires only a majority of hashpower, and not a majority of nodes.

However, I wonder what happens if the majority just decides to agree on a lower PoW difficulty and hence, shorter block intervals. There seems to be some research that suggests Bitcoin might still be secure with shorter block intervals. See the quote from https://www.coindesk.com/lower-bitcoin-block-time-scale/:

    ”According to my research the one-minute block interval seems like the most plausible. I don’t mean that it provides sufficient security, but that it would provide the same security as bitcoin has today.”

So my question is basically, is this behavior somewhat possible to observe in practice? Because if they do so, they will mine blocks more often and the blocks mined by others who follow the real difficulty will be valid too.

Every full node client (including those that are not participating in mining) would reject the blocks that are created with insufficient difficulty (regardless of the length of the chain).  The rule isn't that the "longest chain wins", the rule is that the "longest VALID chain wins."  If a majority of hashpower were to cooperate in mining these lower difficulty blocks, then it would result in a fork such that anyone that isn't running a compatible node or wallet would never see any of these lower difficulty blocks, and anyone that is running a compatible node or wallet would see only these lower difficulty blocks.

If a minority of hash hashpower were to cooperate in mining these lower difficulty blocks, then their blocks would continually be orphaned by the longer chain of normal difficulty blocks.

TierNolan
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November 25, 2017, 04:17:16 PM
 #3

So my question is basically, is this behavior somewhat possible to observe in practice? Because if they do so, they will mine blocks more often and the blocks mined by others who follow the real difficulty will be valid too.

Miners can't reduce the block interval.

To get faster blocks, miners would need to increase how much hashing power that they have.  They can't do that, since they only have so much hardware.

They could try to tweak the timestamps to fool the algorithm.  They would pretend that 2 weeks have passed, but really only 1 week has passed.  This would lead to timestamps in the future, and the users of the network would reject their blocks.

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Borilla
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November 25, 2017, 07:19:45 PM
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See the quote from https://www.coindesk.com/lower-bitcoin-block-time-scale/:

    ”According to my research the one-minute block interval seems like the most plausible. I don’t mean that it provides sufficient security, but that it would provide the same security as bitcoin has today.”


I don't get his simulations. How do the blocks propagate so fast?  it seems he took a theoretical model and he doesn't explain anything.

with 1 min blocks you would have forks everywhere
DannyHamilton
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November 25, 2017, 08:43:54 PM
 #5

So my question is basically, is this behavior somewhat possible to observe in practice? Because if they do so, they will mine blocks more often and the blocks mined by others who follow the real difficulty will be valid too.

Miners can't reduce the block interval.

To get faster blocks, miners would need to increase how much hashing power that they have.  They can't do that, since they only have so much hardware.

They could try to tweak the timestamps to fool the algorithm.  They would pretend that 2 weeks have passed, but really only 1 week has passed.  This would lead to timestamps in the future, and the users of the network would reject their blocks.

Miners could agree to a reduced difficulty, and a new difficulty adjustment algorithm that keeps the block interval faster.

Like I said, all nodes and miners that don't accept the change would just ignore those blocks since they would appear to be invalid.  This is a forking change.  If the miners using the new algorithm had enough hash power, then they could maintain their fork separate from the rest of the network.  If they had less hash power than the combined rest of the world, then their blocks would just keep getting orphaned, they would be wasting their hash power on blocks that would not even get accepted by those with the same software as them.

TierNolan
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November 26, 2017, 11:03:05 PM
 #6

Miners could agree to a reduced difficulty, and a new difficulty adjustment algorithm that keeps the block interval faster.

No they can't.  The difficulty algorithm is part of the code that the users of the system are running.

Quote
Like I said, all nodes and miners that don't accept the change would just ignore those blocks since they would appear to be invalid.

Ok, we agree then.

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DannyHamilton
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November 27, 2017, 01:06:12 PM
 #7

Miners could agree to a reduced difficulty, and a new difficulty adjustment algorithm that keeps the block interval faster.

No they can't.  The difficulty algorithm is part of the code that the users of the system are running.

Did you even read the thread.

There is nothing stopping a miner from changing the code that he is running with.  There is nothing stopping other users from using the same changed code as those miners.

In my opinion it would be a dumb thing to do, since very few people would bother using that fork, and the miner would be wasting all that hash power on something that isn't likely to gain much value...

But users chase altcoins all day every day.  P.T. Barnum would be proud.

Quote
Like I said, all nodes and miners that don't accept the change would just ignore those blocks since they would appear to be invalid.
Ok, we agree then.

That should have been clear from my posts in this thread.

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