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A comment on Bitcoin mining hash rate drops as blackouts instituted in China. Parent comment

Re:Bitcoin mining hash rate drops as blackouts instituted in... by sillysaurusx on Sunday April 18, 2021 @01:37AM (#26850058)
Indeed. See the "bitcoin snack machine" for some hard numbers: https://bitcointalk.org/index.php?topic=423.0

> The network nodes only accept the first version of a transaction they receive to incorporate into the block they're trying to generate. When you broadcast a transaction, if someone else broadcasts a double-spend at the same time, it's a race to propagate to the most nodes first. If one has a slight head start, it'll geometrically spread through the network faster and get most of the nodes.

> A rough back-of-the-envelope example:

  1         0
  4         1
  16        4
  64        16
  80%      20%
> So if a double-spend has to wait even a second, it has a huge disadvantage.

I'm not sure anyone has put the infrastructure into place, though.

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Re:Bitcoin mining hash rate drops as blackouts instituted in... by Thorrez on Sunday April 18, 2021 @02:15AM (#26850230)
That has nothing to do with rolling back or 51% attacks. A racing attack and a 51% attack are different things.
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Re:Bitcoin mining hash rate drops as blackouts instituted in... by sillysaurusx on Sunday April 18, 2021 @02:47AM (#26850345)
Oh, you're probably right. It seemed related because the further back an adversary wanted to roll back to, the more hash power they'd need to get ahead. But it's a different category.

I wonder if there has been an analysis of how much hash power you'd need relative to how many blocks in the past you'd want to roll back.

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Re:Bitcoin mining hash rate drops as blackouts instituted in... by Thorrez on Sunday April 18, 2021 @06:25PM (#26857081)
That analysis is actually in the original 2008 bitcoin whitepaper:

https://bitcoin.org/bitcoin.pdf

If you have 51% of the power, you can roll back everything if you spend enough time on it. If you have 30%, you have a 4% chance of being able to catch up from 10 blocks behind, even if you spend infinite time on that specific fork.

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