I think that many people are getting checkpoints all wrong. The real point of check points is making reorgs automatically rejected instead of coordinated by miners on the fly.

That's how I see it. I was skeptical about checkpoints at first (only because of possible new surface attacks I didn't fathom), but then I thought in non political ways and asked myself why not making them frequent so that there is added reliability? Not a coincidence that devs came to the same conclusion.

So, instead of coordinating on the fly, what is essentially taking a quick decision at any random point, checkpoints reduce the on the fly decision to a window of 10 blocks. This decision is automated otherwise. It is by miners desire, since they can run other software.

It is essentially analogous to the difference between, say, manually deleting spam and tagging known spammers to be deleted automatically.

''To abandon the work or to build on top of this newly arrived block'' is what happens all the time between blocks since the beginning of bitcoin. What changes now is only that the miner will reject competing entire reorgs which are clearly rogue.

And now I wish to recall one thing csw always said against selfish mining: that it is silly because miners themselves can orphan shadow chains. How's that any different?

This means that honesty is not an assumption but is now a demand within the checkpoint window. This adds reliability.

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Another thing is the new surface attack. Allegedly a new attack would be to create a shadow chain starting at checkpoint + 1, waiting for the next checkpoint, and publishing a longer competing chain with, say, already two blocks beyond the next checkpoint.

Aske yourself how "new" this really is. It is not new at all. It was always possible to do reorgs like this in bitcoin, starting at any random point. The checkpoint+1 point continues to be random, the difference is that, before, the reorg could go arbitrarily deep. Now it is not possible since software will automatically reject a reorg changing two publicly known check points.

Someone needs to calculate it, but it is a random walk within a boundary now, probabilities are slight different.

submitted by /u/rdar1999
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source https://www.reddit.com/r/btc/comments/9ze09c/i_think_that_many_people_are_getting_checkpoints/