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since with headers first it knows the amount of work on top of them and can perform the tests only probabilistically past a certain point.

Indeed, so contrary to andytoshi's assertion, pow is a form of validity. If you haven't verified every single sig yourself, can you really be called a full node?

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Great now I create a simulated history which that sets a bogus 'checkpoint' back early in the chain, but any _new_ nodes that attach to me I give this simulated history to before they know there is a better chain elsewhere and they start enforcing that rule and they are now forked off onto this bogus alternative chain;

this argument applies to any blockchain. If I can get the node to think the chain I give it is the right one before it even sees any other, I win. But here, there is still a PoW element, so as soon as the node sees a chain with higher total diff it will know the one I sent was bogus.

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Worse, because the forking off can be arbitrarily far back it becomes exponentially cheaper to do so long as hash-power is becoming exponentially cheaper.

The mechanism I proposed requires a tx that is much more recent than the block it is actually checkpointing. And there is still the normal difficulty calculation. The canonical chain as it stands and the canonical chain with a checkpoint back at block 10,000 will have heads with identical difficulty. So you can start your fork wherever you want, but so long as I haven't been partitioned off the internet completely, this isn't a problem (and if I have been, it's a problem for bitcoin proper too).

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The result is that you give miners a new power, instead of just being able to reorder the history, they could also create arbitrary inflation just by adding new utxo to their updates. (which, if course, would be in all of their short-term interests to do)

They can already do this by arbitrarily augmenting the coinbase reward. But they don't, because they know other nodes will drop the block and their efforts will go to waste. Similarly here. My proposal involved X of Y consecutive blocks to include the same checkpoint for it to be valid. Set that to 70 and 80 say. So for a checkpoint to be valid, 70 of 80 blocks in a row must include it. It is very unlikely a single entity will control all that. If they can, bitcoin is already screwed. Since they can't, they have the same incentive to be honest about the utxo set at a checkpoint as they do about following the coinbase reward schedule.

The honest proposal is the schelling point. We can easily increase the X/Y ratio to be more secure. If one pool is mining 100 blocks in a row, we have much bigger problems on our hands...

work2heat

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