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Why is this idea flawed? It doesn't seem to be a bad idea at first, because the miners should be incentivized to extend existing chain, instead of to "remine existing blocks", since such "remining" apparently requires more work to be done.
What's the actual reason? Because it would make double spending easier? Or it would enable miners to do selfish mining when they occasionally find a block with extra-small hash? Or it would cause more forks / require more confirmations?
I don't think this problem is duplicate with another question, because difficulty decides validity of a single block, while accumulated work decides best chain.
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Possible duplicate of Why aren't block hashes used directly as scores for difficulty purposes?
– chytrik – 2018-12-12T22:00:45.783@chytrik I think this is a different question, because difficulty decides validity of a single block, while accumulated work decides best chain. – Chris Chen – 2018-12-12T22:04:18.840
the same principles apply: accumulated work is evaluated with each new block to decide the best chain, and thus it potentially affects the validity of one block against another at the same height. This leads to the answer: every valid hash must be ‘equally valid’, or else the game theory that incentivizes miners to always mine at the chain tip will be changed. – chytrik – 2018-12-12T22:36:23.920
@chytrik AFAIK, difficulty is evaluated with each old block of previous difficulty adjustment period, then accumulated work is evaluated with difficulty of current difficulty adjustment period (which also leads to inaccuracy). – Chris Chen – 2018-12-12T22:50:39.390
That is correct. And so evaluating accumulated work (ie, which chain is the longest chain) by using the actual block hash instead of the difficulty makes some block hashes 'better than others', and thus leads to problems with double-spend attacks, selfish mining, etc. – chytrik – 2018-12-12T23:05:29.230
Oh, evaluating accumulated work with difficulty should not lead to inaccuracy. I've probably made a mistake. – Chris Chen – 2018-12-12T23:11:52.447
Yes, the block hash must be less than the value defined by the difficulty. But your conclusion does not follow, because a block hash that is significantly below the difficulty target would be 'better' than one that is only just below it, thus altering the miner's incentives. For extended discussion we could use this site's chatroom: https://chat.stackexchange.com/rooms/8089/mempool
– chytrik – 2018-12-12T23:20:15.893@chytrik The incentives of miners are indeedly altered, but, their incentive to mine at the chain tip still seems to stay unchanged. This is true even for selfish miners(when they don't have their private chains), even selfish miners won't remine against any existing block, they would just withhold their blocks privately. (Sorry, but I still don't have enough reputation to chat) – Chris Chen – 2018-12-12T23:49:28.037
Let us continue this discussion in chat.
– chytrik – 2018-12-12T23:56:41.810