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by anonporridge
1669 days ago
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You really don't need to trust a "friend" while bootstrapping into the network with PoW, because the proof of work is irrevocably embedded within the blockchain, and the real world cost of creating those blocks can be pretty easily estimated. So long as you have a general idea of how much hash power is being used currently for the network, or even just how efficient ASIC computing is in general at your point in history, you can work out how great the hashing difficulty should be. You can trivially verify that the block hash with a large number of preceding zeros, e.g. 0000000000000000000b98dd8e7504793c0644cb0c27eb98f06aab9ea93c4ec2, is the hash of block it's attached to, and that a hash value that small would require a huge amount of energy to find. And every block beneath it also required a huge amount of energy, creating a huge real world economic cost to produce. You can't fake that chain without equivalent sacrifice of energy and compute resources. Anyone trying to deceive you with a false chain would have to expend approximately as much energy as the entire legitimate bitcoin network does, and then keep doing it for as long as they want to deceive you. Sure, that theoretically could happen, but the economic incentives to do it just aren't there. |
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However, that presumes all forks are soft forks; that you are presented a correct chain; that you want the soft fork with consensus rules accepted by most miners. (If verifying with an old bitcoin client the BCH BCT split will be resolved for you without you having a say.
In summary, PoW has less need for Phone a Friend than PoS. But it still has some problems.