While I've seen 51% and Bad-actor/rational-actor type scenarios being discussed ad nauseam, and in-depth, my searches for any sort of unpacking of the following scenarios have been fruitless:
1) "Stealth" code changes, that could get slipped in via an update, to modify network operation in some unforeseen, but yet-to-conceive exploitable way.
there are atleast 100 coders checking the code and then many people in the community that double check it too. so chances of spotting stealth code are easy
2) Someone like the World Bank establishing their own, incompatible network.
thre are 500 altcoins already, who says one of them is not a world bank invention.. and more importantly who cares? bitcoin is bitcoin and does not need to be compatible with other altcoins or fiat. people that want to exchange one for another will find a way even if the blockchains do not talk to each other.
3) Computer intelligence optimizing ("cracking") the protocol
if there was a chance that 256bit encryption was at risk, then within 24 hours private/public keypairs could be updated to 1024bit. and funds would be moved across.
never underestimate how fast an update can outpace hackers/crackers exploits.. look how fast the heartbleed was figured out and the world updated its security.. how much data or value was lost... not much...
4) Isn't it perhaps most relevant how each GH is powered, and how easily that power can be removed by tactical means
if a national blackout occured bitcoin would be the least of your worries. within 12 hours all frozen food would start to thaw out and become unusable. people wont be able to get cash out of ATMS, shops would not be able to accept credit cards or bitcoins. meaning no commerce would happen. atleast bitcoin does not have to rely on american companies (visa/mastercard) so that non americans can still use bitcoin as electronic payment whilst most banks are closed due to no access to bank details.
5) Add to that security. Who holds this metric: How secure is each GH?
restored to a previous point.. ?? im not even going to comment on the stupidity of having restore points as thats the fungability argument. bitcoin will continue on as it should, as you say it would require a hell of alot of things in combination to cause the bitcoin ledger to be re-written and governments would not waste resources or risk fiat catastrophe based on bitcoin. after all there are over 100 FIAT currencies.. do you see america trying EMP explosions in russia and china to stop the BRICS development.
as for your comments on how secure is GH.. well better than KH better than MH, but not as good as TH and definetly not as good as PH.. so dont worry about the small stuff we are over 25% nearer to EH than dropping all of the way back to GH
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