A mathematician friend of mine pointed out that there are very few if any hash protocols that have survived for 10 years or more. What would Bitcoin’s solution be if SHA256 were to be cracked tomorrow?

SHA-256 is very strong.  It’s not like the incremental step from MD5 to SHA1.  It can last several decades unless there’s some massive breakthrough attack.

If SHA-256 became completely broken, I think we could come to some agreement about what the honest block chain was before the trouble started, lock that in and continue from there with a new hash function.

If the hash breakdown came gradually, we could transition to a new hash in an orderly way.  The software would be programmed to start using a new hash after a certain block number.  Everyone would have to upgrade by that time.  The software could save the new hash of all the old blocks to make sure a different block with the same old hash can’t be used.

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