If that is cracked nothing is safe.
All Fiat banking, all information systems, defense systems, nukes, etc.
If you had the power to do this, you could hold the world for ransom.
If you had this power, why only go after Bitcoin, why not go after everything?
Because people would race to create alternatives and everything would be chaos. You might be better of acting like you didn't break it and know all the secrets of your enemy.
sha256 is more important for binary and document integrity than secrets. for example an adversary could alter binary packages and load them with malware and the digital signatures would check out. or just replace transactions or whole blocks in the bitcoin blockchain. that would be some trolling...
