It’s interesting how cryptocurrency advocacy makes otherwise intelligent people discard all principles of engineering with forceful statements like “it’s impossible,” when the only thing realistically standing between someone and as much Bitcoin as they want is SHA-2 compromise. I’m amazed with the money in play that it hasn’t happened yet. It speaks to the strength of the SHA-2 suite (and, complicatedly for me, the NSA) that it’s survived this well with a giant target on its back thanks to cryptocurrency.
Even here, you’ve assumed such an event would be a hack. Sure, one is not going to introduce trillions of coins, but a fast way to design a desired SHA-2 solution is a lot of cryptocurrencies’ factorization heel and played correctly could slowly make one incredibly wealthy (played poorly, it’d just collapse the entire currency and probably the whole idea).
You know how we’re all terrified of fast factorization and its implications for cryptography? Do you really think with the basically five minutes of research the industry has into quantum computing that SHA-2 is good enough for the entire life of a currency? We’ve already shown that coins can’t fork to change stupid shit, so I mean, good luck with an owned hash. So, hard, not impossible. Just don’t forget: once upon a time we thought MD5 was awesome and you’ve never heard of MD4.