We may never find out. The financial incentive to keep it secret is too great. If someone broke SHA-256, they could generate blocks directing all coins to thei

We may never find out. The financial incentive to keep it secret is too great. If someone broke SHA-256, they could generate blocks directing all coins to their own address and thus destroy the entire system. However, in that scenario it is likely that everybody else would roll the chain back to before the break and restart it with a different algorithm (likely SHA-3). In summary, an obvious compromise would get caught and neutralized. So a wily possessor of an SHA-256 break would use it subtly. Most likely they would target “lost” coins that haven’t moved in decades that nobody will notice are missing. Not Satoshi’s though. Too much heat.