Uh... yes? Are you seriously trying to imply that would be legal?
If someone ever cracks modern encryption, that doesn't mean they can do whatever they want with everyone's accounts everywhere. If you find an exploit and exploit it, that's illegal.
No, but that's not the same. Signatures and checks are covered by terms & conditions (and law) that you must follow.
A better anology is if you figure out a mathematical advantage within the rules of a casino game, are you allowed to win? I believe you are, as long as it's within the rules of the game. And the casinos are smart enough to create rules against any lasting mathematical advantage.
I know how to pick locks. The locks are designed to open when pins are raised by a certain amount. Doesn't mean I have a right to anything I can unlock.
The intention of the system is to work to as security. Just because you find a way around the security doesn't mean that you are now immune to the law regarding ownership. When SHAX gets cracked, that doesn't give the person figuring it out a right to transfer all the money out of your bank account just because they figured out the math.
If private keys are proof of ownership then what's the difference between keys generated before vs keys generated after. If both keys are valid then both have then both are proof.
Private keys are not proof of ownership, they are a technical implementation detail. That crypto has been poorly designed so that keys are all people have to prove ownership is a failure of design but doesn't fundamentally change the divisibility of ownership and access. This is easily observed with a shared wallet, for example coinbase's. If an employee stole their keys, I assure you that employee would enjoy a jail yard view for the next lifetime.
If someone ever cracks modern encryption, that doesn't mean they can do whatever they want with everyone's accounts everywhere. If you find an exploit and exploit it, that's illegal.