If you tank the market and create systemic insolvency then you might hold $1B of short contracts at an exchange where the operators have packed up and fled to anonymous sandy beaches, and for all your cleverness those contracts and $10 might buy you lunch tomorrow.
> the really tricky part is breaking the private key
That's the interesting thing, you can try to brute force keys in general by just throwing enough money at the problem. Technology always advances and makes cryptography less secure.
If you tank the market and create systemic insolvency then you might hold $1B of short contracts at an exchange where the operators have packed up and fled to anonymous sandy beaches, and for all your cleverness those contracts and $10 might buy you lunch tomorrow.