If I'm bank of america, and i publicize a public key, and then everytime everyone does a transaction, i sign a receipt using my public key such that my customers can prove that transaction happened, then that would be the cryptography.

if bank of america does something malicious, i can prove in court very trivially through those signed receipts that they did so.

So I don't need to trust bank of america - i just need to trust the courts to charge financial institutions that provably are breaking the law.