Disclaimer: I work for a competitor. Multi-party computation (MPC) enables you to participate in public key cryptography with shares ("parts") of a private key

Disclaimer: I work for a competitor. Multi-party computation (MPC) enables you to participate in public key cryptography with shares ("parts") of a private key divided between multiple participants from the get-go, i.e. without ever having the private key in memory at any point in time. So for example, if you divide the shares between mobile devices and servers then all of them would need to communicate with one another to sign a message without any of them knowing the private key. There are variants (e.g. 2 out of N, etc.), but that's the gist of it. Connecting it to cryptocurrency wallets, you can then use this scheme to create accounts where the control is shared between multiple devices and "mathematically" it doesn't matter then if one of the devices is compromised - it could never do anything on its own.