[rkagerer]

I agree it seems sort of academic at first blush, but I'm going to venture a guess it's the idea that you own them, instead of Apple.

So you can eg. keep a backup on your own (secure) infrastructure. Transfer them when switching devices or even mirror on two different ones*. Extract your own secret enclave contents. Improve confidence they were generated securely. And depending on implementation, perhaps reduce the ease with which Apple might "accidentally" vacuum the keys up as a result of an update / order.

*Not sure how much these two make sense in the iOS ecosystem. I know on the Android side I'd absolutely love to maintain a "hot standby" phone that is an exact duplicate of my daily driver, so if I drop it in the ocean I can be up and running again in a heartbeat with zero friction (without need to restore backups, reliance on nerfed backup API's outside the ones Google uses, having to re-setup 2FA, etc. and without ever touching Google's creepy-feeling cloud).

[kbolino]

You would need to have a completely trusted software and hardware stack to actually own the keys. And that is already hard enough to get on a PC where ownership still means something, it is not going to happen on most mobile devices. To whatever extent you trust any of the stack already, the Secure Enclave is a better bet than BYOK. The real risk, as you imply, is if Apple is able to compromise the security coprocessor with an OTA firmware update, but they can definitely already push a regular OS update that exfiltrates any key you type in.

[codedokode]

Just make an airgapped Linux device on a DYI FPGA CPU. This part is not that difficult comparing to persuading commercial vendors let you use your own cloud and your own encryption/backup mechanisms.

[rkagerer]

Yeah... unfortunately it ought to be the other way around. They should have a hard time pursuading us to trust them enough to use theirs.

If your phone company asked you to give them the key to your house, in perpetuity, how would you feel about that? (Particularly if they insisted you sign a 15 page Terms of Use first that disclaims all their liability if anything goes missing).