Transfer sensitive data from Ubuntu to iPhone
I’ve been extremely happy with Prompt 2 for ssh clients. It can generate keys and then I set up an isolated network interface and allow ssh in via password while both devices are isolated / secured.

You can then set up the keys as needed over ssh and then disable password if you wish on your ssh server or change back to a network where you disallow password to sign in.

On Apple to Apple you can use all sorts of other ways, too - AirDrop / iMessage / iCloud files or rely on ssh as above. Ubuntu does restrict your other methods. Also, typing out a 2048 length RSA key isn’t too horrible if you absolutely won’t compromise on user/password for temporary ssh setup to exchange keys.


https://library.panic.com/prompt/prompt-key-security/