You're basically asking a "you broke my workflow" kind of question. https://xkcd.com/1172/

In high school, I definitely kept password-protected private keys on a USB key that got plugged into whatever machine happened to be available. (Now I am affluent enough to carry around a real Security Key and a trusted laptop.)

If you were the maintainer, would you really want to change the defaults and deal with the backlash of complaints from users who do copy keys around?

Even the OpenSSH people will tell you not to copy private keys around. Non-ephemeral private keys should be generated where they will be used. You can copy the public key...

Okay I generated a key on a computer that I will only be using for the next 3 hours, and may never see again.

How do I install it?

Is that method actually more secure than carrying around an encrypted key?

Yep, there is no point in generating a new key if you can't get the other end to trust it. You could generate a new trusted key every time you log on (and encrypt with password), and invalidate the old key, making sure to copy it to your USB. That would roll the keys, and cause you to be locked out with that key if anyone used it. But a bit involved.

Single use login codes on paper probably the easiest way around the problem. https://www.digitalocean.com/community/tutorials/install-and...

Also, you can configure the google-authenticator TOTP module to request key and token IIRC. GA also has OTPW backup codes.

It doesn't take that long to arrive at the conclusion that you should not expose any secret to untrusted hardware.

So creating a one time use key for that computer is probably a good idea, you can revoke it once you are done using it and then it won't cause you any problems in the future.