I keep an ssh key on a USB drive on my keychain. The physical analogy to a key is easy to grasp and totally appropriate. You don't expect to get into your house

I keep an ssh key on a USB drive on my keychain. The physical analogy to a key is easy to grasp and totally appropriate. You don't expect to get into your house without your keys; similarly, if we turn the key into a physical object on your person, we can build off an existing habit. I don't think this should be terribly difficult.