This requires modifications to the server. I want to use normal public/private keys, without any special configuration, but instead of storing the private key i

This requires modifications to the server. I want to use normal public/private keys, without any special configuration, but instead of storing the private key in ~/.ssh/id_rsa, I want to store it in my iPhone, and authenticate via the PKCS#11 protocol. This would mean 2-factor security for all my servers and services relying on SSH, such as git, without any modifications on the server side. You would push a button on the iPhone to verify you want to authenticate, instead of typing in digits like with Google Authenticator, which is a bit of a hassle.