In the twin example, what is to prevent your twin from taking your documentation and receiving a public/private key in your name? Or simply access that key of

In the twin example, what is to prevent your twin from taking your documentation and receiving a public/private key in your name? Or simply access that key of yours and use it? The public/private key only prove you hold the keys, not that you are you. Not identity, just proves you have access to the keys.