I think that would be the public key. You can roughly think of it as the hardware key has a private key embedded in it in a way that it (supposedly) can't be g

I think that would be the public key. You can roughly think of it as the hardware key has a private key embedded in it in a way that it (supposedly) can't be gotten off. That private key has a corresponding public key. You can think of the private key as the password and the public key as the username. So I think the public key is the "key ID" you're looking for.