As long as the machine is on, can't the attacker ask the YubiKey to generate signatures on their behalf? For the 2FA OTP portion: No. The button needs to be ph

As long as the machine is on, can't the attacker ask the YubiKey to generate signatures on their behalf? For the 2FA OTP portion: No. The button needs to be physically touched. For the PGP (ssh) portion: Yes. (but again, the attacker can not obtain a copy of the private key, that's the critical difference to your scenario) That's why (at least for critical servers) you should combine the two. That way an attacker can at most piggyback your connections. He can not initiate his own because he can not touch the button.