The second is a hardwarr based approach (Yubikey) which connect to your device using USB, 'Yubikey has private key program to it's internal memory and provide one time code at login' samer way viz Google's authenticro.
The second is a hardware based approach (Yubikey) which connects to your device using USB. Yubikey has a private key programmed to its internal memory and provides a one time code at login in the same way as Google Authenticator.