Oh, I recommend using a tool like Authy for sure - it uses a time-based algorithm to generate a code based on a secret whose hash is stored at a service provider (like a secondary password), so there is no service involved in generating the codes. You scan a QR code (or enter the code manually) into Authy and then you're good to go without any internet connection required to generate codes. There are open source alternatives also, but Authy is worth a try.