I believe that Google Authenticator uses TOTP. Six digit HMAC-SHA1 TOTP from a base32 encoded secret using a 30 second timestep. At least, that has been my expe

I believe that Google Authenticator uses TOTP. Six digit HMAC-SHA1 TOTP from a base32 encoded secret using a 30 second timestep. At least, that has been my experience. I wrote an OATH client and it works with Google Authenticator using those parameters. https://github.com/w8rbt/oathgen https://github.com/w8rbt/oathgen Duo supports this as well (and also other TOTP/HOTP modes). If you have access to a Duo account, look at the 'Import Hardware Tokens' feature under 'Devices'. That's not named accurately. Really it should be named, 'Import TOTP/HOTP secrets' as that's what they ask you to import and those secrets can be used in OATH compliant HW fobs or any software that does standard TOTP/HOTP. They also allow you to import Yubikeys as well if you like (of course, that's not OATH).