[auno]

> Are your referring to AWS Multi-Factor Authentication (MFA)? It's indeed a good implementation, but it's usage is very limited and most people are not referring to this when they are talking about 2FA.

AWS is using TOTP (Time-based One-time Password) as specified by RFC 6238. Off the top of my head, the same protocol is supported by Google, Lastpass, Dropbox, Fastmail, Github, Wordpress, Evernote and Outlook.com. So it stands to argue that this is, in fact, one of the schemes most people are referring to when they are talking about 2FA.