I like the idea of a physical key like this a lot. I think it matters though that we are talking about something that happens 'over the air' (even if it is just

I like the idea of a physical key like this a lot. I think it matters though that we are talking about something that happens 'over the air' (even if it is just NFC). The security would need to be bulletproof. I'm not very knowledgeable how these systems work for NFC other than RFID's in credit cards. With credit cards there is a dynamic CVV code that can only be used once so if somebody sniffs your card they can't use it for more than one transaction. This might be acceptable for credit cards, but it isn't ok at all for a login scenario because if they compromise your login once, they potentially have access to all sorts of things.