Currently, some services use a second layer of veficiation if logging in from a new device:
- Gmail and Facebook send a text or call with a code
- Facebook generates a code in the mobile application
The problem is:
Countless times, I've been abroad with a cell phone whose battery had died, and needed to access my Gmail or Facebook account.
The alternative is to carry printed versions of access codes in your wallet, but this is not optimal, especially if more web services will eventually roll this out.
What other alternatives for the second layer of authentication exist that don't rely on having a mobile phone present, but would be suitable for logging on from, let's say, and old PC somewhere?
In other words, what else could Google and the others be doing?
(Please note that this question concerns two-factor authentication, and not two-step authentication as for the latter, a system could simply ask for two passwords.)