"Two factor authentication is increasingly becoming a strongly
recommended way of protecting user accounts in web applications from
attackers by requiring a second method of authentication in addition
to the standard username and password pair.
Although two factor authentication can encompass a wide range of
techniques like biometrics or smart cards, the most commonly deployed
technique in web applications is the one time password. If you have
used applications like Gmail, you are probably familiar with the one
time password generated by the Google Authenticator app that's
available on iOS or Android devices.
The algorithm used for the one time password in the Google
Authenticator app is known as the Time-based One-Time Password (TOTP)
algorithm. The TOTP algorithm is a standard algorithm approved by the
IETF in (RFC 6238) totp-rfc.
It is a little known fact that you can use the TOTP algorithm to
secure your user accounts in Linux systems. This article will walk you
through the steps necessary. While the exact commands will be for
Fedora 20, the TOTP algorithm can be deployed to any Linux distro with
a little modification."
-- source: http://bit.ly/10lMmvM
Peter Reutemann, Dept. of Computer Science, University of Waikato, NZ
Ph. +64 (7) 858-5174