One-time-password (OTP) and its time-based version (time-based OTP, or simply TOTP) are commodity solutions to provide a second factor, in addition to simple passwords, for authentication.
Here Jose Damico proposes his way to implement a simple TOTP device using only open-source tools. The core of the project is an Arduino board connected to a small LCD. From the software perspective, the SHA-1 library comes from Cryptosuite, a cryptographic library for Arduino.
More information can be found here.
[Via: Hack A Day]