Reference used was ISO/IEC 18004, 1st Edition (2000)

This implementation is informed by my specific needs, i.e. to provide two-factor authentication for mobile phones running Google Authenticator.

• "Byte" mode only (don't need e.g. numeric mode or kanji mode).
• Encode only (no detection/decode).
• Basic supporting library functions provided (HOTP, PNG image functions) to allow full-cyle demo.

1. Download repo and compile with erl -make
2. Install Google Authenticator App on your mobile:
   • iPhone: http://itunes.apple.com/us/app/google-authenticator/id388497605?mt=8
   • Android: https://market.android.com/details?id=com.google.android.apps.authenticator
3. Run demo: qrcode_demo:run().
4. Open the generated qrcode.png file
5. Scan the qrcode into the phone.
6. Ensure server clock is correct.
7. The value of qrcode_demo:totp() should show the same passcode as the phone.
8. Handle PINs/logins for the second part of the "two factor" according to your application design.

NOTE: This documentation is rather basic as this was open-sourced by specific request!