What is this for?

If you need to generate one-time passwords using the Mobile-OTP / mOTP algorithm, from the command-line, without futzing around with your phone.

This is a self-proclaimed “standard” algorithm for one-time passwords. It is confusing, seemingly almost obsolete, and appears to mainly be used in German-speaking countries. You don't want to use this unless you are forced to interact with an existing system that uses such codes for 2FA.

Mobile apps that appear to support it:

• Swiss SafeLab OTP authenticator for iOS: on iTunes
• Swiss SafeLab OTP authenticator for Android: APK download
• Android app that supports this algorithm: DroidOTP on Google Play Store

How does it work?

The principle of the algorithm is explained badly and implemented confusingly but it's very simple: you have a token secret (an ASCII string, usually hexadecimal or alphanumeric) and a PIN (an ASCII string, usually 4 digits), and this is converted to a 6-digit code using:

counter = ASCII((UNIX epoch time) / 10s)
digest = MD5HEX(counter || secret || pin)
code = LEFT(digest, 6 characters)

That's it. ¯\_(ツ)_/¯

Use it

Requires Python 3.x.

$ ./motp.py SECRET PIN
a1b329

More verbosely:

$ ./motp.py -v SECRET PIN
Epoch time: 1549323786
Counter:    154932378

a1b329 (current)

All available options:

$ ./motp.py --help
usage: motp.py [-h] [-s SECONDS] [-l LENGTH] [-w WINDOW] [-v] secret pin

positional arguments:
  secret                mOTP secret value (often hex or alphanumeric digits)
  pin                   mOTP PIN value (usually 4 digits)

optional arguments:
  -h, --help            show this help message and exit
  -s SECONDS, --seconds SECONDS
                        Duration of mOTP codes in seconds (default 30 seconds)
  -l LENGTH, --length LENGTH
                        Length of mOTP output (default 6 characters)
  -w WINDOW, --window WINDOW
                        Number of counter values before and after current one
                        to show (for testing time-skew)
  -v, --verbose

License

MIT