2fa

2fa (two factor authentication) is tiny commandline tool which implements the one-time-PIN generating functionality of the google authenticator phone app.

Given the 2fa shared secret, it generates the one-time PIN (the 2nd authentication factor)
using the standard TOPT algorithm. I wrote it to make sure I understood how google's 2fa worked,
and found it useful in its own right.


Use: 

  2fa <base-32 shared secret> [# of digits in PIN] [verify]

Verification mode is used by some websites to make sure you have the right shared secret, even if
your local time is wrong. The verification code is the PIN you'd get if the time was 0.


Examples:

  2fa xgtsihi5qtwwhaob
  068701

  2fa xgtsihi5qtwwhaob 10
  0416722948

  2fa xgtsihi5qtwwhaob verify
  verification code:  501785