A command-line tool for google authenticator verify code.

hotp.py

import hashlib
import hmac
import time
import struct
import base64


def compute_code(key):
    t = int(time.time())
    ts = t / 30

    ts_packed = struct.pack('>Q', ts)
    key_byte = base64.b32decode(key, casefold=True)
    hmac_result = bytearray(hmac.new(key_byte, ts_packed, hashlib.sha1).digest())

    offset = hmac_result[19] & 0xf
    bin_code = ((hmac_result[offset] & 0x7f) << 24) \
        | ((hmac_result[offset + 1] & 0xff) << 16) \
        | ((hmac_result[offset + 2] & 0xff) << 8) \
        | (hmac_result[offset + 3] & 0xff)

    bin_code = bin_code % 10**6
    return bin_code

# [guest@dd2bb0e7f6d0 ~]$ head -n 1 ~/.google_authenticator
# 3NWUJKAV3X5UK36V
key = "3NWUJKAV3X5UK36V"
print compute_code(key)

[guest@dd2bb0e7f6d0 ~]$ head -n 1 ~/.google_authenticator
3NWUJKAV3X5UK36V

$ python hotp.py
856427
$ ssh  -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null guest@localhost -p 11022
Warning: Permanently added '[localhost]:11022' (RSA) to the list of known hosts.
Verification code:
[guest@dd2bb0e7f6d0 ~]$