sample script about totp

generate_totp.py

# -*- coding: utf-8 -*-

"""
This Script base on https://github.com/nathforge/pyotp
and http://yamatamemo.blogspot.jp/2011/06/oath-3.html
and http://stackoverflow.com/questions/8529265/ \
        google-authenticator-implementation-in-python

サンプルで記載しているsecretはHexspeakの一種と認識
Dartでも使っていた
http://pub.dartlang.org/packages/base32

In [1]: import base64
In [2]: import binascii
In [3]: binascii.hexlify(base64.b32decode("JBSWY3DPEHPK3PXP"))
Out[3]: '48656c6c6f21deadbeef'
"""

import time
from base64 import b32decode, _b32alphabet
import random
import hashlib
import hmac
import struct

def random_base32(length=16, random=random.SystemRandom(),
                  chars=_b32alphabet.values()):
    return ''.join(
        random.choice(chars)
        for i in xrange(length)
    )


def generate_otp(secret, now=time.time(),digest=hashlib.sha1):

    base_time = int(now // 30)
    byte_base_time = '{0:016X}'.format(base_time)
    hmac_hash = hmac.new(b32decode(secret), byte_base_time.decode\
                                            ("hex_codec"), digest).digest()

    hmac_result = []
    for c in hmac_hash:
        hmac_result.append(ord(c))

    offset = hmac_result[19] & 0xf

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

    return '{0:06d}'.format(sn % 10 ** 6)

def generate_otp2(secret, now=time.time(),digest=hashlib.sha1):

    base_time = int(now // 30)
    msg = struct.pack('>Q', base_time)
    digest = hmac.new(b32decode(secret), msg, digest).digest()

    ob = ord(digest[19])
    pos = ob & 15
    sn = struct.unpack('>I', digest[pos:pos + 4])[0] & 0x7fffffff

    return '{0:06d}'.format(sn % 10 ** 6)

if __name__ == '__main__':
    secret = "JBSWY3DPEHPK3PXP"
    print generate_otp(secret)
    print generate_otp2(secret)