time-based基于google key生成6位验证码（google authenticator）

import hmac
import base64
import struct
import hashlib
import time


def cal_google_code(secret_key):
    duration_input = int(time.time())//30
    key = base64.b32decode(secret_key)  # Length of the key must be a multiplier of eight
    msg = struct.pack(">Q", duration_input)
    google_code = hmac.new(key, msg, hashlib.sha1).digest()
    o = google_code[19] & 15
    google_code = str((struct.unpack(">I", google_code[o:o+4])[0] & 0x7fffffff) % 1000000)
    if len(google_code) == 5:  # Only if length of the code is 5, a zero will be added at the beginning of the code.
        google_code = ‘0‘ + google_code
    return google_code