totp.py

import time;
import hmac;
import hashlib;
import os;
import math;
import base64;
import struct;

def get_hotp(secret, counter):
    # get and decode shared secret
    key_string = secret.upper();
    key_material =base64.b32decode(key_string.encode());
    hmac_gen = hmac.new(key_material, counter, hashlib.sha1);
    hmac_res = hmac_gen.digest(); # generate hmac-sha1 hash
    offset = hmac_res[19] & 0xf; # get offset
    bin_int = struct.unpack(">I", hmac_res[offset:offset+4])[0]; #pull bytes from specific offset
    bin_int = bin_int & 0x7fffffff;
    return int(bin_int % (math.pow(10,6))); # get numerical values to present to user

def get_totp(secret):
    counter = struct.pack(">Q", int(time.time() / 30)); # use time based counter, 30 second refresh intervals
    return get_hotp(secret, counter);


print("");
print("google authenticator totp hash generator\n(c) stephen wan 2012\n");
secret = input("Enter secret key: ");
print("");

print("TOTP Hash   -   cycle #   -   position #");
l_hash = -1;
while (1):
    totp_hash = get_totp(secret);
    if l_hash != totp_hash and l_hash != -1:
        print("");
    l_hash = totp_hash;
    print(totp_hash, "- cycle #", int(time.time() / 30), "- position #", str(int(time.time() % 30)).zfill(2), end="\r");
    time.sleep(1);