Reference code to calculate TOTP, given a base32 secret.

calculate_totp.py

#!/usr/bin/env python3
"""
Gist to calculate Time-based One Time Password (TOTP).
This function is designed to be used in two modes:
    - Current Mode
        No timestamp supplied, and the current timestamp is considered.
        This mode gives the totp at the present moment in time.
    - Historic Mode
        Here an explicit timestamp is supplied. This is to calculate a TOTP
        that had occured at a moment in history.
"""
import hashlib
import hmac
import time
import base64
import math


def calculate_totp(secret, unix_ts=None, power=6):
    """
    The main function to calculate TOTP.
    Parameters:
        secret (str): Base32 secret for TOTP as string
        unix_ts (int): Current or arbitrary unix timestamp as integer
        power (int): Power of modulus. Essentially, the number of digits the
                     TOTP must have

    Returns:
        final_totp (int): Final calculated OTP as an integer.
                          Returns None if fails
    """
    print("[+] Checking secret...")
    if secret is None or secret == "":
        print("---> [!] Secret is None or empty")
        print("---> [!] Exiting...")
        return None
    try:
        print("[+] Trying to convert secret to bytes")
        secret_bytes = base64.b32decode(secret)
    except Exception as e:
        print("---> [!] Something unforeseen happened.")
        print("---> [!] Error: {}".format(e))
        print("---> [!] Exiting...")
        return None
    print("[+] Verified secret.")
    if unix_ts is None:
        print("[+] Mode:\tCurrent Mode")
        unix_ts = int(time.time())
    else:
        print("[+] Mode:\tHistoric Mode")
    print("[+] Using time:\t{}".format(int(unix_ts)))
    current_time = math.floor(int(unix_ts) / 30)
    print("[+] Calculating HMAC-SHA1 sum...")
    try:
        current_time_bytes = str(current_time).encode()
        hmac_sha1_sum = hmac.new(secret_bytes,
                                 msg=current_time_bytes,
                                 digestmod=hashlib.sha1)
        print("---> [+] HMAC-SHA1 sum:\t{}".format(hmac_sha1_sum.hexdigest()))
    except Exception as e:
        print("---> [!] Something unforeseen happened.")
        print("---> [!] Error: {}".format(e))
        print("---> [!] Exiting...")
        return None
    hmac_sha1_sum_int = int(hmac_sha1_sum.hexdigest(), 16)
    print("---> [+] HMAC-SHA1 sum (int):\t{}".format(hmac_sha1_sum_int))
    mod_power = 10 ** power
    print("[+] Calculating TOTP with power:\t{}".format(mod_power))
    temp_totp = hmac_sha1_sum_int % mod_power
    print("[+] Checking if padding is required")
    if temp_totp < (mod_power / 10):
        print("---> [+] Padding OTP")
        while temp_totp < (mod_power / 10):
            temp_totp = temp_totp * 10
    else:
        print("---> [+] No padding required...")
    final_otp = temp_totp
    return final_otp


if __name__ == "__main__":
    print("\n\n-------TESTS-------\n\n")
    CURRENT_TIME_TOTP = calculate_totp("RPFYC5FREUVZ22I7")
    print("[+] Current Time TOTP: {}".format(CURRENT_TIME_TOTP))

    ARBITRARY_TIME_TOTP = calculate_totp("RPFYC5FREUVZ22I7",
                                         unix_ts=829974000)
    print("[+] Arbitrary Time TOTP: {}".format(ARBITRARY_TIME_TOTP))
    # Output = 719686

    ARBITRARY_POWER_TOTP = calculate_totp("RPFYC5FREUVZ22I7",
                                          power=8)
    print("[+] Arbitrary Time TOTP: {}".format(ARBITRARY_POWER_TOTP))
    # Output = 25683649

    ARBITRARY_ALL_TOTP = calculate_totp("RPFYC5FREUVZ22I7",
                                        unix_ts=829974000,
                                        power=4)
    print("[+] Arbitrary All TOTP: {}".format(ARBITRARY_ALL_TOTP))
    # Output = 9686

Sample Output

-------TESTS-------


[+] Checking secret...
[+] Trying to convert secret to bytes
[+] Verified secret.
[+] Mode:	Current Mode
[+] Using time:	1556530685
[+] Calculating HMAC-SHA1 sum...
---> [+] HMAC-SHA1 sum:	af36e8501ed3ffd5265b1f4d9b755fb47381fdad
---> [+] HMAC-SHA1 sum (int):	1000297862448795695855358663194777220994000092589
[+] Calculating TOTP with power:	1000000
[+] Checking if padding is required
---> [+] Padding OTP
[+] Current Time TOTP: 925890
[+] Checking secret...
[+] Trying to convert secret to bytes
[+] Verified secret.
[+] Mode:	Historic Mode
[+] Using time:	829974000
[+] Calculating HMAC-SHA1 sum...
---> [+] HMAC-SHA1 sum:	e94e53eec2130b7add2d08a4ac5baf8247231cc6
---> [+] HMAC-SHA1 sum (int):	1331941619292344778698566221244933340152790719686
[+] Calculating TOTP with power:	1000000
[+] Checking if padding is required
---> [+] No padding required...
[+] Arbitrary Time TOTP: 719686
[+] Checking secret...
[+] Trying to convert secret to bytes
[+] Verified secret.
[+] Mode:	Current Mode
[+] Using time:	1556530685
[+] Calculating HMAC-SHA1 sum...
---> [+] HMAC-SHA1 sum:	af36e8501ed3ffd5265b1f4d9b755fb47381fdad
---> [+] HMAC-SHA1 sum (int):	1000297862448795695855358663194777220994000092589
[+] Calculating TOTP with power:	100000000
[+] Checking if padding is required
---> [+] Padding OTP
[+] Arbitrary Time TOTP: 92589000
[+] Checking secret...
[+] Trying to convert secret to bytes
[+] Verified secret.
[+] Mode:	Historic Mode
[+] Using time:	829974000
[+] Calculating HMAC-SHA1 sum...
---> [+] HMAC-SHA1 sum:	e94e53eec2130b7add2d08a4ac5baf8247231cc6
---> [+] HMAC-SHA1 sum (int):	1331941619292344778698566221244933340152790719686
[+] Calculating TOTP with power:	10000
[+] Checking if padding is required
---> [+] No padding required...
[+] Arbitrary All TOTP: 9686