otp.py

# https://medium.com/@vivian.muchen/implementing-your-own-time-based-otp-generator-3b971a31330b


import hmac
import base64

counter = 0

secret = base64.b32encode(b"password")

def low_order_4_bits(val):
	return val & 0b1111

def last_31_bits(p):
    res = bytearray()
    res.append(p[0] & 0x7F)  # 7 bits
    for b in p[1:]:
        res.append(b & 0xFF)   # 8 bits
    return res

def DT(hs):
	offset = low_order_4_bits(hs[19])
	p = hs[offset:offset+4]
	return last_31_bits(p)

def hotp(k, c):
    counter_bytes = c.to_bytes(8, byteorder='big')  # 8-byte, big-edian
    hs_hmac = hmac.new(k, counter_bytes, "sha1")
    hs = hs_hmac.digest()
    s_bits = DT(hs)
    s_num = int(s_bits.hex(), 16)
    return s_num % 10 ** 6


import datetime
import time

t = 30

def totp(k, t):
	s_since_epoch = time.mktime(datetime.datetime.now().timetuple())
	time_steps = int(s_since_epoch / t)
	return hotp(k, time_steps)