TOTP implementation

totp.py

import hashlib
import time
import math
import hmac

def lpad(x, padlen=16):
  if len(x) >= padlen:
    return x
  return '0'*(padlen-len(x)) + x

class TOTP:

  def __init__(self, key, digest_type, digits, step):
    self.key = bytearray.fromhex(key)
    self.digest_type = digest_type
    self.digits = digits
    self.step  = step

  def create_token(self):
    cur_time = int(math.floor(time.time()))
    steps =  cur_time / self.step
    steps_hex = lpad(hex(steps)[2:])
    steps_bytes = bytearray.fromhex(steps_hex)
    hasho = hmac.new(self.key, steps_bytes, digestmod=self.digest_type).hexdigest()
    hash_bytes = bytearray.fromhex(hasho)
    offset = hash_bytes[len(hash_bytes)-1] & 0xf
    number = hash_bytes[offset:offset+4]
    token = ((number[0] & 0x7f) << 24) | ((number[1] & 0xff) << 16) | ((number[2] & 0xff) << 8) | (number[3] & 0xff)
    return token % (10**self.digits)

  
 ## Test implementation

t = TOTP('3132333435363738393031323334353637383930', hashlib.sha1, 8, 30)
print t.create_token()