Blizzard Authenticator to TOTP convertor

ba2totp.py

#!/usr/bin/env python3

# distilled from https://github.com/jleclanche/python-bna
# only remain functionality is blizzard authenticator serial + restore code => TOTP secret conversion
# so you can use 3rd party TOTP applications
# contained in a single file so it could be audited easily and you don't have to use pip
# and support "CN-" serial courtesy of https://github.com/winauth/winauth/

import hmac
from base64 import b32encode
from hashlib import sha1
from http.client import HTTPConnection
from secrets import token_bytes
from typing import Optional
import sys

# constants.py

RSA_MOD = 104890018807986556874007710914205443157030159668034197186125678960287470894290830530618284943118405110896322835449099433232093151168250152146023319326491587651685252774820340995950744075665455681760652136576493028733914892166700899109836291180881063097461175643998356321993663868233366705340758102567742483097  # noqa
RSA_KEY = 257

HOST = "mobile-service.blizzard.com"
HOST_CN = "mobile-service.battlenet.com.cn"
PATH_INIT_RESTORE = "/enrollment/initiatePaperRestore.htm"
PATH_VALIDATE_RESTORE = "/enrollment/validatePaperRestore.htm"

# utils.py

def normalize_serial(serial: str) -> str:
	return serial.upper().replace("-", "").strip()

def prettify_serial(serial: str) -> str:
	"""
	Returns the prettified version of a serial
	It should look like XX-AAAA-BBBB-CCCC-DDDD
	"""
	serial = normalize_serial(serial)
	if len(serial) != 14:
		raise ValueError("serial %r should be 14 characters long" % (serial))

	def digits(chars):
		if not chars.isdigit():
			raise ValueError("bad serial %r" % (serial))
		return "%04i" % int((chars))

	return "%s-%s-%s-%s" % (
		serial[0:2].upper(),
		digits(serial[2:6]),
		digits(serial[6:10]),
		digits(serial[10:14]),
	)

# crypto.py

def encrypt(data: bytes) -> str:
	base_num = int(data.hex(), 16)
	n = base_num ** RSA_KEY % RSA_MOD
	ret = ""
	while n > 0:
		n, m = divmod(n, 256)
		ret = chr(m) + ret
	return ret


def decrypt(response: bytes, otp: bytes) -> bytearray:
	ret = bytearray()
	for c, e in zip(response, otp):
		ret.append(c ^ e)
	return ret

def restore_code_to_bytes(code: str) -> bytes:
	ret = bytearray()
	for c in code:
		i = ord(c)
		if 58 > i > 47:
			i -= 48
		else:
			mod = i - 55
			if i > 72:
				mod -= 1
			if i > 75:
				mod -= 1
			if i > 78:
				mod -= 1
			if i > 82:
				mod -= 1
			i = mod
		ret.append(i)

	return bytes(ret)

# http.py

class HTTPError(Exception):
	def __init__(self, msg, response):
		self.response = response
		super().__init__(msg)

def get_server_response(data: Optional[str], host: str, path: str) -> bytes:
	conn = HTTPConnection(host)
	conn.request("POST", path, data)
	response = conn.getresponse()

	if response.status != 200:
		raise HTTPError("%s returned status %i" % (host, response.status), response)

	ret = response.read()
	conn.close()
	return ret

def restore(serial: str, restore_code: str) -> str:
	restore_code = restore_code.upper()
	serial = normalize_serial(serial)
	if len(restore_code) != 10:
		raise ValueError(f"invalid restore code (should be 10 characters): {restore_code}")

	if serial[0:2] == "CN":
		host = HOST_CN
	else:
		host = HOST

	challenge = initiate_paper_restore(host, serial)
	if len(challenge) != 32:
		raise ValueError("Bad challenge length (expected 32, got %i)" % (len(challenge)))

	code = restore_code_to_bytes(restore_code)
	hash = hmac.new(code, serial.encode() + challenge, digestmod=sha1).digest()

	otp = token_bytes(20)
	e = encrypt(hash + otp)
	response = validate_paper_restore(host, serial + e)
	secret = decrypt(response, otp)

	return b32encode(secret).decode()

def initiate_paper_restore(host:str, serial: str) -> bytes:
	return get_server_response(serial, host, PATH_INIT_RESTORE)


def validate_paper_restore(host:str, data: str) -> bytes:
	try:
		response = get_server_response(data, host, PATH_VALIDATE_RESTORE)
	except HTTPError as e:
		if e.response.status == 600:
			raise HTTPError("Invalid serial or restore key", e.response)
		else:
			raise
	return response

# main
if __name__ == "__main__":
	print("serial: ", file = sys.stderr, end = "")
	serial = input()
	print("restore code: ", file = sys.stderr, end = "")
	restore_code = input()

	secret = restore(serial, restore_code)
	print("secret: {}".format(secret), file = sys.stderr)

	serial = prettify_serial(serial)
	uri = "otpauth://totp/{issuer}:{serial}?secret={secret}&issuer={issuer}&digits=8".format(
		issuer = "Blizzard", serial = serial, secret = secret)
	# pipe to qrencode like `./ba2totp.py |qrencode -t utf8`
	print(uri, end = "")