[Python] Index out of range on PMAC STREAM

[PokeTheCiTy]

Hi,

I may miss something on the usage of Encryptor with PMAC but I got a IndexError: list index out of range when I try to seal something big enough with it.

How to reproduce

import os
from miscreant.stream import Encryptor

nonce = os.urandom(8)
key = os.urandom(12)
encryptor = Encryptor('AES-PMAC-SIV', key, nonce)
with open('a_file', 'rb') as le_file:
    encryptor.seal(le_file.read())

I got no issue by replacing 'AES-PMAC-SIV' by 'AES-SIV'
It started to have an error with a file of 5Ko

Am I misusing PMAC algo ? Since I read it had better performance than AES-SIV, I would prefer using it as I use STREAM to encrypt large file.

Thank you

[tarcieri]

Dupe of #170.

This is a known bug in the CTZ implementation. We need to switch to using De Bruijn sequences to calculate CTZ, unless there happens to be a native CTZ for Python I'm unaware of.