ubytes = [ord(c) for c in os.urandom(16)] # use /dev/urandom if possible
        bytes = [bytes[i] ^ ubytes[i] for i in range(16)]
    except NotImplementedError:
        pass
    ## xor bytes with constant ctokens
    bytes = ''.join(chr(c ^ ctokens[i]) for i,c in enumerate(bytes))
    return str(uuid.UUID(bytes=bytes, version=4))